Special thanks to Robert Fornwalt (yankeebob at dejazzd.com) for his contribution of this reproduction of the Yankee shop manual.
SECTION 1 Installation of New Bearings
1. Clean and inspect the main engine case. Carefully inspect all bearing mounting surfaces for signs of damage due to improper installation or removal of bearings. If the mounting surface appears very shiny, the bearing may have spun in the engine case. If so, Loctite Bearing Mount should be used when new bearings are installed. Also inspect the transmission backing plate dowel pin holes for signs of damage or elongation.
2. Press new bearings into the inner main bearing sleeves as well as the left side Jackshaft bearing sleeve. Note, the left main bearing sleeve is slightly larger in diameter than the right sleeve. The left Jackshaft bearing is a #6205 while both inner main bearings are No. 6205-C3. The C3 denotes greater clearance between the balls and races than in the standard 6205. The C3 bearings must be used for the inner crankshaft mains as there is greater load and therefore more heat generated at these points. When pressing these bearings into the sleeves, be certain to press only on the outer race of the bearing. Any amount of side load on the inner race of the bearing will mar the surfaces of the balls and races and the bearing will almost certainly fail.
3. Using Special Tool No. 1120-345, install the inner crankshaft seals in the main bearing sleeves. They should be pressed in just far enough so that the edge of the seal is flush with the edge of the sleeve.
4. Heat the main engine case to 250 - 300F. This takes about 25 min. in an oven set at 475F. Holding the main bearing sleeves with special tool No. 1120-321 (Fig._____) install them in the engine case. As you insert the sleeve into the case, align (as closely as possible) an oil hole in the bearing sleeve with the oil passageway in the transfer port. Using the same special tool, install the left side jackshaft bearing and sleeve. These sleeves must be fully seated in their mounting bosses. If the engine case is hot enough, the sleeves will slide easily into place. It is very important that you do not force the bearing sleeves into the engine case. Any excessive force will permanently damage the sealing surface between the bearing sleeve and the case.
5. While the engine case is still hot, install the two right side transmission bearings and the right side jackshaft bearing using special tool No. 1120-521 (Fig._____). All three of these bearings are No. 6304.
6. Again while the case is still hot, check all of the bearings and bearing sleeves you have installed to see that they remain fully seated in their mounting bosses. If any bearings have moved out slightly, you should be able to re-seat them by pushing them back into place with the blunt end of a hammer handle. If any bearings are not fully seated but will not move with gentle pushing, it will be necessary to re-heat the case.
7. Clean and inspect the right and left outer crankcase halves as well as the transmission backing plate. Again check for signs of a spun bearing and damaged or elongated dowel pin holes. Also inspect the gasket surfaces of the outer crankcase halves.
8. Heat the case halves and transmission backing plate to 250-300F. This takes about 10 minutes for the crankcase halves and 8 minutes for the backing plate in an oven set at 475F.
9. When the cases have reached the desired temperature, install the bearings as shown in Fig._____. They should simply drop into place. Make certain the bearings are fully seated in their mounting bosses. The outer main bearings in the crankcase halves are No. 6205, while the two bearings in the transmission backing plate are No. 6304.
10. The outer crankshaft seals will be installed after the final shimming of the crankshaft is completed.
SECTION 2
INSTALLATION AND SHIMMING OF CRANKSHAFTS
1. Clean and inspect the crankshaft coupler bolt and remove any old Loctite from the threads. If the Allen hex sockets of the bolt appear to be damaged in any way, the bolt should be replaced.
2. Install a new O-ring on the coupler bolt.
3. Install new woodruff keys in their slots on the inner crank halves. Slide one of the crankshafts into place through its main bearings in the engine case, making certain you do not damage the seal with the woodruff key. The cranks are marked R (or D) and L (or I) for right and left. Be certain you install them properly.
4. Slide the crankshaft into the coupler sprocket inside the case, making certain the woodruff key fits into its keyway in the sprocket. Also, make certain the primary drive chain is in place around the sprocket.
5. Start threading the coupler bolt into the inner crank half of the remaining crankshaft. Remember, one end of the bolt has right-hand threads and the other end has left-hand threads. Screw the coupler bolt in one complete turn.
6. Insert Special Tool No. 1120-341 through this crankshaft and into its hex in the coupler bolt.
7. Install the second crankshaft in the engine case. Slide it in until the coupler bolt comes in contact with the first crankshaft, and slowly turn the bolt (clockwise from the left side of the engine, counterclockwise from the right side) until you feel the bolt threading into the first crank. Ideally, the bolt should start threading into both cranks simultaneously. You can, however, be up to one complete turn off as long as you dont exceed this limit.
8. Once the threads have started properly in both crankshafts, continue to turn the coupler bolt and thereby draw the crankshafts together. The important point to remember here is that one of the woodruff keys is in its keyway (the first crank installed) but the other key (second crank) is not necessarily in its keyway. As you draw the crankshafts together, try to line up the key with its keyway. By turning one crank slightly back and forth as the two come together, you will be able to feel when the second key is in its keyway. When you are certain both keys are in their keyways, draw both cranks together as far as they will go.
9. Using Yankee Special Tool No. 1120-121, mag holding tool, hold the crankshafts from turning (Fig.____). Tighten the coupler bolt to 65 ft. lbs. Of torque.
10. Reinstall any shims that were present on the ends of the crankshaft when the engine was disassembled, and install both outer crankcase halves, using new gaskets between the mating surfaces. Use only four screws to hold each case half in place, however tighten the screws firmly to compress the gaskets. With a sharp knife, trim away any excess gasket material that protrudes from between the cases both on top of and inside the case gasket areas.
11. Using a plastic or fiber mallet, lightly tap the crankshaft all the way to the left. You can measure the end float of the crankshaft by measuring the gap between the inner race of the right outer main bearing and the right side of the crankshaft with a feeler gage (Fig.____). This can also be measured with a vernier caliper or a dial indicator on the end of the crankshaft. Measure the total amount of side to side movement of the crankshaft.
12. The proper crankshaft end float is .006 in. to .012 in. If your measurement does not fall within these tolerances, add or subtract shims accordingly to achieve the proper end float. If you must add or subtract shims, try to keep them equally distributed on both ends of the crankshaft to make the job of centering the cranks easier.
13. Once proper end float has been established, it is necessary to check the centering of the crankshaft. It may be necessary to remove shims from one end of the crankshaft and place them on the other end to insure that the connecting rods run midway between the flywheels. The procedure for checking this is as follows.
14. Obtain two old Yankee pistons of the same oversize as the cylinders and cut the tops from them (Fig.____). Install these pistons on the connecting rods using your wrist pins and wrist pin bearings. It is not necessary to install the circlips.
15. Slide the cylinders in place over the centering pistons, and look down at the connecting rods through the tops of the pistons. With a plastic or fiber mallet, lightly tap the crankshaft all the way to the left. Rotate the crankshaft 3 or 4 revolutions, and observe where the connecting rods run in relation to the sides of the crankshaft flywheels. Then, tap the crankshaft all the way to the right and repeat the test.
16. Ideally, the connecting rods should run in the center of the crankshafts, equidistant from the right-side and left-side flywheels. If the rods seem to run too close to the right side flywheels of each crank, remove shims from the right end of the crankshaft and place them on the left end of the crankshaft to move the crankshaft to the right. If the rods are too close to the left-side flywheels, move shims from the left end of the crankshaft to the right end. Do not add or subtract any shims, simply move them from one end of the crankshaft to the other end until the connecting rods run in the center of the flywheel halves.
17. If the crankshaft is centered properly but the connecting rods run too close to the outer flywheel (right rod too close to right outer flywheel, left rod too close to left outer flywheel) this can be remedied by installing Yankee Part No. 1101-457, crankshaft coupler sprocket (oversize). This oversize sprocket is designed to spread the crankshafts apart about .012 in. more than the standard coupler sprocket. If this oversize sprocket is used, it will be necessary to re-shim the crankshaft for proper end float and centering.
18. Once proper end float and centering has been established, remove the cylinders and centering pistons. Remove the outer crankcase halves, and place any shims that may have stuck to the bearing over the appropriate end of the crankshaft.
19. Using Yankee Special Tool No. 1120-345, crankshaft seal installing tool, install new seals in the outer case halves. They should be pressed in far enough so that the edge of the seal is flush with the surface of the case.
20. Apply a small quantity of high temperature grease to the sealing lips of the crank seals and install the outer crankcase halves, making certain the gaskets are in place.
21. Apply a small amount of Loctite Nut Lock (blue) to the case screws and install the screws, tightening them with an impact screwdriver. Do not use any type of Loctite other than nut lock, or the threads in the engine case could be permanently damaged. When all of the screws are tight, stake the outer edge of each screw to the engine case using a hammer and center punch (Fig._____).
SECTION 3
INSTALLATION OF TOP END COMPONENTS
1. The top end components must meet the criteria described in Chapter 2, Section 4, before they can be installed.
2. Make certain the center case gasket edges are flush with the base gasket surfaces of the case. Squirt a small amount of oil into the main bearing oil holes drilled into the transfer port cutouts.
3. Wrap clean shop rags around the connecting rods to prevent any parts or foreign material from falling into the crankcases. Slide new base gaskets over the studs and trim away any excess gasket material, which may partially block the transfer ports.
4. The piston, wrist pin, wrist pin bearing and connecting rod (small end) are all color coded to allow for a perfect fit upon assembly. The piston and wrist pin are coded either black or white. You must use a white pin with a white piston, and a black pin with a black piston as the diameters of the pin and its hole in the piston are slightly different. The wrist pin bearings are available in four sizes. Choose the proper bearing depending upon the color of the con rod and wrist pin. The chart, Fig.___, shows which bearing you will need.
NOTE: If you are in doubt as to which wrist pin bearing you possess, put the bearing inside the connecting rod and insert the wrist pin into it. The pin should be easy to slide through the bearing. Once you have the pin in place, hold the rod firmly with your fingers and try to wiggle the wrist pin inside the bearings. If any play in detectable between the pin and bearing, or if any force is required to push the pin into it, you have the wrong bearing and it should not be used.
5. Squirt a few drops of oil into the wrist pin bearing you have selected and insert it into the connecting rod.
6. Clean the wristpin in a solvent, and push it part way into the piston. Work it back and forth until it can be pushed in and out freely with your fingers. Again clean the wrist pin, and push it part way into the piston. Set the piston on top of the connecting rod with the arrow on top of the piston pointing forward. Be certain you use the right piston on the right side and the left piston on the left side if the pistons are so marked.
7. Align the piston and connecting rod properly by sliding the Yankee wrist pin drift (No. 1120-211) into the piston and through the wrist pin bearing until it butts up against the end of the wrist pin.
8. Support the piston with one hand to prevent side loading the connecting rod and push the wrist pin inward with the other until the wrist pin drift drops out (Fig.____).
NOTE: Do not attempt to position the wrist pin by hammering it with a mallet, as this may bend the
connecting rod. If the wrist pin proves difficult to move, use a wrist pin driving tool as shown in
Fig. ____to install the pin.
9. Using a pair of needle nose or duck bill pliers, install both wrist pin clips in the piston. If you can rotate either of these clips in both directions in their grooves after installation, remove and discard them and install new ones.
10. Install both rings on the piston, making sure that the small peg in each ring groove is centered between the ends of the ring. Be certain that neither ring can bind in its groove. Squirt a few drops of oil on the rings and work it around to lubricate all of each ring.
11. Repeating this procedure, install the second piston and rings on the remaining connecting rod.
12. Remove the shop rags and turn the engine very carefully until one of the pistons is at bottom dead center (B.D.C.). Slide the cylinder down over the studs until the bottom of the liner rests squarely on the top ring.
13. The bottom inside of the cylinder liner has a small chamfer machined around its circumference to make the rings easier to start into the cylinder. Using your fingers, or a ring compressor, compress the rings, being careful not to allow either ring to ride up over the peg in its groove. Carefully work the cylinder down over the piston and seat the cylinder against the engine cases. Applying a small amount of oil to the chamfer will make installation much easier.
14. Install the second cylinder in the same manner. Once both cylinders are in place, rotate the crankshaft a few times and remove any dust or dirt that may have collected at the top of the cylinders.
15. Inspect the mating surfaces of the cylinder heads and the top of the cylinders. Make certain these two surfaces are smooth and clean.
16. Place a new head gasket on each cylinder and center it on the top of the liner.
17. Slide the heads down the studs into place on the cylinders. The higher ends of the cooling fins are on the front of the heads. Fit the flat washers to the cylinder studs and mount the eight 12mm nuts, turning them down finger tight.
18. Fit a 12mm socket to a low reading torque wrench and torque the nuts to 5 ft. lbs. (60 inch lbs.) using the sequence shown in Fig.____. Repeating this sequence a second time, torque the nuts to 10 ft. lbs. (120 inch lbs.). Repeat a third and final time, using 15 ft. lbs. (180 inch lbs.).
NOTE: If you attempt to tighten the cylinder heads in any other sequence, without a torque wrench, or
with a torque wrench that is not accurate at very low readings, you run the risk of warping a
cylinder head or causing piston seizure due to cylinder distortion.
19. Once the top ends are in place, the engine should be pressure checked for air leaks. The sparkplugs and compression releases should be installed in the heads, and the exhaust and intake ports blocked off. The magneto flywheel bolts must be installed in the ends of the crankshafts. The most important areas to check for leaks are the base gaskets, inner and outer crank seals, and the inner main bearing sleeves where they mate to the engine case. If any leaks are discovered, they must be corrected before assembly continues.
SECTION 4
INSTALLATION AND TIMING OF MAGNETOS
1. The Yankee 500 Z is fitted with two separate Motoplat solid-state electronic ignition systems, one for each cylinder. These two systems are identical in operation. The only difference between them is that the right side flywheel turns in a clockwise direction, while the left side flywheel turns in a counterclockwise direction. There is an arrow on the outer perimeter of each magneto flywheel, which indicates direction of rotation. There is a reference number stamped on the face of the flywheel. This number is also stamped on the stator. Each flywheel/stator unit is a matched set, so this reference number must be the same on both flywheel and stator. You cannot use the flywheel from one Motoplat unit with the stator from another unit.
2. Examine each Woodruff key that locates the magneto flywheel on the crankshaft. If it shows any signs of wear or damage, replace it with a new one. Before fitting it into its slot in the crankshaft, lay it upside down on a hard surface and tap its rounded edge with a ball peen hammer, as shown in Fig. ____. This will very slightly widen the key so it will fit tightly in the slot and be less likely to dislodge while you are installing the magneto flywheel. Tap the keys into their slots in the crankshaft.
3. Closely examine each magneto stator for broken or cut wires or other apparent damage. Without using any harsh solvents, clean the stators thoroughly and blow them dry with compressed air. Be especially careful to remove any trace of metal filings that may be on the stators.
4. Slide the stator wires through the holes in the crankcase halves, and install the rubber grommets.
5. When you disassembled the engine you were instructed to scribe a reference line across the edge of the magneto stator and one of its mounting bosses on the engine case. Locate these marks and position the stator on the engine so that they are aligned. Install the three backing plate mounting screws and tighten them. Be certain you have the right stator on the right side and the left stator on the left side.
6. Select the right side magneto flywheel and position it in front of the crankshaft. Look through the hole in the center of the flywheel and turn it until the slot in the center is aligned with the Woodruff key on the crankshaft. Mount the flywheel on the crankshaft, pressing it into position with your hands. Tap on the face of the flywheel with the side of your hand to be sure that it has seated fully on the crankshaft. Do not install the nut.
7. When timing the Yankee engine, each cylinder is timed individually. Complete the timing procedure on one cylinder before starting on the other.
8. You will now need a dial indicator to locate the position of the piston while timing the engine. There are several types of dial indicators and sparkplug hole adapters available through most motorcycle accessory distributors or machinist supply firms. Since most of them are similar, the procedures for using them are usually the same.
9. Most timing dial gauge kits consist of a dial gauge calibrated either in millimeters or thousandths, an adapter that screws into the sparkplug hole, and a plunger that fits into the adapter, between the piston and the indicator (Fig.___). To install the gauge remove the sparkplug and screw the adapter tightly into the hole. Drop the plunger down through the center of the adapter and then set the dial indicator into the center of the adapter.
10. Slowly turn the flywheel while lightly holding the dial indicator. Continue to turn the flywheel until the piston comes up to the top of its stroke (T.D.C.). With the piston at Top Dead Center, gently push the dial indicator downward until the small needle registers 4mm. Tighten the locking screw on the adapter, which will lock the indicator in place.
11. Move the flywheel back and forth slightly until you are certain you have T.D.C. Then, rotate the face of the indicator so that the large needle reads zero (Fig.___).
12. Now turn the flywheel opposite the direction of the rotation of the engine (turn it clockwise if you are timing the left cylinder and counterclockwise if you are timing the right cylinder) until the needle completes 2.75 revolutions (2.75mm). Note, since you started at 4mm, and you are moving the indicator backwards, the gauge will now read 1.25mm.
13. Insert the timing pin, Yankee Special Tool No. 1120-111, through the small hole in the flywheel. If the magneto is timed properly, the pin will pass directly through the hole in the flywheel and into its corresponding hole in the stator.
14. If the pin does not pass into the hole in the stator it will be necessary to remove the flywheel and rotate the stator slightly in the appr9opriate direction until the pin will pass through the flywheel and into the stator at 2.75mm BTDC.
15. Once the proper timing has been attained, tighten the three stator mounting screws securely, slide the flywheel back onto the crankshaft, and again check the timing. Remove the dial indicator, plunger, and adapter.
16. Fit a new star lock washer to the crankshaft and a new O-ring on the end of they flywheel mounting bolt. Apply a few drops of Loctite to the threads of the bolt, and turn it in finger tight. Fit the Yankee flywheel holding tool (No. 1120-121) to the slots in the flywheel. Using a 26mm socket, torque the magneto flywheel nut to 60 ft. lbs. (Fig.____).
17. Sometimes the Woodruff key that locates the magneto flywheel on the crankshaft is slightly narrower that the keyway on the flywheel into which it fits. Because of this, it could be possible for the flywheel to shift slightly when the nut is torqued. For this reason, many mechanics prefer to make a precautionary timing check after the nut is torqued. Although the amount that the timing could change is very small, this final check is worth doing.
18. Repeat the timing procedure with the second cylinder, again timing is at 2.75mm BTDC.
PART B CARBURETION
OPERATION OF SINGLE NEEDLE IRZ CARBURETION
Section 1
0 to 1/8 Throttle: The Pilot Metering System (Fig.____).
1. The pilot metering system feeds fuel and air from 0 to 1/8 throttle. The fuel is metered by the pilot fuel jet. Air is metered by the low speed air screw and the carburetor slide.
2. When the throttle is closed and the engine is idling, the upward movement of the piston creates a vacuum in the intake port. This vacuum causes air to be sucked into the left-hand hole beneath the intake mouth of the carburetor. This air flows through a passage that leads to the low speed air screw. This screw meters the amount of air available to flow past a small orifice that connects to the pilot fuel jet.
3. At this orifice, the fuel and air are mixed together and then flow into the carburetor bore through a small hole just in front of the slide. The mixture then enters the engine.
4. As the throttle is opened just slightly, the fuel mixture can also enter the engine through another small hole just inside the front edge of the slide. Due to the slide being raised slightly, larger amounts of air flow over these two holes, causing more fuel to be drawn up out of them.
5. You can vary the proportion of the mixture from 0 to 1/8 throttle by changing the pilot fuel jet. A larger number jet will make the mixture richer: a small number jet will make it leaner.
6. You can also vary the mixture from 0 to 1/8 throttle by adjusting the low speed air screw. Turning this screw clockwise makes the mixture richer: turning it counter-clockwise makes it leaner.
7. The pilot metering system continues to work in conjunction with other metering systems at larger throttle openings, although its influence is greatly decreased.
Section 2
1. You will notice that the carburetor slide has its bottom edge cut away on the air intake side. This is called the slide cutaway.
2. There is a tube protruding from the bottom of the carburetor bore. This tube is called the needle jet. The tapered needle in the slide projects down into this tube, and as the slide is raised, the needle is drawn up out of the tube, metering the flow of fuel accordingly.
3. As the slide moves from 1/8 to throttle, air flows past the needle jet. If the air could flow squarely across the top of the needle jet, it would create considerable vacuum in it, therefore sucking too much fuel from it. This is the reason for the slide cutaway, so as to direct air downward against the mouth of the needle jet. This decreases the amount of vacuum formed, thereby decreasing the amount of fuel flow.
4. The higher the cutaway (stamped in millimeters on the bottom of the slide) the smaller the fuel flow (leaner mixture). The lower the cutaway, the greater the fuel flow (richer mixture).
5. The mixture at 1/8 to throttle can be varied in two ways. A needle jet with a larger hole could be fitted. However, the selection of these needle jets is limited. It is always best to vary the mixture at 1/8 to throttle by installing a slide with a higher or lower cutaway.
Section 3
to Throttle: Needle Position and Booster System (Fig.____)
1. From to throttle, the slide regulates the flow of air. As the slide is raised further above the top of the needle jet, the cutaway becomes decreasingly effective in directing the air downward. Because of this, the air flows more squarely across the top of the needle jet. This increases the amount of vacuum formed in the needle jet, thereby drawing a greater amount of fuel from it.
2. At this throttle opening, the flow of fuel is regulated by the tapered needle. As the slide moves from to throttle, the needle is withdrawn proportionately from the needle jet, thereby allowing for a greater flow of fuel.
3. The mixture at to throttle can be adjusted by raising or lowering the needle. The needle is suspended in the slide by means of a clip fitted to one of three grooves in the needle. Putting the clip in a lower notch raises the needle, making the mixture richer. Moving the clip to a higher groove lowers the needle, making the mixture leaner.
4. Because the venturi of the carburetor is round, a small upward movement of the slide at or near throttle position will allow for a much larger volume of air to flow through the carburetor bore than the same movement at a higher or lower throttle opening. This creates a greatly increased demand for fuel. The needle jet cannot supply this fuel alone, because only the volume of air flowing over it has increased, not the vacuum created in it. To compensate for this, a booster system is provided.
5. To boost the flow of fuel, air enters the center small hole beneath the intake mouth of the carburetor. (Fig.___) This air is routed directly to the needle jet through several small holes drilled halfway up it. This passage of air up the needle jet boosts the flow of fuel which is necessary to meet the demand. Although the booster system is working at all throttle openings above idle, it is most effective around throttle. There are no provisions for adjustment of the booster system on the 24 mm and 27 mm IRZ carburetors.
6. The proportion of the mixture at to throttle also affects the mixture at greater throttle openings.
Section 4
to Full Throttle: Slide and Main Jet (Fig.____)
1. From to full throttle, the additional flow of air is regulated by the position of the slide. As the slide nears the top of the bore, the cutaway has little or no effect. A higher vacuum is then created at the needle jet, drawing out an increasing amount of fuel.
2. As the needle is raised higher in the needle jet by the upward movement of the slide, it becomes less effective in metering the flow of fuel accurately. From to full throttle, the main jet controls the flow of fuel.
3. To vary the mixture from to full throttle, fit a main jet with a higher number to make it richer, or with a lower number to make it leaner.
4. NOTE: Each metering system blends gradually with the one preceding it and the one following it. The objective of regulating the carburetor is to arrive at a condition wherein there is a smooth transition from one metering system to the next and the proportion of fuel and air remains the same from closed to full throttle.
Section 5
The Float Metering Device (Fig. ___)
1. The float mechanism provides a constant level of fuel for the fuel metering system. This constant fuel pressure allows for an even rate of flow through the jets.
2. When the fuel flows through the float metering jet in the top of the float bowl, the fuel level in the bowl rises. This causes the float to rise and push the float needle up into the float metering jet. When the fuel reaches a predetermined point, the float will have risen to a point that is sufficient to fully seat the float needle in the metering jet, stopping the flow of fuel.
3. The float level is not adjustable on the 24mm 27mm IRZ carburetors.
PART B
SYNCHRONIZATION
1. When tuning the Yankee 500 Z carburetors, it is imperative that the two carburetors be in complete synchronization. Make certain that the jet size, needle size and position, and slide cutaway are identical in both carburetors.
2. Any time a carburetor slide or cable is replaced, the carbs must be re-synchronized.
3. To adjust the idle speed, start the engine, and let it warm up to operating temperature. Make the following adjustments with the engine running. If the engine is equipped with a manifold balance tube, the tube should be temporarily blocked off (not disconnected) before adjusting the carburetors.
4. The Idle RPM Screws, Fig._____, which are the spring-loaded screws on the left side of each carburetor, should both be screwed in the same amount. If one screw seems noticeably shorter or longer than the other one, back out the short one and screw in the long one until they are both adjusted the same.
5. Now adjust the idle screws to attain the desired idle speed. Turn each screw only a quarter-turn at a time, and alternate from one screw to the other. Turn the screws clockwise to increase idle RPM, counter clock-wise to decrease RPM.
6. Adjust the idle mixture screws (low speed air screws). On the right side carburetor, turn the idle mixture screw in either direction until the engine RPM begins to fall off. Using that as a starting point, turn the screw in the opposite direction, counting the number of turns until engine RPM again begins to fall off. Now turn the screw in the original direction one-half the number of turns you just counted.
7. Repeat paragraph 6 above with the idle mixture screw of the left side carburetor. Both screws should end up between and 1-1/2 turns out from the fully seated position.
8. Readjust the idle RPM Screws as in paragraph 5 to again achieve the desired idle speed.
9. Shut off the engine, and disconnect the rubber air cleaner hose assembly from the carburetors. Open the throttle as far as it will go, and stick you fingers into the bores of both carburetors. Both slides should have pulled up past the top edge of the carburetor bores. If either one is sticking down past the top of the bore and cannot be raised past it with the cable adjuster, the cable should be replaced.
10. With both slides fully up, slowly release the throttle until the slides just begin to lower past the top edge of the bores. Both slides should reach this point at the same time. If they do not, reset the cable adjusters so that both slides lower simultaneously.
11. Now release the throttle and see that both slides seat fully. There should be approximately 1/16 inch free play in both cables. If there is not, both cable adjusters should be reset to obtain the necessary free play, and then re-synchronized as in paragraph 10.
12. Replace the air cleaner boot and clamps, and readjust the idle speed screws if necessary.
PART C ELECTRICS
THE IGNITION SYSTEM
Section 1: Operation of the Ignition System
1. The Yankee 500 Z is fitted with two separate Motoplat solid-state electronic ignition systems, one for each cylinder. These two systems are identical in operation. The only difference between them is that the right side flywheel turns in a clockwise direction, while the left side flywheel turns in a counterclockwise direction. There is an arrow on the outer perimeter of each magneto flywheel which indicates direction of rotation. There is a reference number stamped on the face of the flywheel. This number is also stamped on the stator. Each flywheel/stator unit is a matched set, so this reference number must be the same on both flywheel and stator. You cannot use the flywheel from one Motoplat unit with the stator from another unit.
2. Each Motoplat ignition system consists of four basic parts:
a. A rotating magnet called a magneto flywheel.
b. A set of stationary coils, wires and diodes encased in epoxy resin. This is called a magneto stator.
c. A device similar to an ignition coil called an electrical converter.
d. A sparkplug
3. The magneto flywheel contains permanent magnets. When these magnets pass the low voltage coils on the magneto stator an AC current is formed in the coils.
4. The AC current formed in the low voltage coils then goes through a diode, which is a small electrical component that, among other things, allows current to pass through it in only one direction. Therefore, the current on the other side of the diode is DC current.
5. This DC current flows to the electrical converter or high voltage coil on the frame and charges a capacitor housed within the coil.
6. The capacitor is connected to a silicon controlled rectifier or thyristor. This thyristor will not allow the current to discharge from the capacitor until it is triggered by a separate voltage.
7. When it is time for the sparkplug to fire, a special magnet in the flywheel passes by a pickup coil on the stator. This generates a small current in the coil and it flows to the thyristor and triggers it, allowing the capacitor to discharge its current through the primary windings of the high voltage coil. As a result, a high voltage is formed in its secondary windings and the sparkplug fires.
8. To regulate the time at which the sparkplug fires, you simply rotate the magneto stator in one direction or the other on its mounting bosses. This changes the time at which the special magnet passes the pickup coil on the stator. See Part A, Chapter 3, Section _____, for details on regulating the engine timing.
9. On the Yankee Z, the magneto stator is also wired to provide charging current for the lighting system.
PART C CHAPTER 1
SECTION 2
TESTING THE IGNITION SYSTEM
1. If the engine wont run at all, runs on only one cylinder, is difficult to start, or runs very poorly and you suspect the ignition system is at fault, remove both sparkplugs from the engine. With the ignition switch turned off, operate the kickstarter a few times to remove any gasoline from the cylinders. This is to eliminate any chance of fire when testing for spark. If there is any gasoline present on the cylinder heads, let it evaporate before continuing. Fit each plug into its sparkplug cap and ground the base of each plug against the cylinder head (as far away from the sparkplug hole as possible). Turn the ignition switch on and operate the kickstarter. Watch and listen for a healthy spark at both sparkplugs. If you get a weak spark or no spark at all in one (or both) sparkplug (s), substitute new plugs and perform the test again. If you still get no spark or weak spark, the following items should be checked.
2. Remove the sparkplug cap (or caps), check for moisture corrosion, and be sure it has good contact with the stranded metal portion of the plug wire. Check for spark again.
3. If you still get no spark, remove the gas tank and check the high voltage coil mounting brackets for proper grounding. Also, check the blue and black coil leads from each magneto for moisture and corrosion. Reinstall the coil leads on their proper terminals, making sure they are a tight fit. Again check for spark.
4. If you still do not get a good spark at both plugs, remove the blue wires from terminals #8 and #11 of the ignition switch. These blue wires are the kill wires for the high voltage coils. When these wires are grounded, the coils will not fire. Be certain these wires are not touching any metal surfaces or each other, and again test for spark. Note, these wires are connected to separate terminals on the ignition switch, which are grounded when the switch is turned off. These wires must never be connected together to a single terminal kill switch, as ignition timing will be adversely affected. This is especially true if your cylinders are not firing simultaneously. (See Chapter 2, Section 2, paragraph #_____.)
5. If you now do get a proper spark at each sparkplug, the ignition switch is faulty and should be replaced.
6. If you still do not get proper spark to both plugs, remove the magneto covers from both sides of the engine, and closely inspect the wires that run from the magneto stators to the high voltage coils. Using a test light or an ohmmeter, test the wires for continuity from the terminals on the coil to the base of the wires at the stator. You must eliminate the possibility of a break (open circuit) or short in these wires. Test for spark.
7. At this point, you should be getting a good spark from at least one of the sparkplugs. You have eliminated every item that could malfunction except for the mags and coils themselves. It is highly unlikely that both mags or both coils are faulty at the same time.
8. Assuming one cylinder now has proper spark, we can determine whether it is the coil or the mag of the other cylinder that is faulty simply by switching the magneto leads (black and blue wires) from one coil to the other. Remove the mag leads from the coil that was producing spark and attach them to the coil that was not producing spark. Also, attach the mag leads from the non-sparking coil to the coil that was producing spark. Now test for spark as before.
9. If the coil that was producing proper spark still does so, both magnetos are working properly, and the non-sparking coil is bad. If the spark is now occurring at the opposite sparkplug (the one that wasnt working before) then the magneto for that side is bad.
10. Further checking of the ignition components requires the use of specialized equipment such as an oscilloscope. For this reason, if you still cannot determine which component is faulty, the best practical method for repair is to first substitute a new coil for the one on the motorcycle and test for spark. If the spark is then sufficient, you will of course, know that the old coil is defective. If you still get a weak spark, or no spark, reinstall the old coil and substitute a new magneto.
11. STROBE TIMING. If the motorcycle runs, but it lacks power and gives erratic sparkplug readings, it is possible that the magneto is producing sufficient spark, but is doing so at the wrong time, even though the magneto has been timed properly with the timing pin and dial indicator. This can easily be checked stroboscopically with an automobile type timing light.
12. First, set the timing on each cylinder as described in Part A, Chapter 3, Section 4. When you are finished, before removing the timing pin, make a line across the top of the flywheel with a piece of chalk or other suitable marking device and put a corresponding mark across from it on the engine case, as shown in Fig.___. Remove the timing pin.
13. Connect the timing light to the right side plug wire, and if it is the type that needs an external source of power, provide that source (battery, wall outlet, etc.) according to its need.
14. Start the engine and let it idle. Aim the timing light at the right side flywheel, as shown in Fig.___, and watch the marks. The mark on the flywheel will be slightly to the right of the mark on the case. Accelerate the engine to approximately 6000 R.P.M. At the point the timing will have fully advanced and the mark on the flywheel and the mark on the case should appear to be aligned.
15. If the marks did not align, turn off the engine and adjust the timing by removing the flywheel and rotating the stator. If the mark on the flywheel was to the right of the mark on the case, turn the stator counterclockwise an equivalent amount. If the mark on the flywheel was to the left of the mark on the case, turn the stator clockwise an equivalent amount. Reinstall the flywheel and check the timing again with the light.
16. If the mark on the flywheel was erratic and seemed to fire almost anywhere, or jump around quite a bit, replace the magneto.
17. Repeat steps 13 through 16 of this Section, using the left sparkplug wire and left magneto flywheel. The only difference you should see is that the timing mark on the left flywheel will be to the left of the stationary mark at idle and should advance toward the right as R.P.M. increase. Again the marks should be aligned at approximately 6000 R.P.M.
PART C ELECTRICS
THE CHARGING SYSTEM
Section 1: Operation
1. The YANKEE 500 Z is equipped with a battery operated lighting system. Alternating current is generated in two separate magneto/flywheel assemblies by permanent magnets in the flywheels passing over the lighting coils in the stators. Unlike the ignition circuits, which work independently, each charging circuit works in conjunction with the other to produce the total charging current.
2. The alternating current produced by the two magnetos is rectified and regulated by diodes in the regulator. The direct current produced at the regulator flows along a white colored wire to terminal No. 3 of the main switch. The current then flows from terminal No. 2 of the switch (when the switch is on) through a 15-amp fuse and into the battery.
3. The amount of current allowed to pass through the regulator and into the battery is dependent upon the amount of charge in the battery and the amount of drain or discharge on the system. This is accomplished through a feedback circuit from the battery to the regulator. The minimum battery voltage necessary to operate the regulator is 3.3 volts. If the battery voltage is less than this figure, no charging current will be produced by the regulator. When battery voltage reaches the maximum rated value of the regulator, 7.5 volts, and there is no drain on the system (lights turned off) the charging current will be reduced to zero.
Section 2: Checking the Charging Circuit
1. The first step in trouble shooting any electrical malfunction is to check all connections to make certain they are tight. Check all wires for shorts, and see that the correct wires are connected to one another. Also, see that the fuse (15 amp) is in good condition.
2. If the battery does not seem to be charging properly, remove it and charge it for several hours on a 6 volt battery charger rated at one amp or less. If the battery holds the charge, reinstall it and if it does not, replace it.
3. If the battery, wiring and fuse are all OK, disconnect one of the red wires from the double terminal (marked R- R) of the voltage regulator. Connect the positive lead of a DC ammeter to this wire and connect the negative lead of the ammeter to the now empty terminal of the regulator. The meter must be capable of registering at least 15 amps.
4. Connect the positive lead of a DC voltmeter (set on 10 volt scale) to the positive battery terminal, and ground the negative lead of the meter. The meter must show at least 3.3 volts. If not you must recharge the battery.
5. Turn the main switch to on, start the motorcycle, and accelerate the engine to approximately 3000 R.P.M.
6. Switch on the lights. If the voltage of the battery reads less than 7.5 volts (but more than 3.3 volts) the ammeter should read approximately 11 amps.
7. Switch off the lights and maintain 3000 R.P.M. The battery voltage should slowly increase to the rated maximum value of the regulator; 7.5 volts while the charging current should slowly decrease to zero amps. If the charging current does not decrease to zero but the battery is fully charged, replace the regulator and repeat the test.
8. If in paragraph 6 above, the battery is not fully charged but 11 amps cannot be attained, either the regulator or one of the magnetos is faulty.
9. To determine whether it is the regulator or one of the mags which is at fault, disconnect the DC ammeter and voltmeter from the motorcycle. Disconnect the Red, Yellow, and White wires at the regulator. These wires are in the same harness, and connect both magnetos to the voltage regulator.
10. Start the motorcycle and accelerate the engine to 3000 R.P.M. Using an AC voltmeter on a 0 to 50 volt scale, measure the voltage between the Red wire and White wire. Next, measure the voltage between the Red wire and Yellow wire. In both cases, the meter should read approximately 25 to 30 volts at 3000 R.P.M. If these voltages are obtained, then the regulator is faulty and should be replaced.
11. If the proper voltages were not obtained in the previous paragraph, it is necessary to check the output of each magneto individually. To do this, remove the gas tank and disconnect the Red, White, and Yellow wires from each magneto where they plug into the mag to regulator harness.
12. Again using the AC voltmeter, measure the voltage from Red to White and from Red to Yellow of one of the mags. Repeat this test with the other magneto. It is necessary to replace the gas tank, or use an auxiliary fuel supply to perform this test. At 3000 R.P.M., you should obtain 13 to 15 volts AC in all four of these checks. If any one of these checks (Red to White or Red to Yellow on each mag) failed to produce 13 to 15 volts, then that magneto is faulty.
13. If both magnetos put out the required amount of voltage individually but you could not obtain the required voltage in paragraph 10 (both mags together) then the magnetos are running out of phase, or they are wired together incorrectly.
14. If the cylinders on your engine fire simultaneously that is 0 or 360 (the stock arrangement), then the wires from both magnetos should be connected as follows: Red to Red; White to White; Yellow to Yellow. See Fig. No.______.
15. If the cylinders on your engine fire 180 apart (the Yankee engine can be assembled to fire that way) then the magneto wires should be connected as follows: Red to Red; White to Yellow; Yellow to White. See Fig. No._____.
16. If your cylinders fire at neither 0 nor 180 apart, then one of two things have happened. Either someone has rebuilt the engine using a non-standard crankshaft coupler sprocket (available in 15, 30, 45, 75, 90, 105, and 150 on limited basis) or, a woodruff key has sheared inside the crankshaft coupler sprocket, allowing one of the crankshafts to twist out of alignment with the other. If the latter is the case, it will be necessary to disassemble the engine, separate the crankshafts and replace the woodruff key to realign the crankshafts.
17. If you have a non-standard coupler sprocket, the magneto lighting wires should be connected as follows to produce charging current.
Distance from T.D.C. of Right |
Lighting Wires from Each Mag | ||
Cylinder to T.D.C. of Left Cylinder |
Connected Together | ||
0 |
Red to Red-White to White-Yellow to Yellow | ||
15 |
R to R W to W Y to Y | ||
*30 |
R to R W to W Y to Y | ||
45 |
R to R W to Y Y to W | ||
75 |
R to R W to Y Y to W | ||
*90 |
R to R W to W Y to Y | ||
105 |
R to R W to W Y to Y | ||
*150 |
R to R W to W Y to Y | ||
180 |
R to R W to Y Y to W | ||
| NOTE: 30, 90, and 150 will work equally well wired either W to W, Y to Y, or W to Y, Y to W. Red must always connect to Red. |
