Czech Motorcycles

Today in Motorcycle History

Too Much Smoke

is never enough

A treatise on CZ & Jawa by Andy Reid

Sun Dec 24 2006
panzergranate at hotmail dot com
Rear Sprocket Bearing Failure.
Type 638 and Type 632 TS 350
This is an interesting fault that a friend has had on a Type 640 Blue Style, a friend in Montenegro has similar on a TS 350 Type 638 and I have on what started out as a Type 632 but has been retrofitted with a full powered 34 BHP unrestricted 1986 Type 638 KS 350 Mk.I.

OK this fault manifest itself as power loss in top gear. The owner will usually investigate the engine, carb, wheels, etc. but it turns out that it is in fact the rear sprocket bearing dragging but not quite seizing. My friend here in the UK found that his drive sprocket ran in an elliptical manner as well.

At present I'm running my bike in 3rd gear mainly at around 55 - 60 MPH tops as top gear has the bike thinking that it is climbing a steep hill into a headwind. It's like riding a Russian motorcycle!! This same engine propelled a Type 638 outfit running a Velorex 700 sidecar to 89 MPH on 18:52 final drive ratio before I changed it over to the solo, thinking I had an engine problem with the original power plant.
When crowbarred into a 1981 CZ 350 MK.III. Custom Sport it would hit 78 MPH in 3rd gear at the 7,000 redline and 105 MPH in top when tucked in behind the fairing.
I'm planning to change the sprocket drive over the Christmas Holidays and will post the post mortem of the offending drive unit on this site to help others diagnose this problem.

It is worth checking out the drive sprocket on all JAWAs and CZs experiencing loss of speed and power for no logical reason.

Andy Reid.
Poole, Dorset, UK

Strangling Killjoys

I have several pictures of the outfit and it even featured as a cover picture on one of the 2006 UK JAWA/CZ Owner's Club newsletter. It is infamous in the club for winning annual National Rally Grot Bike awards when I take it to a rally that is. So far the bike has managed around the 50,000 mile mark mainly with a Type 632 as the original Type 638 engine had been rebuilt by an idiot who didn't understand crank cases need sealant in between them. The bike had done 47 miles with no oil when I discovered this omission when the top gear selector ceased to exist!! Fortunately only the gears and my language were blue on taking the engine apart to find out the cause. The previous owner had also run the engine at 40:1 and so the centre bearings were dying from oil starvation when I bought it for £80 10 years ago.

In the owner's club over here there is much discussion and arguments about the 33:1 versus 40:1 lunacy (guess which camp I stand in!!) One person argued at the bar at one rally that as modern 2 stroke oil is better than what it was 30 years ago, one can use less of it for the same effect. Some old boy shot him down with the simple line of, quote, "Gearbox oil is better than it was 30 years ago but yer wouldn't half fill your gearbox now would you??!!"

Basically the 40:1 sticker is for government killjoy emission testers and experienced owners will ignore it and run on 33:1 instead.

I don't know if you have TS 350s or even had KS 350 versions down where you are. The KS ran from 1986 to 1988 and is recognizable by the fact that the rev counter safe rev range goes all the way around to 7,000 RPM. This is the full power 34 BHP at 6,500 engine which is totally bloody useless for pulling sidecars compared to the Type 634 before it. The engine has all 4 transfer ports active in the cylinders and has longer exhausts than the post 1988 models. A few people, including myself, have seen the speedo go all the way to the end of the range. I managed to see the needle point straight down to the PAL symbol (125 MPHish) with a KS engine crowbared into a CZ Type 471 frame running ALLSPEED Expansion chambers for a brief 2 miles before my nerves and common sense overrode my throttle hand!! I also had a tent and stuffed throwover bags on the back as well!!

The post 1988 TS 350 is restricted by baffle end collars (easily removed), pistons with narrow cut out so as to not use 2 of the 4 inlet ports and in some cases, a washer in the carb manifold. These are the 22 - 25 BHP versions and the rev counter safe range stops at 5,500 RPM, not that the restrictors ever let the engine pass this even in neutral at full throttle.

We derestrict as many strangled TS 350s as we come across for grateful owners in my neck of the woods here in the UK.

My current ride for the winter is a 1991 TS 350 fitted with a 1994 Type 640 350cc engine KS pistons and Type 640 expansion race pipes. It's also ported out and gas flowed.

I used to drag race Suzuki GT 550s in the 1980's and enjoy tuning engines whenever possible. You name it, lawnmower, cement mixer, etc. I'll have a go porting and tuning the bloody thing just for the hell of it. JAWAs tune up really nicely and aren't as fragile as the motors from the land of monkey metal. I once pulled a 9.91 quarter on a GT 550 B running on Nitro Toluene/Petrol mixture and had 3 out of 5 clutch pillars snap off doing it. Wouldn't happen on a JAWA!!

I'll send some picture over when I scan them from the albums. I have quite a few rare UK only JAWAs and CZs in photographs I've taken over the years.


Holy Rollers

The APPY 350 is my 1979 Italian licence built Aprilia CZ 350 extremely modified and tuned, ported, gas flowed, etc. way back in 1991. It now resides in various pieces on shelves around the workshop. At the time of the picture it had done 78,000 miles.

CZ Aprilia 350.jpg
CZ Aprilia 350

The Custom picture is of one of the 6 CZ 350 Custom Sport Mk.III.s, this example lives in the Brighton area on the south coast of England. I own one, and one is somewhere in Cornwall so 3 more are unaccounted for. This one has been modded with All Speed road legal pipes and a shortened saddle unit.
[No image as yet. Ed.]

The Vatican CZ 500 proves that some folks believe that maybe God is dumb enough to ride a Harley, though being the supreme all knowing being, why??!!, but his Son rides CZs currently parked at the Vatican awaiting the second coming sometime in the mid 21st century.

CZ 500 Vatican.jpg
CZ 500 Vatican

The Mustang racer is a Type 22 production circuit racer from the 1960's that was for sale at a bike autojumble this year. It is not a conversion.

CZ 350 V4.jpg
CZ 350 V4


Pneumatic drill on wheels

I was referring to the JAWA KS and later restricted TS 350s that we had here in the UK. MZ sufferers are generally regarded as mad looneys for enduring the primitive machines they ride.

A mate, Dave Cherrett, who owned a tuned CZ 125 Type 476, challenged a loud mouthed MZ 250 rider to a 3.5 mile race back from a pub at a Swindon JAWA/CZ owners club branch rally. (MZders are always invited so that us JAWA and CZ riders have something to feel superiour to!!) Anyhow the pair of them disappeared away from us dawdlers at warp speed down this country road. When we arrived back at the campsite someone there asked what was going on. Apparently Dav had charged into the site on the CZ, put it on the side stand, pulled a ciggy out of his pocket whilst lobbing his helmet into the tent, snapped the ciggy in half, lit it, and stood there casually. A half minute later the MZ 250 turned up, rode over to Dave, glared at him and then rode off. Dave had a framed speeding ticket at home for overtaking and passing an unmarked Police traffic car and being followed for 3 miles at between 98 and 104 MPH on the CZ 125. It could do 78 in 3rd gear alone!!

That was back in the 1980's and he was a learner back then, Petrol was 24% toluene tetra ethyl lead and not the 10 to 12% unleaded crap we have now over here now.

The MZder had been boasting to everone how he raced his bike in the then 1980's ACU MZ racing league and how crap JAWAs and CZs were. I think that Dave proved the point somehow.

That reminds me of the time my brother and myself went on a protest run into London against leg "protectors" (breakers!!) back in 1988 from a JAWA branch rally at Braintree. We went along with two MZders who were on a ETZ 250 and the then new ETZ 300 which was a forerunner of the ETZ 301. To read the number plate or tax disc on the ETZ 300 the engine must not be running. Any resemblance to a pneumatic drill on wheels is coincidential!!

Anyhow my brother was on his GT 380 M fitted with All Speeds formula 3 expansion pipes, K&N filters and GT 550 M needles and slides plus 40+ oversize main jets. The GT actually did 20 MPG more to the gallon returning 65 MPG then it did stock!! I was on a 1981 CZ 350 Mk.III. Sports Custom which was stock apart from a foam airfilter instead of the stock blotting paper item.

As usual for a group ride out we let the slowest bikes, the MZs lead, the 300 being in front. The ride started off down the A10 at 60 MPH but the 300 kept looking in his mirror and upping the pace. In the end, after about 10 miles we were doing 85 MPH in a fog bank. My younger brother, more used to making smog then breathing it, decided enough was enough and dialled in the warp drive and overtook them. I did the same on the CZ 350 passing them at 95 MPH plus and we both disappeared into the distance.

We didn't see them at the protest in amongst all the thousands of bikes there stopping London's traffic. (The government dropped the idea after that!!). Back at the rally site they were rather quiet and less bragging about their machines. Phil Culley, a UK club fun guy and stirrer asked what had happened to make the MZders so quiet. We told him and he said that he would try not to mention it too much at the bar but just enough to wind them up.

My old CZ 350 Sports Custom Mk.III. could push 101 MPH on the clock if I tucked in behind the fairing. I lost the top gear selector at 34,000 miles and laid the bike up as I have 14 others to ride. I bought a 1994 JAWA Type 640 Blue Style engine and expansion pipes from the local JAWA dealers. The bike was one I used to service and was now a crash wreck, hit whilst parked of all things.

I resurrected the CZ 350 with this engine which was OK but when the swinging arm seized on the left hand side and snapped off I moved the engine into a Type 632 chassis which I am riding at the moment.

On the subject of the JAWA rear sprocket bearing failures and dragging sprockets, I took apart my sprocket assembly today and found that the sprocket hub carrier bearing had shifted/been installed wrongly during dealer service (I bought the bike when it had done 4,500 miles which is out of warranty!!) and also the bearing ticks when rotated. The spacer on the sprocket hub carrier bearing no longer did its job of preventing the sprocket hub from rubbing against the chain case which resulted in the bike going like it had a hand brake locked on.

A friend, Timbo has found the same on a 1993 JAWA Type 640 Blue Style with a bearing failure resulting in the sprocket actually running in an up and down elliptical fashion, catching on the chaincase and limiting the bikes top speed to 50 MPH in 3rd and no go in top.

A friend, Aco in Montenegro, has just replaced a sprocket hub carrier bearing on his 1991 Type 638 TS 350 as it was dragging so badly that he couldn't make more than 100 KMH. and only in 3rd gear. He said that the bearing was so bad that even Russian ones look better.

This problem seem to only affect 1991 and onwards bikes and the bearings seem to be sub JAWA standard cost cutting exercise items.

OK the problem seems to be a lack of power in the engine with no go in the motor when actually it is a load increase on the motor that is sapping the power. All because of a cheap beaing!!


An Infestation of Gremlins

my son rode his pushbike into school today and so, not having to rush out to yet another simple roadside repair on his JAWA 50 that he could have done himself (Geez, how hard isit to unblock a jet on a BING carb for Chrisakes!!), I was able to work on the TS 350 Type 640 at last.

OK the rear sprocket was replaced so that now I can power down steep hills in top gear without loosing speed!! The culprit sprocket decided to run freely without the ticking I had noticed a week earlier during the recce "what parts do I need" investigation. However, what I did notice was scoring on the inside of the inner chain case cover on the rearmost 1/8th part of the orifice.

On investigation with the new sprocket, tightening up the sprocket lock nut would have the casing acting as a brake on the sprocket hub, loosening it had it move freely. I took it apart, examined everything, put it back together several time with the same result, locked nearly solid when done up properly. In the end I left the thing off as I do on the outfit to ease chain refitment as outfits eat those Jap cheapo to make but expensive to buy chains, I mention no names (DID, Izumi, etc.)

Other gremlins still infesting the bike after a 2 year layup are the base gasket sealant blown really badly but being a JAWA it still runs. Loose ignition spades on the coils. (Why JAWA don't have ring terminals ala CZ God only knows!!) and on Sunday during a moped marathon ride with my son and his friend Ragz on their JAWA Babetta/Mustang Hybrid 50 and SACH Mad Ass 50 (Unrestricted) of 24 miles to Swanage through the Purbeck Hills, the final drive bearing seal decided to let go. All I can say is, thank God it wasn't on a Jap bike as a major rebuild would be in order. On the JAWA it was a 5 minute roadside replace and repair occasion.

The camera was a freebee and pick up on any ultraviolet reflective surfaces, even in bad light. Using digital is so different from using chemical film and a bit of a learning curve.

I used to write regularly for a now defunct UK motorcycle magazine called the "Used Motorcycle Guide" usually on the dark arts of making JAWAs and CZs run extremely well and fast. I've had someone come up to me at a bike rally in the late 1990's, quote me chapter and verse about hotrodding CZ 175s and ask me if I'd read it. "Read it!!", I replied, "I wrote it!!" he rushed off an had me sign his copy. Worth far more than the money I was paid. To actually have someone understand the technicalities of what I had written and to then have a go at exploring them is why I wrote the piece.

I'm normally an electronics design engineer and so when something fails I want to know why and how it failed so I can maybe circumvent, modify or expect similar failures again in an item. JAWAs are machines made by engineers for engineers to appreciate. I own both Japanese and Czech bikes and the latter are the better built machines. Being clever with a design isn't necessarily better.

I've always had CZs and JAWAs around throughout my biking life. A friend owns 138 bikes at the moment and over 40 of those ar Czech. He keeps a JAWA Mustang in his living room, next to the TV so as to always have something interesting to look at on an evening. His wife is equally barmy!!

Back to CZs. To make a CZ Type 476 125cc do faster than the stock 61 MPH simply remove the airfilter, using a hard metal rod and a lump hammer bend/buckle the power sapping restrictor pipe out of the way of the exit hole in the plenum chamber, fit everything back together again. Hey presto, easier starting, no more overheating on long runs and a top speed of 76 MPH instantly. On the 175 the same mod pushes the top speed up to 85 MPH in one hit. The pipe is in the post 1974 models to make them slower than the CZ 250 twin which did 76 MPH as the Deluxe and 85 MPH as the Sport model. The Italian built Aprilia models did 92 MPH but ran high compression ASSO Werk pistons.

Fitting a K&N filter plus 100 mian jet to a CZ 125 Type 476 will allow it to do an indicated 84 MPH. I managed 89 MPH on the clock of my 1977 CZ 175 Type 477 on a motorway back in 1988 and it was frighteningly smooth and happy at that speed.

On the CZ 125, finally fitting an expansion pipe of suitable dimensions, usually sourced for an aircooled Yamaha RD for a simple fitment, a bit of carb fettling, an 18 tooth front sprocket to repleace the stock 16 tooth item and a good downhill starting drag will allow the rider to maybe see the speedo needle move past the 90 MPH marker.

Dave Cherrett's ton up CZ 125 was a 1978 model ruunig all SKF low friction racing bearings in the engine and wheel, exhaust port was +3mm., inlets +2mm. with the Scnurle Loop angle set to fire the mixture higher into the cylinder. The head was skimmed using grinding paste until compression was measured at 186 PSI cold as opposed to the stock 126 PSI cold.

It was built to prey on the then (1980's) common Jap sport 125s on the UK roads such as The LC 125, RG 125, AR 125 and GP 125 which it would leave easily. It could also out handle and out corner the Jap competition at the time. The bike managed 34,000 well thrashed miles in this condition until the frame lugs holding the swinging arm came off of the frame and the bike was dismantled for parts. We had a newer project in progress by this time, an 110 MPH CZ 350 fitted with LOMAX pipes, etc.

On one occasion he race an old RD 250 DX down a country lane with the rest of us following behind as rolling spectators. Dave just disappeared into the distance, leaving the RD in a cloud of Golden Film racing two stroke. I'll have to dig out the picture and scan them as the bike gradually evolved. Needless to say, as Dave was a professional car mechanic, he understood feck all about bike engines and so left tuning and such black arts to myself. He'd ask if I could make ot go even faster and I'd ask how much money he had to spend.

The MPG of the tuned CZ 125?? We actually measured it to be 27 MPG on average. Power output?? Maybe 25 to 30 BHP on a good day.

The latter Czeta Type 487/488 125/175s don't seem to be built as well as the 1970's forerunners but I did manage to have a Type 488 125 up to 78 MPH by replacing the 20mm. AMAL with a good old 24mm. JIKOV carb.

I'm after a JIKOV SBD 2917 for my son's bike as the engine isn't too happy with the 14mm. Bing cobbled onto it at the moment.

Also I'm after an old possibly running Type 476 CZ 125 for when he is 17 next month as I have all of Dave Cherrett's old 125 tuning goodies lying around which he gave me when he became an ex-patriot/Child Support Agency exile.

So what bikes do you have then??

I could tell the tale of how Dave and myself rode 428 miles across France in one day on a pair of tuned CZ 350s to a French JAWA rally, encountering hunch backed dwarf retarded gas station attendants, unisex toilets, having Dave thrown out of a shop for pissing himself on seeing that batteries are called PILES in frogland, and other weird experiences.


1994 JAWA Type 640

actually saw a Volvo today, driven by a small old guy wearing a hat peering through the steering wheel, moving along slowly in traffic with the front right tyre dead flat. I figure he was just unaware that that is why the Swedish tank he's in veers to the right all the time.

Here in Bournemouth, England, we are in a retirement zone where bad driving is the norm, though not as bad as Londoners. A lot of the retired come from London to help drop the driving standards!!

We also have a lot of SUV drivers, usually women, who believe that being in an SUV will protect them from the concequences of their bad driving. Having an SUV over here entitles one to (A) Barge out from a side turn into flowing traffic, (B) park on the pavements without receiving a ticket, (C) speed on motorways in fig and (D) be a pain in the arse to everyone else on the road in normal vehicles. To be a exceptional pain when driving an SUV mearly tow either a horse box, large trailer or caravan.

Replaced the top end of a 1994 JAWA Type 640 yesterday. God knows how it was running as the left hand piston had lost the top ring and was actually melting. The right hand pot was devoid of rings but still helping out above 3,000 RPM, below this it was just being towed along. Despite all this the bike started easily from the kickstarter, would pull 65 MPH and was quiet. Fuel consumption was about 25 MPG though!!

We have the carb cloging problems over here as well. The unleaded piss water our engines have to run on these days leaves what can only be described as fish paste in carbs and fuel taps. If one doesn't remember to run the reserve tap once in a while, it clogs up. It's worst on cars as when they're stood for a long while the fuel lines clog up completely.

You have crap fuel where you live then as well??!!

We bought a 1979 CZ 250 Sport Roadster a few years ago that had been run for 21 years and 31,000 miles on TVO (Thick Vapourising Oil). The bike still had a top speed of 85 MPH the same as on petrol. The bike was a farm work machine and as a legitimate Agricutural vehicle was allowed to run on tractor fuel. It replaced a Yamaha DT 250 trail bike that lasted just 6 months in the role before the frame broke. Obviously only a pretend off road machine then.


1986 CZ 125 Type 487

March 3rd 2007

I bought my son a 1986 CZ 125 Type 487 for his 17th birthday last week or so ago. It was gutless, needed a push to star and had no compression when cranked over hand. Top speed was 45 MPH in 3rd gear and top struggled to hold this velocity.

I'd fixed similar before many a time.

As expected, the baffle was in the wrong way round with the hole, which should be facing rearwards, at the front. Also the end piece baffle extension was also on backwards. This restored the compression and kickstarting ability.

On road tests my son said the bike only made 60 MPH eventually and the bike also had a 2 second throttle lag. Pulling the airfilter revealed that it was (A) very dirty and (B) full of cobwebs. I replaced all the paper in the filter with foam to convert it into a washable filter. IU don't believe in wasting good quality beer tokens on throw away air filters. Tis is also a common mdification oevr here in the UK.

Top speed is over 70 MPH on 16 to 52 final sprocket ratio.

A previous owner had already done the 22mm. AMAL to 26mm. JIKOV conversion upgrade. The CZ 125 only does 58 MPH with an AMAL carb fitted as stock. Fitting a 1970's JIKOV carb adds another 20 MPH and 5 BHP to the engine.

The result is that my son now spends all his spare time riding his motorcycle while his X-Box 360 gathers dust.

The main difference betwen the old CZ Type 476/477/482 engines of the 1970's and the later Type 487/488 engines is the double race bearing on the latter. The bearing replaces the single race bearing on the crank's sprocket side. God only knows why this upgrade was decided on as it is an example of Czech over engineering. The original engine was reliable enough like it was and always outlasted Japanese engines of similar capacity.

There are next to none old Japanese 125cc bikes on the road from 1986 over here where I live as they've all died out at 15,000 to 20,000 miles.

A quick tip on repairing rusted fork legs that aren't pitted. Burnish the leg with a brass burnishing wheel on a power drill and spray with several layers of Armour All Nickaseal spray giving it a couple of days to dry. The Armour All will protect the new bare steel as the original laquer and chrome did previously. It works for me and save a fortune iun having a leg re-chromed when it will benhidden by a metal shroud or rubber gater.

Well regards,


JAWA twin gearbox failures

after fixing noumerous JAWA twin engines I can inform of the following facts concerning most common JAWA twin gearbox failures on Types 623, 471, 472, 631, 632, 633, 634, 638, 639, and 640 engines.


BIke jumps out of top gear on acceleration or just won't stay in top gear at all under load. Engine is usually over 40,000 Km./34,000 miles old. All other gears work fine.


Final drive bearing is failing and is now sloppy. Possibly caused by an over tight chain or just bearing age. The sloppiness causes the lay shaft to drive under load and gear selector fork to ride against the gear rather than float in the guide grove in the cog. This causes the fork to rub against the metal, heat up and wear away until the top part ceases to exist, hence no gear locking under load. Also the camplate on the left can also become sloppy with age and exaserbate the situation.

The camplate rivet does work loose with use and age and the unit can either be repolaced or the rivet tightened.


Replace the bearing and gear selector fork. Also fix or replace the camplate. Just replacing the fork will see the problem returning withing 120 Km./100 miles or less. The burnt out fork is just a symptom not the cause.

So far I've owned and repaired dozens of CZ 250, 305 and 350 engines with the same common fult. Also 4 x Type 631 engines, 1 x Type 632, 2 x Type 638 Mk.I. and 1 x Type 634 engines all with the same problem caused in the same way. I've even bought bikes with this problem cheaply as I knew exactly what the problem was and it was a good haggling point when buying an apparently sick bike.

As with all JAWAs the repair is only costly in time as the parts are cheap. On Type 623, 631, 632, 633 and 634 engines thgis is a simple right hand case split and so the gear oil need not even be drained as the engine will be on its left throughout the proceedure. I've actually repaired one at a bike rally in the middle of a field for someone. It took under an hour from engine out of bike to engine in. This is why out of all the engines I've rebuild or worked on, JAWAs and CZs are always favourites. How many other engines can have the gearbox cluster changed with the gear oil remaining in the engine.

Anyhow I hop[e that this help a lot of folks solve a major common fault in high mileage JAWAs.

just pulled apart a Type 632 with a top gear that fails to lock properly. Sure enough the final drive bearing is fecked.

No other damage is present.

The older Type 360 and earlier engines have a different and more sturdy gear change system so don't seem to be effected in the same way.


bought a replacement CZ 125 cylinder for my son's 1988 CZ 125 roadster. I plan to port it out to the same spec as I used to port the old Type 476 and 477s out for folks back in the 1980's.

Generally this will involve lifting the exhaust port by 3mm. and the transfers by 2mm. as the engines do like to rev and are held back by the port timing making the engine rasp out way before the redline, if CZs do have a redline.

The transfers themselves are a bit rough as stock and will be ground out smooth with the Scnurle loop aimed higher into the cylinder. At stock settings the gases are pushed in below the middle of the cylinder at BDC. By grinding out the little hump inside the transfer port the gases are pushed into the top half of the cylinder at BDC, after which the bike ceases to be an economical and slow comuter 125cc bike. We had a 1978 Type 476 125cc down to 27 MPG with 78 MPH in 3rd needed to catch the boottom edge of the powerband in 4th to take the bike up to the magical Ton and beyond.

I rode that bike once and according to friends riding behind in a Ford Cortina as a pace car, hit 94 MPH though I thought that I was just cruising at 75 MPH as the engine wasn't even stressed or at its limits.

Out of all the Yamahas, Suzukis et all, the CZ was my greatest achievement in speed and power increase.

It is very important to gas flow/grind out all the rough finishes in the transfers on CZ single cylinders as they are quite rough to the touch and eye.

Well regards,

Jawa CZ logo