JAWA-Tech-FAQ



The Big Table Of Silly Faults (maintained by koarl)
Some nice features of vehicles produced in times of Real Socialism *gg*
Anyway: We refuse any responsibility for resulting damages, better don't believe a word! Last update: 2006-07-06
That old crap won't start
	Fuel problems:
	- Condensation water in tank? Tank will rust from inside, and water isn't combustible :-)
	- Fuel in tank new or rather old? Better dispose of old fuel, the resulting troubles aren't worth the saved money!
	- Filter inside tank dirty, maybe rotten? You got dirt in petcock bores -> dismantle, clean it,
	- rubber plate gasket (the one with 5 holes) inside petcock damaged? Better renew it anyway.
	- External fuel filter applied? Paper type? A single drop of water will make it sealed, no gas/oil mix will pass through!
	  Better use plastic filter type.
	- Air hole in fuel tank cap blocked? This may happen when using tank bags or excessive lots chrome polish ;-)
	Carburator problems:
	- idle jet really clean?	
	- some jets exchanged/forgotten/stolen? Yes, this happened once...
	- Wrong air intake (defective rubber hose or carb flange gasket)?
	- Air filter OK?
	- float sunken (filled with fuel)? Drill a hole, empty out, solder cracks CAREFULLY.
	- float compressed by frozen water inside the float chamber during winter?
	- fuel overflowing from float chamber, float stuck? Float needle dirty? Regrind it!
	Ignition problems:
	- Are there really sparks coming from the plugs?
	  (a good spark should jump across a 10mm gap in free air - DANGEROUS testing!!)
	- Spark plug cables exchanged?
	- Are there more than 5kOhm from connector inner part to ground?
	  (measure with ignition OFF) - if yes, renew cables and connectors.
	- Battery new resp. charged?
	- Ignition lock rotten? Screw joints loose? Have fun finding which one, more fun when fixing it!
	- Ignition timing/interrupter switches checked?
  
Fuel dripping out somewhere
	Put away your cigarette! IMMEDIATELY!	
	Rubber gasket inside petcock worn??
	Asbestos plate gasket (on thread to tank) cracked? PTFE tape (as used by plumbers) helps fine.
	Hair crack in tank, frequently starting from the rear mounting ears. Damned, must weld or buy a new one.

Brakes are bad
	Double cam? Adjustment!
	Brake linings worn down to the rivet heads?
	Linings greased, caused by leaky wheel bearings?
	Brake drum filled with water?
	Drum rusty inside? Take abrasive paper...!
	Bowden cables rusty/stuck/bad condition?

Wet Ass Syndrome
	Seat cover maybe fissured and you parked your bike in rain before. That's usual.

Gearbox loud/bad shifting
	Damaged by lack of gear oil?
	Slotted link got loose?
	A good gearbox can be shifted smoothly and it will run quietly.

Engine running loudly
	Piston rings make noise caused by their vertical slackness.
	Cylinder cooling fins may be acoustically damped by rubber blocks.
	Crankshaft bearings noisy too..? That's bad, they need renewal, a lot of work...
	Clutch central nut loose?
	Primary chain worn (hits onto alloy case)?

Speedometer needle trembling
	Speedo drive cable needs oiling / replacement.

Speedo needle broken
	That's Czech engineers' intention. Furthermore: ignorance makes people brave... ;-)

Km/mile counter stopped long ago but speedo working still
	That's nice because it will raise the bike's value on reselling.

Engine losing oil
	That's quite common. Wipe off and refill.
	Otherwise dismantle completely and use trustworthy red HiTech silicone gasket.

Rear tyre oil stained
	Oil off the chain? The clutch operation rod got a seal inside the secondary drive shaft.
	When this gets leaky, gear oil will get on the chain.
	The chain spatters the gear oil onto the rear tyre.. until the next right curve.. =8-( )
	Remedy: simply exchange the O-ring between laminated paper and nylon plate!
	There is one more reason for oil loss in this area: the secondary driveshaft sealring is not
	the main problem. There is a spacer on the shaft, its face side is rough and will not be perfectly
	oil-tight against the sprocket.
	Treat the spacer face side with abrasive paper (grain 400) and use Loctite 243 thread sealant when
	reassembling.

Type 638: Clutch bucking
	Happens frequently. Read on to help yourself..
	Unmount kickstart/gearshift lever AFTER having it brought into starting position (pushed in, turned up).
	Then open clutch cover. Otherwise the kick starter spring will sproiiing somewhere.. *g*
	Unscrew the hexagon bolts pretensioning the clutch springs. Take out the packet of clutch plates.
	On the bottom there is a steel plate facing to the lower side of the clutch basket, touching a big
	O-ring. This plate has 25 "fingers" on the inner circumference which must be bent down for ca. 15
	to the lower side, say the inner side of the engine.
	Now you better check the central nut of the clutch basket. It often gets slack, the lock washer is not
	strong enough to fix it. Ugly tracks of grinding can be found on the inner surface of the clutch cover
	as the clutch basket gets loose.
	So better unscrew the hex nut, degrease threads in nut and on shaft, recycle the washer and refit the
	stuff using Loctite 243 and fairly apply torque. The inner part of the clutch must be kept in position by
	means of an "appropriate tool" *ggg*.
	You can save money by reversing the order of the friction plates because the innermost ones wear quicker
	for some reason.
	Refit all the parts, when mounting the clutch cover again re-use or better renew the asbestos gasket,
	only silicone is not enough here.
	You may replace the sealing ring on the kickstarter shaft by an O-ring, chances are it will be tight
	at least for one more week... *g*

Engine running unevenly
	a) carb problem?
	Dismantle, blast through compressed air, refit all jets to their respective places. Note the idle mix
	screw adjustment. Float sunk/filled with fuel? Simply shake and listen for testing.
	Float needle valve tight? Fuel cock/filter/reserve system dirty?
	b) electrical problem?
	Occurs only with breaker contact ignition, the cause of all suffering.
	Adjust the breaker timing (depending on type!): Put piston 3.25mm before TDC, now the contact shall open.
	Dial gauge and ohmmeter are helpful. Anyway, refer to your Owner's manual (you have one?) for exact values.
	Unexact adjustment will cause vibrations and bad starting habits.
	Attention! Misadjustment to the early side may cause engine damages!

Double cam brake adjustment procedure
	1 - Put bike on center stand, lift front wheel for easy turning.
	2 - First release self-locking M5 nut on pullrod, then...
	3 - turn M6 butterfly nut shortening the brake cable until the brake lining which is operated
	    from the first (lower) cam slightly touches te brake drum.
	4 - Release butterfly nut until wheel turns freely again.
	5 - Tighten self-locking M5 nut until the second cam makes the second lining slightly touch the drum.
	6 - Ready? Maybe. Otherwise repeat items 3, 4, 5 to improve the result :-)

	Notice that all is elastic, included the connection between the two brake cams.
	Therefore the indirectly (from pullrod) operated cam should be the first one which presses the lining towards the drum.
	If the front wheel can be blocked when braking from approx. 30 km/h, you made your day!

	ATTENTION! Brake cables from CZ origin are less recommendable.
	Again and again the nipples at the brake handle side jump off, especially after the winter pause :-{
	We like 2,5mm cables with Teflon bowdens which appear to be more exact and reliable.

Refitting fork shafts on types 634, 362, 360 etc. (springs mounted outside the shaft)
	The spring preload is a problem... without auxiliary means you will get mad doing this work.
	We recommend the proved method below, invented by Jawa driver Wolfgang Kitzmüller:
	- Take fork shaft(single, unmounted) and stretch to its maximum length.
	- Put grease on the spiral spring, shift it onto the shaft, followed by the covering plate bush. (picture)
	- Loosely put an appropriate hose clamp onto the shaft, prepare a tool for fixing it.
	- Put your maximum force onto bush and the spring under it,
	  push down while a helper must keep the shaft in uppermost position. 
	- Let your helper fix the hose clamp, thus fixing the compressed spring.
	- Now you can easily introduce the fork shaft into the triple tree clamps and fix it in position.
	- Remove hose clamp (dun't hurt yourself) - READY!
	
Mounting a VAPE ignition on your own (procedure verified on an engine with 6V alternator)	
	1    Unmount old alternator:
	1.1	Disconnect battery to avoid problems.
	1.2     Remove right side cover of engine to get access to the electrical stuff.
	1.3	Disconnect all cables leading to the alternator and breaker contacts.
	1.4	Unmount stator part of alternator, retained by 2 long M6 bolts with hexagon heads.
	1.5	Remove central retaining bolt of rotor (a jerk to the left will help).
	1.6	Cautiously pull off breaker cam, a hole with a M8 thread will become visible.
	1.7	Now the rotor can be removed from the crankshaft cone by turning a long M8 bolt into the central hole.
		When the bolt touches the end of the crankshaft the rotor will jump off (a jerk to the right may be necessary).
	1.8	IMPORTANT! Now shorten the fixation gudgeon which is fitted into the crankshaft cone. It is about 2mm too long,
		but finally it must fit into the groove of the new magnet rotor.
	1.9	Apply a little tip of NeverSeeze to the cone.
	2.    Unmount the old electrical stuff:
	2.1	Pull old cable harness out of the engine block.
	2.2	Remove the old voltage regulator, the cables are useless now.
		Insulate remaining cable ends (if not removed) or disconnect these cables from the ignition lock.
	2.3	Unmount old ignition coils. High tension cables and plugs will be reused!
	3    Mounting the new ignition system:
	3.1	First of all lead the new cable harness of the stator coil block through the intended holes of the adapter plate
		(alloy) and the adapter ring (steel).
	3.2	The angle position of the coil block is arbitrary, it will fit into 3 positions, but one of these will be best for
		cable routing - on the left down side.
	3.3	Use Loctite 243 to fix the retaining screws of the sensor mounting plate.
	3.4	Put new cable harness (including rubber seal) on the same route as the old one was before
	3.5	Use two M6 countersunk screws (Loctite!) to mount adapter plate and adapter ring together in the intended position
		(sensor S01 will be mounted later in its left-top place)
	3.6	Mount coil block using 3 M5 allen screws to the adapter plate montieren (Loctite!), don't squeeze the cables!
	3.7	Put magnetic rotor onto crankshaft cone, gudgeon must fit into groove!, fix with M6 hex bolt and washer (Loctite!)
	3.8	Mount sensor S01 into the rightmost position, each mounting screw retains one white ground cable lug.
		Take care that the cables do not touch the rotor! The distance between sensor and rotor tappet shall be 0,4mm.
	3.9	Connect sensor cable to the yellow plug coming out of the new cable harness.
	4.    Mount new voltage regulator:
	4.1	The decision whether to keep to the old 6V system or to change to 12V, must have been made now with all implications.
	4.2	The new regulator will fit into the position of the old one. It's a matter of taste if the cables are guided away
		to the top or bottom side. Two black wires provide the regulator with AC energy from the magnetic generator.
		The red wire is +, directly (without fuse) connected to the battery +. The white wire is ground.
		The metal regulator case is insulated from the inner circuit and can be connected to ground wihout insulation.
	5.    Mounting the new ignition coil module:
	5.1	Shorten old high tension cables for approx. 5mm and turn into the ignition coil outlets. 
		Don't forget the rubber seals!
	5.2	Mount new ignition coil module (which contains electronical components) where the old coils had been removed,
		the HT cables should face to the rear side. It might be necessary to make an adapter plate.
	5.3	Connect cable harness to ignition coil.
	6.   Killswitch:
		The new ignition can be switched off by means of the kill switch which can be mounted in any place you like.
		When the switch is operated, the blue wire is connected to ground and the ignition is disabled.	
		Alternatively, you can mount a relay which is activated by the voltage "15" from the ignition lock.
		If the ignition key is pulled off, the voltage is away, the relay goes back into its unenergized state,
		and the "normally-closed" contact connects the said blue wire to ground.
		Attention! The vehicle can be started without ignition key, if this relay is omitted. Better use a locking chain!
... and finally here can be found the almost hidden link to Piotr's secret document archive!