Andy Reid

88 Jawa 350 TS discussion forum:


Andy Reid

Andy Reid 
Andy said 2004-05-16 01:08 
 
Tuning/derestricting the JAWA Type 638 Mk.II. onwards.

Firstly remove baffles, remove the restrictor collar on the last section of the baffle (it´s the one without the section gasket!!)

Secondly remove the plastic tube in the carb connection hole inside the plenum chamber of the airbox.

Thirdly if the bike is for the Dutch (Holland) market (and also some other countries) remove the plastic airflow blocker if found (the little dam) in the airbox intake under the saddle.

This will at least bring the engine nearer to the performance of the unrestricted Mk.I. Type 638 engine and let the engine rev far higher past 6,000 RPM under load.

For Porting lift the exaust port of the cylinder sleeve to flush with the exaust tunnel in the block (4 millimetres). Inlet ports are OK as is the Schnurle loop angle so leave alone. If you really must mess with the inlet ports lift them no more than 2 millimetres.

Main jet needs to be a 115 for best effect as on the Mk.I. engine.

Also check that the carb to engine block neck doesn´t sport the additional restrictor thingee found on some models which messes up the air/fuel flow at high engine speeds. Chuck it away if you find one.

Petrol oil mixture should always be 25:1 and not 40:1 as stated on the gas tank. The 40:1 is for government emissions testers and not for actual road use by riders unless one wants wrecked centre main bearings within 20,000 miles through poor lubrication!!

A sorted Type 638 JAWA should easily pull power wheelies in first and second gear. Engine note should now be more like an old Yamaha RD two stroke than the traditional JAWA 350 twin.

I´ve been tuning up JAWAs for decades no and so know about every trick and modification to make them run better.

Regards,
Andy.

 
 
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