Hi. New to group. Hope you can help me out. I have a 76 bultaco Sherpa 350. Bike starts after a few kicks. Runs ok but when you stop the bike it doesn’t want to start again. Any ideas why. Had new piston and carb looked at. Cheers. David.

How long have you had the bike? Have you ever replaced the crankshaft seals? That is where I`d start. It sounds as if when it gets hot the crank seals are leaking and letting some air in. You don`t have to split the engine to do this just pull the ignition, the clutch and primary drive off and pull the seal holders off. Replace the seals and away you go. Graham.

Do you still get spark at the plug when engine hot? Is there a fuel filter, is it clean and clear? Tank vent is this functioning? Carb looked at, how deep. Float height needs checking. The fuel in the bike how old is it, could just be stale fuel? Are the carb breather tubes kink free and clear of dirt? Is carb needle set to standard think it’s middle notch, could be wrong? Possibly crank seals as suggested by ‘bullylover’ but that ought to affect running after cold start, with as suggested lean mixture. Have you checked that new piston is ok, hasn’t nipped up has it? Air filter element is this clean, not clogged up. Ignition, check timing is correct for a 350 (325) I set the timing at 3.25 mm btdc with the contacts about to open. That’s a Mr Miller tip, makes the engine pull like a tractor but it’s more docile! Ignition coil could be breaking down when it gets hot ( broken primary or secondary winding). Condenser could also be duff, if the contact breakers are royal to dark blue on their faces this indicates the condenser. 

There, quite a bit to go at but set the contacts to man. spec. Set the carb to man. spec. Let us know how you get on.