So I've got myself another project bike.

'93 JTR160 with a 250 motor in it as the previous owner couldn't find a 160 piston.

it starts 2nd kick no problems, runs off choke happily. After 5-10 mins or so it's revs begin to pick as if the dry side main seal is passing air.

let it cool down and it's back to normal.

ill do a vacuum test on it this week, but could it be a stator problem?

any suggestions?

graeme

I meant '94 not '93.

 took it as a '94from the frame number?

"1694" (160cc 1994)?

do you know the year from the frame number?

regardless of that, any ideas on the running issues?

Thanks for the clarification. It rides really nicely. Just got sort out this problem, then I can concentrate on tidying it up a bit.

Have you cleaned the carb and jets? It could be dirt blocking the pilot jet then settling back down into the float bowl when the engine is stopped.

I'll pull it out and get it through the ultrasonic cleaner too. I just need to go through the bike completely. It will make a nice bike I reckon.

Ok, I've put a new main seal in on the dry side.

carb has been cleaned in the ultrasonic bath.

can anyone tell me what size the pilot jet should be?

the motor is behaving the same way. Revs begin to rise steadily then level off. A bit of choke settles it down, so it's still running lean.

hmmmmm?

Sounds like it needs some new rim decals or maybe anodised bar ends.

All the best,

Scott 

 

It sounds like the engine is getting a lean mixture.  Check to see if the fuel tank is venting correctly.  A simple test is when it starts to rev up is to loosen the fuel cap.  If it slows down, the vent is plugged.

Well Ive managed to sort it all out.

the gasket between the reed block and intake manifold was letting air in. Took me ages to find because I took the reed block off to seal the motor for a vacuum test.

the gasket in question was a piece of gasket paper, cut out to fit. Replaced it and happy days.

i like this old bike. It rides really nicely.

I have just got hold of a similar bike, doesn't look as clean as yours though, in need of new plastics for it which seem impossible to find!