A forum for owners of Yamaha TTR250 trail and enduro bikes!

dern · Veteran Member

Rough running after rebuild

TTRfan · Super Guru

You've covered the obvious so it must be something else disturbed or changed in the rebuild.

Could the inlet stub rubber have parted company with the aluminium piece?

Brian

dern · Veteran Member

This is making me cross now, lol.

I've stripped the carb down and it all looks ok.

I've stripped the side stand switch and cleaned that and it's now working perfectly.

I've put a new plug in the engine and I replaced the coil and the spark went from a pretty weak affair to a strong blue one.

I've cleaned out the water trap in the air intake system and checked the air hoses and they're all good along with the breathers.

I've taken off the inlet stub and inspected that and it looks perfect.

I've triple checked the timing.

Runs run at idle, pulls well on part throttle, starts misfiring, jerking about from about half throttle up... will accelerate on full throttle but I have to hold on tight ;)

Any ideas? I've run out of stuff to check.

Thanks,

Mark

TTRfan · Super Guru

A long shot but could the Woodruff key on the flywheel have sheared allowing the timing to move randomly?

pedrosan · Senior Member

Have you cleaned the carb/jets? Could they look ok but be partly blocked inside?

dern · Veteran Member

Cleaned the carb again today... full works, totally stripped down, carb cleaner, compressed air, the works. All looked fine. Undid all electrical connections, cleaned and remade. Checked the timing again and the valve clearances, all fine. Put it all back together and it's still the same.

Swore at it quite a bit and then phoned my local dealer and booked it in. Haven't given up on a problem on a bike or car for years and years and very confused about what could be the cause.

Anyway, they'll sort it out hopefully and then I can actually use it :)

Cheers,

Mark

TTRfan · Super Guru

When you replaced the coil, did it come with its own plug cap or did you refit your old one?

I just recalled another owner with your TTR's symptoms and the fault turned out to be with the suppressor in the plug cap. Changed the plug cap and all worked great wink

Brian

dern · Veteran Member

It came with a plug cap. The difference in the spark between the old coil and the new one was night and day. Didn't fix the problem sadly but when it is resolved it'll run better for the better coil.

Cheers.

Truxx · Veteran Member

I'd wip the head back off again double check everything in the area you messed with.

It sounds more like carb problem although it's hard to tell without hearing it myself. I read somewhere that the main jet has a collar in it to reduce it from a generic size to the required size and this can be dislodged easily if you get to heavy with compressed air/pokey sticks...
Worth replacing jets anyway really since there cheap and easy...

dern · Veteran Member

That took a little while but I did tell them I wasn't in a rush... that'll learn me :)

So, they double checked everything I did and it was all fine. The second hand coil and cap was a suspect so they put a new one on and that did make a difference but only a small one. Good to have a proper new one though.

The breakthrough came when they took the carb off and compared the settings to the manual and to the can fitted and found it wasn't set up right at all. They changed the jet and set it up right and now apparently it's fine. I have absolutely no idea why it worked before I took it apart and didn't when I put it back together. Maybe the air filter was dirtier than it looked which affected the fueling or maybe there was an air leak that I fixed unwittingly when I put it all back together. Who knows.

Anyway... very happy with that and I'll pick it up tomorrow. I wouldn't have known how to do the carb stuff, never really been an expert on them... happier with FI I'm afraid.

Time (hopefully) to get muddy :)

Cheers,

Mark

-- Edited by dern on Friday 3rd of October 2014 03:24:15 PM