engine problem

I have recently bought a KTM 125 motocross bike. I got this bike cheap as it starts and runs but will not rev to its full potential. I have fitted a new plug, stripped and cleaned the carb, decoked the exhaust but to no avail. The bike starts first time without any trouble and will rev up to about 1/4 throttle but any more and the whole engine bogs down and will not rev any higher. By holding the throttle wide open it puffs and splutters and tries to blow the exhaust off, I believe this to be a backfire? does anyone have any ideas of where I should be looking to solve this problem. many thanks. nigel.

snipped-for-privacy@yahoo.co.uk wrote in news: snipped-for-privacy@i40g2000cwc.googlegroups.com:

You pro'ly should be looking towards rec.motorcycles.tech, mate.

Sounds rich. Try leaning the upper end. mk

Try a new glow plug?

Maybe you need a smaller prop. :-)

Don't cha just hate it when that happens?

Ed Cregger

rec.motorcycles.dirt would be a better place to ask.

In the meantime, make sure the intake isn't plugged, airfilter is clean. This is a classic symptom of not enough air/running rich.

2-stroke or 4-stroke? (Guessing 2 since it's a 125) Make sure the reeds are closing and sealing properly as well.

Smaller prop? Check the clunk for gunk.

It sounds like the exhaust is still clogged or the timing is wrong.

Make CERTAIN that the exhaust is open.

Then, set the timing where it should be, and assure that it is advancing as it should.

If the timing is ok, verify that the carb fuel jet (if it has removable jets) is the correct one.

Make sure it is getting enough air.

It has been a long time since I owned a bike, but ....

Brian