On Thu, 30 Mar 2006 15:21:18 GMT, mike wrote:

Gary Brady wrote in news:BQHWf.9275
:

wrote:
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.

Sounds like it might be a plugged exhaust system. I see you've
"decoked
the exhaust", but have you looked for dirt dauber nests in the
expansion
chamber or muffler, etc.?


From whats described it could be any of; carb jet blockage, wrong slide
setting, slide needle position, choke blockage, airfilter clogged,
exhaust blockage, and depending on the year the exhaust powervalve might
be seized closed or the operating cable broken or disconnected.

The one thing I've not seen suggested yet is to check the magneto.
I've had the same symptoms from a bad magneto. It would run fine till
I tried to push it and then it would start missing till I eased off. I
tried everything and finally took it to a dealer who found the bad
magneto.