Re: Fourstroking @ WOT... help.
Is it definitely 4-stroking at WOT when it's slowing down? The reason I ask is last year I had a similar issue but the motor wasn't 4-stroking, it was vibrating and rattling intermittently and loosing power at top speed WOT. I rebuilt the bike over the winter, this year I have a lower mount on the muffler and that problem seems to have gone away. Not sure if it is the muffler mount that fixed the problem, cause I changed a LOT of stuff in the rebuild, but it is one of the changes that is most likely to have cured this ill...
If it IS 4-stroking then you are probably running rich at WOT. Do a plug chop while running WOT and see what she looks like. (Warm bike, ride WOT, then hit the kill switch, pull the clutch in and release the throttle all at the same time. Pedal the bike home, let the motor cool and then pull and inspect the plug)
If it does turn out to be 4-stroking and running rich you need to tune your carb a bit. You need to tell us what carb you are running before we can give you proper advice. To cure a rich condition at WOT you could try a float adjustment to lower the fuel level in the bowl (will generally lean out the mix) or run a smaller jet. Again, you'll get more accurate advice if you tell us what carb your running and what the plug looks like after a plug chop at WOT.
PS If you're still running the kit plug you might try running a NGK BP6HS plug instead and see if she runs better....
Last edited by nightcruiser; 07-23-2012 at 12:33 PM.