1990 XR600R throttle stumbles just above idle

can anyone help me or tell me why my 90 XR600r stumbles when I go to rev it. It idles fine, but as soon as I go to rev it, sometimes it will stall or sometimes there is just a hesitation and then it will rev. It is fine throughout the rest of the RPM range, 1/2, 3/4 and full throttle...no problems

The bike is all stock except for the muffler baffle being removed.

there's lot of info on this do a search for bog and it should bring up lots 4 you


Sounds like your twisting the throttle too fast...Sounds likeyou need a pumper carb.....:worthy:


My 90 had the same problem

Do all the usual things like a new/clean air filter/spark plug/clean good gas etc.

The fuel screw which is located on the bottom of the carb in front of the fuel bowl is externally adjustable ( Cool!).

It needs to be turned out aprox 2 turns from seated.

This helps a lot.

Also I swapped my pilot jet to a 2 sizes richer one.

These 2 improvements made the bike run much sharper in throttle response and off idle pull.

Keep in mind these carbs will always hesitate a bit when you grab a big handful of throttle from idle when idling, that's normal.

It doesn't do it when riding as bad but still slightly there.

As posted previously, only a pumper carb will solve that problem.

This problem is complicated by the high vacuum of these motors making initial throttle opening resistant and once it does it opens abruptly contributing to the quick throttle prob nonpumper carbs are inherantly poor for.

Also check your valve clearances.

Sloppy valve clearances will lead to poor throttle response and overall carburetion.

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