ok guys-recently my 929 has been developing a low rpm stumble to it-anything less than around 2200 rpms it idles fine, but if you give it any more than 1/4 throttle it bucks and stumbles and kicks-then at 2kish-it launches. when you give it full throttle from idle in neutral you can hear it lug for a split second-its a 2001 with a full muzzy exaust, power commander III, and k&n filter. It just started doing this recently (well after the mods) and richening the mixture (or leaning it for that matter) has no effect on the problem-neither does changing maps on the power commander. It runs great after 2k-can't keep the front wheel on the ground-but the stumble is irratating and hurts my launch-anyone have any ideas? the bike has almost 14k on it. Mike

thanks, problem is irratating as h***

I have almost any spare part that could need changing-should i buy a set of spark plugs for it? no smoking or abnormal noise besides the lugging. thanks again. Mike

 

Sounds like mine did when I fouled a plug...try changing and see if it goes away. Has it been getting rained on in the last few days?

 

ALWAYS kept indoors-never left in the rain-but i have a sneaking suspicion either the fuel filters getting plugged or the plugs need changing-almost 14k seems to be warranting a new one of both if they havent been done-keep the suggestions coming, Mike

 

yeah its gotta be plugs..., or fuel injectors? cause thats how my friends f4i is, has trouble holding idle but does fine in high rpm plus he knocks when wheeli'n

 

idles fine-runs great everywhere else-just has a stumble-everyone says deal with it-but im going to keep looking. Mike

 

I just went some rounds with a 929 last week at work, and I know exactly what you're talking about. Does the exhaust eliminate the valve that the stock system has? If it eliminated the excv (exhaust control valve) you still have to run the servo motor under the tank. It has a cable that also operates the flap in the airbox. If you disconnected it, you'll get an FI code (usually 9 flashes of the FI light). It will also run like you are describing if the cables for the exhaust valve and/or the airbox flap are adjusted wrong.

 

yes-got rid of the exup-and the cables, and the airbox flapper-gutted the entire system. left the servo hooked up in the default position as well, and no fi light. also, it ran great for over 1000 miles after i did all the mods-the sputtering just started-this is why i doubt its the servo or exup. Mike

 

The only other thing I can think of is the throttle position sensor. You can check it with an analog ohm meter. Disconnect the plug and put the probes from the meter on the top and middle pins on the t.p.s. Set the meter for resistance (ohms) and slowly turn the throttle. You should be able to watch the needle on the meter move smoothly from fully closed to fully open throttle. If there are any flat or dead spots, the t.p.s. is bad. Hopefully that will help you find the problem.

 

CHANGE THE PLUGS, THEY MIGHT BE WORN FROM BAD FUEL MIXTURE. ALSO CHECK THE TIMIMG, AND POWER COMMANDER PROGRAM. IF THE BIKES TO LEAN, YOU'LL KILL PLUGS ALOT FASTER THAN NORMAL, SO YOU'LL THINK ''IT CAN'T BE THE PLUGS I JUST CHANGED THEM''. I HOPE THIS HELPS...