Hello guys. I have a '99 900rr, the bike runs great at 4000 rpm's and higher, but when I'm crusing at lower rpm's, the engine doesn't feel steady, and I also hear popping out the pipe. Somebody told it might be spark plugs, but, could it be something else? Any help and info is greatly appreciated.

 

You've got uncombusted fuel in the pipe. Troubleshoot from that perspective. The fact that it goes away when you add more air (open the throttle) implies that you are having an air\fuel mixture problem, though it could be a intermittently misfiring cylinder. With carb'd bikes, there are more situations that would cause too little air than too much fuel. Check your intakes for clogs, and change your air filter. Also pull out your plugs and see what they look like. Note any discoloration (black or white) or wetness. Post pics if you can.

How does the bike react at higher RPMs below 12MPH?

 

all good advice.

In addition. Is the stutter RPM related, or throttle input related? I know you stated 4,000 rpms... but try very hard to distiguish if its throttle input related. If its about 1/8 throttle that the conditon happens, it is more than likely a carb issue, and I would lean towards the pilot jets not adjusted correctly, or the carbs are out of sync. 1/8 throttle and under the engine runs soley on the pilot jet.

If its truly rpm related, meaning no matter what the throttle input is, then it could be as easy as your plugs, or a faulty coil.

but as jonnyx said, there are so many things it could be. A lot will depend on how well the bike maintained.

 

Thanks guys, I will keep you posted.