XR650L Stutters at high RPM

I am trying to figure out a problem with a friend's '99 XR650L. Basically, the bike starts fine and runs fine and until you really gun it hard, say around the top of second gear, it starts to stutter, almost like it's hitting a rev limiter but I know the motor can rev higher than that. Bike is totally stock. Have already replaced spark plug, cleaned air filter, checked wiring and sprayed carb cleaner through it. Appreciate any insight.

Bear in mind though, the L is not a high revver. It makes it's max torque and horsepower around 5200 rpm. It's all downhill from there. I think it redlines around 7000. If you are below those rpm's and still cutting out, I'd consider going one up on the main jet. From what you describe, it sounds like you are just reaching it's peak power output. It goes through second gear pretty quickly. Try running it out in 4th gear on the freeway, that would give you a better idea if the main circuit is cutting out too soon.

Thanks for the reply. I hear ya' about the low rev's but my buddie says this didn't used to happen so I think something's up. Maybe the main jet is just clogged up partially...is it fairly easy to access? any tricks/shortcuts to cleaning out the jets? thx.

You might check your valves. I can't tell what your feeling but my 600 made a funny noise and vibration when the valve were tight. Also I would hear things when I rode fast desert, I found my engine mounts came loose.

You could try some carb cleaner like gumout, but the best way is to pull the float bowl. Not hard to do. Just loosen the band clamps front and rear, move the rear master brake cylinder a few inches to the rear and tie it to the frame, and you should be able to swing the bottom of the carb up towards the exhaust side enough to remove the phillips head screws on the bowl. Removing the throttle cables at the carb make it easier, but not usually necessary. I do advise getting a repair manual, either Clymer or Honda. I would also want to eliminate the possibility of the problem being electrical, a bad plug, coil, wire, or cdi unit..etc. Even a bad battery can do some weird stuff. As the prior poster stated, it wouldn't be a bad idea to check valve clearance either, but they would have to be way off for the bike to do what you describe..good luck.

I have the exact same problem with my XR650R since I did the hop-up modifications. The only thing that I have not done is to swaop out the backfire screen to a less restrictive one and to change over to a uni filter which is less restrictive. Some people have told me that it could be the rev limiter which I doubt since I didn't have this problem before the hop-up kit was done. Someone also said that I might have a leak on my newly installed intake manifold. I will check that out since the hardest part of the job was getting the old bugger out and the new one in (is there an easier way that I wasn't made aware of?). As soon as I replace the above items I'll let you know if that cures it. If not let me know what you find.


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