Well. I found something new that has me stumped, found it by accident when in neutral I can rev the 650 slowly and at a certain rpm the FRONT carb will start backfireing, you can pull the filter and see see the flash, the rear carb is fine, I have richen'ed the pilot screw on that carb all I can and have checked all hoses for blockage, It will only do it at that certain throttle, below or above it smooth's right out, I have found by doing it carefully the backfireing start's just when the slide's start to vibrate back and forth, any idea's? why it does'nt do it on the rear has me stumped, could it the plug wire instead of the jetting somehow? when the slide's start to move that's when it does it. thought above raising the needle on that carb only and see what happen's, think that would help???????

 

I experimented with this one, I feel it's the lowend demobilizer that causes this, I would love to see if it does it with a frequency thingy on it or the new magic CDI, my bets is it will disappear. This is quite normal.

 

I rrecently installed my DG snorkle.I noticed the same thing afterward with mine.I wish I had tried to make it do this before the mod.I was running it up thru the rpm very slowly from idle up.I had shimmed the needles up with washers, so I thought that was it.I took them out and it got to be a little less.I played with idle screws to get it as good as I could, but it still does it a little.It's roughly at 1/8 to almost 1/4 throttle.The weird thing was that turning the idle screws in to roughly 1 turn out seemed the best for the sputtering, but idled best at 2 1/2- 3 turns out. I also ran all weekend and it doesn't seem to do it under load.

 

god am i glad i found this site!!!! i was just out cleaning my air filter and had to move the machine and when i started it, fire out of the front carb. ran and got on here to see what it was.

 

Stakk,
Your choke cable is sticking, take them both off relube the tube and try it again.

 

I just purchased a 2002 p650 and did not notice the backfire/popping noise on the test drive (i guess since i was holding the throttle all the way down). Now that I have it home it does the same exact thing yours does. As far as I know mine does not have any after market items. Have you been able to fix yours and if so, what did you do...I have tried to mess with the carn settings but it does not seem to make it beter...any help would be appreciated. If it matters it only has 340 miles...I also checked/cleaned my chokes...the spings seem good?????

 

The intake backfiring is due to too lean condition. I don't know of any richer needle on 650. Your dealer may know. However, front and rear carbs have different size main jets, #138 on front and #142 on rear carb. You may try #140 or #142 on front and see if it helps. Or you may shim the needle a bit to make it richer. But if you just don't like the popping sound and there is no actual performance problem, why bother? Also, removing the air box cover will make it even leaner and would pop even more. Make sure there is no flammable fluid nearby when you do that with air box lid open. I know a guy who burned down his P650 doing that. Fuel+Oxygen+Spark=Explosion