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k_laud

uncorked 650 jetting woes...help!

14 posts in this topic

I am trying to mess with the jetting and what-not on my dad's XR so I can use it tomorrow for my motorcycle license test. It's being a pain in the butt, so I figured I'd ask you all if you had any insight into the situation. Especially you guys with the BRP (big red pig).

First of all, I uncorked it for him, so it has the HRC exhaust tip and the bigger intake manifold, and put in a 68s pilot and a 175 main. I also pulled out the snorkel and the plastic baffle in the airbox It runs fine at high rpm, but when backing off, it was backfiring. Sometimes when letting off and coming to a stop, it dies. I have been playing with the fuel screw (on the right side of the carb) and the idle screw, cause I figure it's only doing weird things at low throttle positions. Then, to cure the backfiring, I lowered the float level so gas wouldn't pour back into the airbox. We started it up, and it hasn't wanted to backfire, but it won't idle cleanly. If you rev it up, it won't idle down for about 5 or 10 seconds. What's up with that? It seems like I fixed one thing, and messed up another. I just don't get what could make the thing not idle down for that amount of time.

Any help you can give today would be appreciated cause I gotta ride the damn thing tomorrow to get my license! I am used to working on 2-strokes, so I'm only learning this XR 650 stuff. Could this be something simple that I just overlooked, or should I play with different jetting.

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Have you messed with the needle/clip? You should be running an aftermarket airfilter too, Uni in my opinion. Try putting the stock needle in the 4th clip position from the top and turn your fuel screw to 1 1/2 turns out. That should clear some of it up. What elevation are you at also?

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I'm at low elevation, san diego area. The only thing I haven't messed with is the needle. I had read that a lot of guys were leaving it where it was stock. And 1 1/2 turns out on the fuel screw is where I'm at as well. Can anyone explain what would make it idle high for a short time, then go back to normal, without me touching the throttle or anything else?

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Have you checked for mechanical binding? ie... cables etc...

Maybe you kinked a cable or it isn't in the tray it's supposed to run in.

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Another thing that comes to mind. Did you pull the slide?

I pulled mine last night and drilled/shimmed etc... and when you put the slide back in the cut out has to face the throttle valve. It allows the throttle valve clearance to open if not it might bind.

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look carefully for a vacuum leak ... with engine running spray a little WD-40 , or carb cleaner around your carb and manifold seams ... sounds to me like you're suckin' air ... good luck

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sorry,... to be more specific, if your engine speeds up, when you spray the flammable fluid around those seams, you will know it's a vacuum leak ...

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I'll have to check the slide tonight. My old man pulled it out last night, so he might have put it back in wrong. I got the WD-40 suggestion from a friend, too, and will be trying that tonight.

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Disregard lungs post. We're dealing with a 650r here lung not a 650l. Totally different animal. I would also suggest an air leak. I noticed that the 40mm intake boot was not a good seal unless heated up and then torqued on. I would put your stock needle at the 4th clip. The B53 needle goes to the 3rd clip(which is stock). Running on is a sign of air leak or a lean pilot. If you're at sea level and have the 68s you're not lean on the gas. Also pull the pilot jet and blow some compressed air and carb cleaner through it. Backfiring will also happen with a clogged jet, more of a stumble than a backfire, but they are similar symptoms. Good luck.

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Sorry bout the bad info on the slide. :cry: I was trying to help based on what I saw as potential binding problems when I had my L apart last night.

Thanks :cry: TIMBRP :cry: for the correction. I wouldn't want to steer someone the wrong way. :cry:

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Lung it wasn't a "knock" on your part. I just don't want this guy to start shimming and drilling if he doesn't need to. I remember when I was new to four strokes, I took "all" the advice. Sorry to sound harsh, my bad. :cry:

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Not too harsh at all. I would want someone to make sure I was getting the right info.

Take it easy TimBrp :cry:

Chris :cry:

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My 650r is having similiar symptoms, if it is not warm then it will die at low rpms, and it pops when going from high to low rpms. It is pretty new, I only have 60 miles on it since I uncorked it, and 40 miles before that. I live in southern california, typically race at above 1000 ft in warm temp. I am using a B53E needle at the 3 clip and am running the stock pilot. Also, 175 main. If I change to the 68s pilot, will that richin it up a bit? When I get home tonight I am going to try the WD 40 trick, and if that does not work I will begin to play with the jetting. Any suggestions?

Thanks -- Chad Peters

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