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Need help jetting a "BIG GUN"

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I installed a Big Gun Quiet Core with spark arrester a few weeks ago and I can't get it to run. The problem is right on the bottom, If I try to short shift it, it starts breaking up and shakes like a wet dog! Sometimes it even does it on a normal shift, when the rpm's come down between shifting it coughs and stumbles. If you put the engine under a load, like rolling the throttle on, on a moderate hill it misses bad untill the rpms come up. Alittle clutch jab and the bike turns into a rocket. I've tried every pilot from 38 to 48, I've turned the fuel screw between 1 and 3 1/2 out. I've moved the needle 2 notches. I need some ideas to go on anyone have any?? I called Big Gun and they said all they did to they're test bike was go up one size on the main, the main wouldn't effect the power right on the bottom, would it? It seems worse when riding aggressive though really rough terrain.

thanks for any help

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Well after trying to ride again today I've decided it's probably not the jetting, I've tried every possible jetting combo and nothing even comes close, I really can't tell any difference in the way it runs going from one extreme to another with the jetting. And it seems to be deteriorating, it's slowly getting worse. I think it must just be a coincedence that it started doing this right after I installed a new exhaust. So now I'm thinking ignition? ANY IDEAS? I forgot to mention that the bike is a 2005 RMZ with about 7 rides on it,Gett'n pissed so please help before I do something stupid!

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Well after trying to ride again today I've decided it's probably not the jetting, I've tried every possible jetting combo and nothing even comes close, I really can't tell any difference in the way it runs going from one extreme to another with the jetting. And it seems to be deteriorating, it's slowly getting worse. I think it must just be a coincedence that it started doing this right after I installed a new exhaust. So now I'm thinking ignition? ANY IDEAS? I forgot to mention that the bike is a 2005 RMZ with about 7 rides on it,Gett'n pissed so please help before I do something stupid!

here's a start, put your jetting exactly back to stock, change settings one at a time.

after you put it back to stock, put a new plug in it and run it for a while then look at the color of the plug. that will tell you if it's lean or rich. It sounds like maybe a low end lean bog because you said it'll kick in hard if you wait it out. usually it'll die out if it's too rich and you keep adding throttle.

also, try cleaning the carb out, might have gotten something inside there. and have you checked your valves? you should have them checked about 3 hours after you first start riding the bike because of break in time.

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Thanks for the reply!! I've gone back to stock settings as you suggested many times, I've played with the fuel screw , pilot jet and needle to many times to count, it just has to be something else, the big clue here is that it is getting worse, it started out as an occasional slight hesitation, totally ridable though, now it falls on it's face between shifts and won't take just alittle throttle on a hill, its all or nothing, it's unridable. I did take the carb of the bike and look through it, nothing suspect other than it seemed like it fills the bowl with fuel affully high, the fuel is at the top of the brass piece that the fuel line connects to, another words it's right at the rubber hose. I could not find any spec's on this in the manual, any one know? I did try turning the fuel off and riding it, thinking that if it were to high it would lower down and start running better while the fuel level was falling, but it ran like crap right up to when it ran out of gas. I have checked the plug, looked ok, pretty dark but not wet, I think I'll replace anyway. I have not checked the valves though, could that cause these problems? Thats probably a stupid question, I'm going to ckeck them this morning, it's time anyway, if nothing turns up I'm going to drive 50 miles to a freinds house and rob his cdi box and try that, I'll let you know what I find , THANKS

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I have not checked the valves though, could that cause these problems?

yes, if you haven't had them adjusted yet then you should. Most need to be adjusted after about 1-2 hours of initial riding.

Also, if that doesn't help, put the stock can back on and see if that changes, if not, then you can rule out it being the exhaust. I would definately do the valves first.

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Sounds more like ignition problems to me. Valves don't have those symtoms. I have had my CRF 450 intake valves go to .0015 they are suppose to be at .006 So they were completely tight. And it would not run at all. Rode the day before and it ran fine but wouldn't start the next. So if it was valves you wouldn't have the bog and then the surge of power Sounds like the plug my be bad but also I would try your buddies CDI box.

Good luck! :cry:

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