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Hi Guys! I see that this is an old post but i really need some help with my quad. I have a 1999 Honda 400ex that has been bored over to a 440 with stage 2 hotcams. I also have a pro circuit exhaust and a Uni air filter. I am having the same issue as many of you where it will start up and idle fine, but when I rev it up it spits and sputters. It also misses a little when its running. Right now i have a 190 main jet and a 55 slow jet, and the mixture screw is 2 1/2 turns out. It seems like it is running a little rich due to a brown/blackish plug, but it also seems like its not getting enough fuel. It does not smoke at all when it is running, just the little bit of white smoke when i start it up. My compression is at 120 psi. If you guys have suggestions PLEASE let me know because this quad is driving me crazy.
 

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2020 520 rubicon foot shift
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If it spits and sputters its too rich.
I went through this years ago with mine, a local tuner/pro motor builder told me how to set em...
Jet it rich enough to sputter (your already there) then go one step leaner at a time until it runs clean, once its run clean its jetted right. So you need to go 1-2 sizes smaller on the main and test ride it, if it runs runs good your done, if not go 1-2 sizes smaller again then test ride it again.
I could change the main in my 400ex in a couple minutes, take the 17mm bolt out of the carb then put a short 6.5 mm socket in a pair of pliers and change the jet.
PS my 440 kit with a stage 2 hot cam, ported head and white brothers slip on liked 38 pilot, stock needle and 165 main with the air box lid on and a 175 main without the air box lid. Dont go straight to these settings tho, work your way towards them, mine was leaner than most but also faster, it smoked stock 450's. The guy who built it also built the fastest pro race quads around at the time.
 

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Thank you so much for your reply! I see what you are saying that it is too rich. I am running a Chinese stock replacement carburetor with a 190 main and a 55 pilot jet. When i got the quad it had stock jets with all the upgrades that i had and it still seemed to be fouling out the plug and bogging. So i just assumed that more engine meant more fuel so i got bigger jets. I can now see that jetting is gonna be a bitch. It seems like you have the exact same upgrades as me but you have porting done. What sizes for jets do you recommend me get to start off?
 

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2020 520 rubicon foot shift
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I'd try a stock pilot, stock needle and 180 main first, then go leaner if need be.
My 440 was a bitch to jet as it needed leaner jets then when I had just a slip on, I didnt expect this and learnt alot dialing it in.
Bigger motors make more vacuum than stock so they suck more gas through the jets than stock. A prime example of this is 250 and 300cc two stoke bikes, they're the same except for the bore and the 300 has smaller jets in the carb.
 
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