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Discussion Starter · #1 ·
Hi, I have 01 440ex, i have a question about the jetting. I have a 165 man and a 38 pilot, doesnt seem to have much power in the midrange and up and carb is squeaky clean, i dont know if these are stock or what have you. any assistance would be appreciated on where to start, my machine has a weisco 440 bbk, FMF megamax exhaust (stock head pipe) and the air box cover is ON, running regular 93 pump gas, please help me out...:confused:
 

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Discussion Starter · #3 ·
k&N and im actually running half 93 half c-12 , i checked the carb and it has a 165 main and a 38 slow jet, really breaks up past half throttle, what should the mixture screw be set at? i was thinking 1 1/2? thanks for the response
 

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Mixture screw is for idle only - 0 to 1/8 throttle

Dump the racing fuel and try straight high octane pump gas. Your engine is probably not designed to need 98 octane (appx. 50/50 108 c-12 and 93). If that dosen't work, then drop the main jet.

Since you revealed the true fuel mix, my guess the fuel is burning too slow and the speed of the piston is getting ahead of the flame front. Dropping the octane (faster burning fuel) might fix the problem without any other changes.
 

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Discussion Starter · #5 ·
pk, so went down to a 155 main jet and adjusted fuel screw to 2 1/2 turns out, runs like crap, but if i pull the airbox lid off it runs better but runs really lean, i'm losing my mind on this 400ex what am i missing here?:mad::mad:
 

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Start over - how does it idle? Adjust the fuel screw for a smooth idle at operating temp then leave it alone. Since it runs better with the air box lid off, it is getting more air and it leans out. Your mixture is too rich or the octane of the fuel is too high.

Good luck. Jetting can be a bitch even for a seasoned tuner.
 

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Discussion Starter · #7 ·
I dont have the ability to tune the pilot screw with the engine running, its directly on the bottom i've tried a 90 degree screwdriver and it didnt work.( unless someone knows another way) i've NEVER had an idle problem, idles nice, but falls on its face when you rev it up, I had it running really good yesterday but the plug was chalky white so i knew WAY to lean! should i run 87 or 93 in this? the dealer says to run the c12 I have, I told him yea right it runs horrible.I guess I have a dynojet kit in it, the dealer found out. He gave me a 150 and 155 main, Which should I use? thanks for the help
 

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There is a "flex jet" screw available for about $35. It has a knob and a flexible shaft (like some idle screws) and you can adjust it with your fingers. Use 92, 93 or 95 octane. Lean is hotter burn and more power - just don't get so lean that detonation occurs. Detonation will burn a hole in the piston.

If it "falls on its face" when you rev it up, have you checked the accelerator pump operation? Sounds like it might not be working. May need adjusted or repaired.

Awhite plug is not necessarily "bad". Unleaded gas burns clean. If the mixture is right, you will have to run for about an hour at high speed to get a light color. If the mixture is too rich, it will turn the plug black in 10 to 15 minutes of on and off the gas riding.
 

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Discussion Starter · #9 ·
ok, so i put 93 in the tank and adjusted my pilot screw to 2 1/2 turns and it noticeably runs ALOT better doesnt stumble anymore, so thanks, but im confused on the plug it has a brown ring around the plug , porcelain is a brown with black specs and the electrode is like a blue color, is that all ok?
 

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Sounds about perfect - my 250 ran the factory spark plug for 8 years before I had a problem and changed it. Just so happens I went from BP to Shell gas the same day. First I blamed the fuel, I looked for water in the carb, finally I changed the spark plug and it started running right again. I'm not saying Shell gas was the cause of the problem, but is is possible that if I had not changed fuels, that I might still be running on that 8 year old plug. Anyways, I'm going back to BP gas.

The old plug that came out (after 8 years) was a light tan on the porcelain, blue on the electrodes and a dry dark grey to light black on the inside of the threaded jacket.
 

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If the only change is the air box lid - I would try it first without rejetting - if it seems to need a bit more, then go up just one size, whether it be a 157.5 or 160. No other changes should be necessary.
 

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Discussion Starter · #14 ·
I have noticed my 400ex choke keeps opening up all the time, just started doing it, I have seen there are many tutorials on how to completely remove the choke and replace the pilot with a 42. well, instead of dealing with the honda guys around me i went to yamaha and they gv me a 42 pilot for my carb, screws right in nice and light same thread. BUT its a few mm longer, will this matter? do i need another jet?
 

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If it was the right "style" of jet, it would be the same length, shape and diameter.

If it was the wrong style - there is no guarantee that a number 42 of one style of jet is the same as a number 42 of another style of jet.

Even if you remove the choke, changing the jet does not actually compensate for the modification. It would be more cost effective to get the choke repaired.
 
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