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2001 TRX 400EX Big Bore 440. Hot Cams Stage 1. K&N Air Filter. 450R front suspension. Pro Circuit T4
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Discussion Starter · #1 · (Edited)
I just got a Niche 440 Big Bore Kit for my 2001 TRX 400EX. I'm having some trouble getting it to idle correctly after jetting. I'll start with modifications made and then go into what I've already done for jetting. Modifications: 440 Big Bore Kit by Niche (newsest part, all the rest have been on the quad before now), Hot Cams Stage 1 cam, refurbished cylinder head, K&N Air Filter with Outerwear Pre Filter, no Airbox cover, Pro Circuit T-4 Slip-On. The rest of the mods are cosmetic, like ITP Holeshot rear tires, 450R suspension, painted black and ProTaper handlebars. I did some reading on this site, and noticed a lot of people went to a 50 pilot jet and to start around a 190 for the primary jet. The quad sounds great when I go over 1/2 throttle just in neutral, but when I get off the throttle, I cannot get it to idle. Any suggestions???
 

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Good luck - idle is the pilot jet, fuel screw and quality of fuel - you should be running 93 to 94 octane non-ethanol gas or 96 octane ethanol blended fuel. Since it has a K&N filter, it may need a pilot jet larger than 50 or you might need to go back to the stock 48. Jetting is as individual as the set-up - what works for one does not always work for another - the fact that it is bored to a 440 has no bearing on the jetting - the jetting is subject to the carb and flow characteristics - the carb is set subject to the intake and exhaust restrictions or lack of restrictions of the engine it is controlling.

Have fun learning how to tune a carb - I quit doing it as I don't have time for it - it requires removing the carb, making changes, installing the carb and testing. Typically idle is the easiest to set unless the intake has been modified and then it's all trial and error till it is right. Do idle first, then work on mid range and finally jet for top end.
 

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Registered
2001 TRX 400EX Big Bore 440. Hot Cams Stage 1. K&N Air Filter. 450R front suspension. Pro Circuit T4
Joined
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2 Posts
Discussion Starter · #3 ·
Good luck - idle is the pilot jet, fuel screw and quality of fuel - you should be running 93 to 94 octane non-ethanol gas or 96 octane ethanol blended fuel. Since it has a K&N filter, it may need a pilot jet larger than 50 or you might need to go back to the stock 48. Jetting is as individual as the set-up - what works for one does not always work for another - the fact that it is bored to a 440 has no bearing on the jetting - the jetting is subject to the carb and flow characteristics - the carb is set subject to the intake and exhaust restrictions or lack of restrictions of the engine it is controlling.

Have fun learning how to tune a carb - I quit doing it as I don't have time for it - it requires removing the carb, making changes, installing the carb and testing. Typically idle is the easiest to set unless the intake has been modified and then it's all trial and error till it is right. Do idle first, then work on mid range and finally jet for top end.

Yeah.... the 185 was way too high. Machine went into hydro lock due to running too rich. Going to come down the 170 and see how it runs then. Still won't idle or start clean, we'll see how changing the main goes.
 
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