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Discussion Starter #1
Greetings everyone! I am working on my 2005 trx400ex. I recently had a 440 big bore kit installed. The bike will crank for brief moments and barely idle. If I try to throttle it, it bogs out and is difficult to restart. I was told I need to rejett the carb, if so what jett kit should I use? Thank you!
 

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I have a hmf main and honda 42 slow jet in mine, runs fine. I’ve been told to stay away from dynojet. Keihin is what most people prefer


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Discussion Starter #4
I tried the 42 slow jet, it idled but kinda high. I tried to adjust the fuel screw but it sat all the way down. What size is the hmf main
 

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The kit was 1st put on with just the piston and cylinder. It ran ok. I had the entire top end rebuilt and now it seems as the carb won't keep it running
 

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If it ran good before the rebuild chances are the "rebuild" wasnt done right. My bet is its a tooth off on timing. Carb tuning will make it run crappy. But to go from running to not running i would find it hard to believe the carb went bad at random. Unless the topend rebuild took a few years or something and the carb could have gummed up.
 

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I tried the 42 slow jet, it idled but kinda high. I tried to adjust the fuel screw but it sat all the way down. What size is the hmf main


I have a 165 in it, might need a 170. What works for me might not be the best for you though.


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I cleaned the carb and went back with the 38 slow jet, now it's idling and running perfectly. Nothing smoking or leaking.
 

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Glad you got it figured out. But i forsee a blown headgasket in your very near future. There is 100% no way that 38 pilot jet is giving a 440 enough fuel at idle. I would bet my last dollar if you start it and let it idle the head pipe will be cherry red in no time.
 

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You sir might be psychic! Lol I think thats whats happening now. It ran perfectly yesterday, I rode it a bit more and now it's idling high again at times and my exhaust pipes seem to be getting hotter than normal
 

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Discussion Starter #11
So with that 42 slow jet is it supposed to idle a little higher? The higher idle is why I went back to the 38. Does this mean I'm running too lean? I really appreciate y'all taking the time to respond to my remedial questions!
 

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Nope just been building 400s for a very long time. The pilot jet is what fuels the motor at idle. It is metered by the mixture screw. That is gunna be why your idle is goofy. Mixture screw setting isnt correct. Im gunna bet with a 440 kit your gunna want a 45 pilot jet. I put the 42 on everything from bone stock to 416s with pipe and filter. The 42 pilot jet honestly if it wasnt for emissions regulations would be the better jet for honda to use from the get go. They are in all honestly lean right out of the box. The proper way to set your mixture screw is on the quad with it running with a 90° screw driver. You are looking for the highest idle you can get. If that setting is around 2 turns out and less than 3 your good. Anything more then 3 it needs a bigger pilot jet. Anything less then 1 1/2 it needs a smaller pilot jet. My bet is you have the idle turned up higher then its supposed to be and your idling off the needle and mixture screw. That is gunna be a real inconsistant idle. Btw. No ones questions are remedial. We are all here for the same thing. Learn and pass on knowledge. We are always glad to help!
 

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My head pipe very slowly starts to turn faint orange at idle but I think it’s because it’s aftermarket stainless. 30 seconds of riding and it cools off. This is on a 416 with 42 pilot. Does yours do that slammedranger? I know we have the same head pipe


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Nope. Put a 45 in it. I was running a 45 with a very similar setup. Where is your mixture screw set at also?
 

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Took me a while to remember to check. It was about 3 and 3/4 out. Ordered a 45 slow jet lol


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