2002 trx400ex jetting - Honda TRX Forum
 
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post #1 of 4 Old 09-14-2016, 03:12 AM Thread Starter
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2002 trx400ex jetting

I have a 02 Honda trx400ex I just rebuilt it still has a stock top end and bottom end it has a FMF titanium core 4 slip on and a FMF header and an aftermarket intake box that has all of the wires and battery stuff relocated into it. It has a cover and the stock snorkel on it and would like to keep it that way to keep dirt and mud off of the electronics. It idles good and runs good just cruising around but cuts out at medium to full throttle position when reall riping on it. When I had first got it it had a stock air box with no cover and the slip on had the wrong adapter on it to fit the header so I fixed that and now every thing is leak free. The guy I bought it from said he thought it needed to be jetted but wasn't sure. Is there a way for me to know what jets are in the carb and what do you guys think I should be running for jets with the setup I have. It also needs a valve adjustment has a slight tick.

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Charlie
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post #2 of 4 Old 09-14-2016, 02:18 PM
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You have to take the carb off to look at the jets and see what # is stamped on the jet - this works if the jets haven't been drilled out. What you say about idling and running fine up to mid-range tells me the pilot jet is fine and the slide needle setting is OK. When you say it cut's out on the high end, it could either be too rich, too lean or have an ignition problem. You have to figure this out by experimentation. Try running with the top off the air box - if that makes it better, it's too rich - if it makes it worse it's too lean - if there is no change, it might be ignition (try a new spark plug).

Changes to the exhaust do not always require rejetting, but changes to the intake almost always require rejetting for the high end. If you don't have a flow bench and fuel/air ratio meter, you either have to ride it, make changes, ride it again and repeat the process till you have it right, or put it on a dyno, run it, make changes and run it again till you get it right.

A slight tick does not always indicate need for a valve adjustment - the cam chain usually makes more noise than the valves and piston slap makes more noise than the cam chain. A slight tick means the engine is running - it's an air cooled engine - it does not run silent, minor ticks, whines and buzzes are somewhat normal - modified engines make more noise than stock engines.
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post #3 of 4 Old 09-14-2016, 10:10 PM Thread Starter
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With air box cover off it runs like a top. What should I do if I want to put the air box cover on?
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post #4 of 4 Old 09-15-2016, 03:26 AM
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Smaller main jet - about 4 sizes down from whatever it has in it now
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