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Discussion Starter · #1 ·
Yesterday i had been riding my 400 for the first time after stripping for powdercoating, it felt way peppier and seemed to pull harder, after riding for a few hours it seemed to choke out at half throttle will not rev as high as it should iam thinking clogged jets but am not 100% help please
 

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I just bought an 01 400ex and I was having the same issue. Well, I haven't had the chance to get it warmed up real good but I noticed that my float bowl gasket is leaking and one of the guys on here, Here 2 help, was a great help with pointing me in the right direction. I have to order my parts but as soon as they come in, I'll get the carb back together and back on the bike and see if that helps. Good luck!
 

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Discussion Starter · #3 ·
mine also will not start and idle unless choked fully...ive tried switching from full choke to none on the fly but it just dies out...
 

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You might get some carb cleaner and check for air leaks or I've seen a few threads on here that your symptoms might suggest CDI box issues. Once I rebuild my carb, if that doesn't solve my problem, I'm trying the CDI box fix next. Truth be told, I was going to change that anyway, so I guess I'm just hoping the carb and CDI gets me running right again haha.
 

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Discussion Starter · #5 ·
i thought it could be electrical because the 3 wires that go into the tailight plug got ripped out b/c a wheelie and i think the wires have touched and shorted my box because it will not rev fully even in neutral or with the clutch pulled
 

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I wouldn't think that those wires would affect how your bike ran and that if they did short to ground, that it would just blow a fuse. That being said, stranger things have happened. Have you taped them up and checked the little fuse block?
 

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Yesterday i had been riding my 400 for the first time after stripping for powdercoating, it felt way peppier and seemed to pull harder, after riding for a few hours it seemed to choke out at half throttle will not rev as high as it should iam thinking clogged jets but am not 100% help please
mine also will not start and idle unless choked fully...ive tried switching from full choke to none on the fly but it just dies out...
Basics please - How long was your machine apart before you got to riding it again? Was the carb drained when it was taken apart?

If it won't idle without choke then the carb needs to be completely cleaned (not spray cleaned), disassembled, immersed, soaked for about an hour in the "good stuff", rinsed in a solvent like mineral spirits or lacquer thinner (I prefer lacquer thinner - it dries quickly and leaves no residue) and all the parts blow-dried with compressed air.

What is probably happening is the pilot jet (idle jet) and/or the air passages associated with the idle circuit are gummed up. When you choke it, the air entering the carb is restricted forcing fuel to be drawn up from the main jet (high speed circuit) enrichening the mixture to promote cold starting. If the idle circuit is clogged, it gets all it's fuel from the high speed circuit. Now if the high speed circuit is partially clogged, it will not run at pretty much any speed unless the choke is on, which reduces the amount of air available.

There are other possibilities which include fuel tank venting, carb float bowl venting, float level, valve clearence, age of fuel, alcohol content of fuel, water content of fuel and eletrical components. It's amazing how just having fresh fuel will affect the performance of an engine.

NOTE: Alcohol will absorb water. When alcohol and water mix, it becomes heavier than the gas and settles to the bottom of the fuel system. It may gel, promote rust and corrosion and clog filters. It may simply displace the gas and the engine is attempting to run on a water/alcohol mix. Engines will run on alcohol, but it takes about a 3 times more alcohol than gas to run an engine without causing damage.

Around here (central Illinois), a vehicle that has set for more than 60 days without being used, needs to have had the fuel system drained before storage and fresh fuel put in before using, to avoid having problems running when next used. In my own machine, I always use premium fuel from a Brand Name source (specifically, I only use British Petroleum which was formerly Amoco which was formerly Standard Oil) and drain the fuel system after every ride. Honda specifies 93 TRUE octane for my engine. Here, we get 89 octane with alcohol which makes a FALSE 93 octane at the pump.

There are many ways to raise octane. Some ways are better than others. For a given fuel, you can raise the octane rating by adding lead, oil, butane, alcohol (methanol, ethanol and isopropyl are all alcohols and their purity "proof" all may vary in percentage) or other chemicals. Japan does not have alcohol in their fuel, so if they specify 93 octane for a given engine, we need to run a 95 to 97 octane here.

I digress - I could go on for hours. Tuning an engine is like baking a cake. For a cake you take flour, eggs, yeast, water, sugar, etc. - put it in an oven at a specific temp. for a specific time and you get a cake. For a motor, if you have suffucient compression, spark, spark at the right time, fuel and air in the right amounts, the engine will run.

I hope the first couple of paragraphs steers you in the right direction. Diagnosing a motor problem over the internet is like trying to have an artist to paint your portrait without being able to see you.

Good luck
 

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Discussion Starter · #8 ·
i never did drain the carb...first mistake.....but i have taken it completly apart and cleaned as you said and dried with compressed air...i have a full tank of gas but it is low grade...machine was apart for aprox a 1-1/2 months. but when it was all back together it ran great for about 2-3 hours then the symptoms i listed started happening. i cut the vent tube on the gas tank to about 3 inches not sure if that would affect anything or not
 

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That's kind of a tough call unless you install an hour meter. I race and as a rule of thumb I began checking my valves every 4th race. After a year, I streched it out to every 6th race. Now, I have settled on an interval of every 8 races. You have to take into account that I may only ride recreationally 3 or 4 times between races.

If you race it's one thing - if you only ride recreationally it's another thing. If you ride 5 days a week it's one thing - if you ride one day a week, it's another thing. How long do you ride when you ride? The races I ride in are typically 2 hours long, so when I ride recreationally, I try to ride at least 2 hours also, but my recreational riding is like race practice, so many times my recreational riding is more than 2 hours and when I ride for fun I ride the same speed as I would in a race.

At a minimum, I would recommend you check the valves twice a year. And checking the valves in the 400EX is easy (screw tappet sdjusters) - mine....... I have remove the cam and change shims. Adjusting the valves in the 400EX usually takes about an hour - my motor requires about 2 hours.
 

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Discussion Starter · #12 ·
Turns out my main jet was loose and that was causing all of my problems...runs great now. What do i use to check the valve clearance? feeler gauges?
 

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I stand by my first suggestion that it was carb related.

Yes, feeler gauges - at top dead center of the compression stroke - in inches, about .003 intake and .005 exhaust. It's best to use two feeler blades, one under each adjuster on the same side of the engine. So you need two 3's and two 5's.
 

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Discussion Starter · #14 ·
Thankyou very much for your help and knowledge
 

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Newbie help

I just bought 2002 400ex and today it wouldn't start. I tried with choke on, no fire. With the middle choke position it tried but still not. I tried without choke and one push on the throttle and it didn't start but backfired. After that series gas started running out. Any ideas wold be appreciated.
 

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First - check the spark - if there is spark, try a new spark plug
Check the compression
If the compression is good and there is good spark, check the carb
If the compression is low - try adjusting the valves to bring the compression up
When checking the carb - first drain the carb and look for water in the gas (with today's alcohol blended fuels - a small amount of water in the fuel will cause the alcohol to separate from the gas and settle to the bottom of the tank and float bowl - the engine will not run on the alcohol water mix, but might fire occasionally) - if no contaminated fuel is found and before pulling the carb, try spraying starting fluid into the airbox and see it will start momentarily - if it does, then service the carb.
More technical, difficult to diagnose problems might be: spark out of time (sheared flywheel key, defective spark plug cap, defective coil or defective stator), defective CDI box or poor wiring connections. If you have been riding in wet conditions, sometimes setting in a warm dry area will cause the problem to vanish.

Good luck
 

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I did as suggested, removed and disassembled carb, soaked it in carb cleaner for an hour, dried and blew it out, reassembled it with the new parts from the Moose rebuild kit except for the pilot screw that i could not remove. Started up, ran about 2 minutes on full choke, then it died. Doesn't Start right up but when it does its only for a few seconds and then dies. Is this possibly all caused by the pilot screw and i will need to buy the tool for one screw?
 
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