2001 400 EX Question

[bsummers12]

I recently replaced a broken cam chain and gear on this quad. I also adjusted the valves to be on the safe side.

Now here is the question/problem. I got the machine started and was at a very high idle but would still rev higher. After a few minutes of the very high idle the exhaust pipes became cherry red. I shut it down and let cool off and re-started, again it became cherry red.

I tweaked around on the carb a little bit and got it started again. But now it seems to use the fuel in the bowl and dies out.

What caused the pipes to become cherry red and now why is it dying out on it's own? What can be done to get this up and running? Also what is the main purpose of the pilot screw and could this be part of the problem?

[Ba9801]

It sounds like the valve timing is off, I would recheck that the chain did not jump a tooth when you put it on.

[GPracer2500]

Certainly sounds like a fueling problem to me, not a valve timing problem.

Assuming the carb is as it should be (jetting is good, no clogged passages) then I'd first suspect an intake air leak. Check all the boots and joints and make sure air isn't being pulled in from somewhere (other than thru the air filter of course).

Is the bowl not refilling? Make sure fuel is flowing from the petcock ok. If it is the carb's float is probably not operating correctly.

As for the pilot screw, it fine-tunes the mixture from 0 - 1/4 throttle. It works in conjunction with the pilot jet. Make sure it's not screwed in all the way because that will cause a lean condition. It should be somewhere between 1 and 3 turns out.


A way too fast idle will make the pipes glow if you just let it sit there with no air moving around it--especially if a lean mixture is causing the high idle in the first place.

If you're not sure the carb is clean and unclogged, just remove it and clean it. Remove the jets, spray all passages with carb cleaner and compressed air (if you have it).

Also, make sure the throttle cables aren't bound up somewhere and make sure it's not as simple as the idle adjustment knob being set wrong.

[timmy400exfast]

it does sound like a jetting problem are you still running stock jets

[bsummers12]

If it was a fuel problem why was I able to get it running twice and now nothing. Unless during the one of the 1st times of running the jet became clogged.

I checked the timing again yesterday and it was TDC. Also tore down the carb and cleaned. There is fuel coming from the bowl when I open up the drain screw.

Now it doesn't even want to fire.

[killer400ex]

everyone freaks out when the heads glow red, this is not un common, remember that there is an explosion occuring inside the motor, it is not allways a jetting issue, i have aftermarket heads and they glow red once it is warmed up too but only if i hold it at a high idol or rev, and make sure you have a full tank and that the petcock is set correctly, and just because it idled high dosnt mean something is clogged, it might just be like mine where you have to set both the idol screw and the throttle cable to get it where you want it, i would set it back to factory specs and go from there, no use in guessing your way through it, it will just take more time and possibly mess up your motor, i wouldnt be too worried, and you might have fouled out the spark plug if you were screwin withthe carb, so that could be a reason it dosnt want to run