high idling on a 400

when I first got this used bike, it had that problem

through inspection, i found out, that the spring on top of the needle, that presses it down, was missing so the needle could jump up/down about one mm, causing uneven idle (normal/high)

now, the problem is back, so are there any other options for unsettled idling

If you have a hot start check its not stuck on,especially if it's mounted on the bars and a cable is running to it.Sometimes the cables pull tight on the frame.It sounds like a air leak?.Check the air filter is mounted properly.Also check for air leaks on the intake side.May be the valves need adjusting.

I had a high idle problem on my WR426 about a year or so ago, but I think it was a fairly isolated incident. It was showing all the signs of an air leak, but even so, it took a few minutes of looking before I found the problem:

A split (actually split in two places) inlet manifold. Worth a look..... :cry:

I would definately check the valves. My yz400 was doing the same thing. Adjusting the valves and re-ringing fixed mine.

Make sure the carb slider isn't cracked. That can cause a high/irregular idle.

Make sure the carb slider isn't cracked. That can cause a high/irregular idle.

Yes, it would be a good idea to check your slide, like Rich says. :cry: Particularly if the throttle stop has been removed altogether, or cut a little bit too short by a previous owner.

#1. I'd do a visual inspection on the Hot Start system, ensuring no air leaks or hoses partly off.

#2. I'd spray some carb-cleaner around the intake manifold to ensure no air leaks there.

#3. If the bike passes both those tests, I'd take the carb off, and check the cables for frays.

#4. Look in the carb for a cracked slide. I think my 400, with a throttle stop that was cut way too short, went through 3 of those damn carb slide plates, and you want to catch it when it is in the "cracked" stage, because shortly after, that thing is going to fracture, and it will send bits of slide plate into the combustion chamber.

Good luck!

Brandon

#4. Look in the carb for a cracked slide. I think my 400, with a throttle stop that was cut way too short, went through 3 of those damn carb slide plates, and you want to catch it when it is in the "cracked" stage, because shortly after, that thing is going to fracture, and it will send bits of slide plate into the combustion chamber.

Is the cause of the carb slide breaking due to the fact that the throttle stop was removed or cut too short? Or are there other reasons the carb slide would break?

Is the cause of the carb slide breaking due to the fact that the throttle stop was removed or cut too short? Or are there other reasons the carb slide would break?

Yes, if the throttle stop has either been removed totally, or cut too short, the carb' slide can 'top out' at full throttle openings, and eventually crack, or in a worst case scenario, shatter the slide. The throttle stop needs to be a certain length, so that it stops the throttle 'wheel' assembly from rotating too far.

could changed bowl float bowl height affect the idle too? cutting supply too fast or too late

just a thought

Yes, if the throttle stop has either been removed totally, or cut too short, the carb' slide can 'top out' at full throttle openings, and eventually crack, or in a worst case scenario, shatter the slide. The throttle stop needs to be a certain length, so that it stops the throttle 'wheel' assembly from rotating too far.

The slide plate on my 400 broke and I did a bit of digging to try to find the cause. The bottom corners broke off of my plate. I heard about the throttle stop theory but I can't see how that would cause the kind of failure I had. My best guess is this: From idle to about 1/4 throttle, the bottom corners of the plate are supported in the slot in the carb body. As the throttle slide wears you get more and more front to back play between the slide and the slot it runs in in the carb body. It moves back and forth with each engine pulse. Above 1/4 throttle the slide and the plate probably pulse together. Below 1/4, the bottom edges of the plate are trapped in the carb body slot but the slide still pulses. I think that's what caused mine to crack. If you look at the bottom of the plate you can see wear marks on the bottom corners that match the carb body when the throttle is closed. There were no marks that matched the carb body when the throttle was from 1/2 to wide open so I don't think the throttle stop is the problem. The wear marks tell me that there is pressure on the plate below 1/4 and I'm betting that's what causes the crack.

Of course, I could be wrong. :cry:

p.s If you're going to replace the plate, make sure to buy a new rubber O ring and install it facing the proper direction. If you put it in backwards it does nothing and Some new plates have failed right away and this may have been the cause. Maybe the reason they break in the first place is that the O ring gives out and can't support the plate.

Mines just gone!!! Exactly the same!

Any ideas where i can get a new plate from?

if its such a big problem they must be east to get hold of!

but i am in the uk :-(

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