my WR 400 wont idle. Im about to light it on fire.

Alright so I have a 99 wr400.

This thing has always run like a champ.

It still has great power and runs tits minus the fact that It will not idle at all.

The problem started out at my last desert trip about half way thru the trip.

Since then i would say it has definately got worse as it seems it will not even idle on its own for more than 2 seconds.

Now this bike would usually start first kick unchoked stone cold and go right to an idle.

It will however idle a little if it's fully choked. but it does not go into a "high idle" like it normally would.

So far I have checked the idle jet, cleaned it, replaced it.

cleaned the ever living crap out of the carb about 5 times now.

Replaced the spark plug

Replaced the intake boot as it had some minor cracking.

Checked the valve lash. (it was spot on factory spec) surprising considering this is a 16,000 mile bike and they've never been touched.

And get this. I even took the carb off my neighbors wr and put it on my bike, and put mine on his bike.

His bike ran fine with my carb and my bike did not improve from putting his carb on my bike.

Im starting to get stumped here and wondering what could be wrong.

Anyone have any ideas?

Thanks!!!

-Donald

Spark plug

Spark plug

OP said he replaced it in the original post.

I'd head electrical. You have a mate with an identical bike so this will be easier: swap coil, CDI and stator in that order. But swap one, then both you run your bije and see where you end up. My guess is coil or CDI. But you must have the same bike series 400/426 or 450 to try swapping electrical stuff.

Report back!

Edited by miweber929

right on. I will give that a shot.

His bike is at my house now.

I better get on it quick because i know he wont like the idea of taking parts of his bike to try them on mine. he was VERY uneasy about the carb swap as it was.

but hopefully i can pull it off discreetly while he is at work :p

ok so coil swap and cdi swap showed no improvement.

Is anyone thinking it could be an air leak? ie valve not sealing. or something like that.

To me it acts like its running lean and always backfires through the air box before it dies.

ok so coil swap and cdi swap showed no improvement.

Is anyone thinking it could be an air leak? ie valve not sealing. or something like that.

To me it acts like its running lean and always backfires through the air box before it dies.

You said you checked valves, but did you check timing is correctl? Big rash of jumped timing WR400's on here lately, since it doesn't seem carb or electrical I'd check that.

Also try a compression check to see if a valve is leaking as this bike shouldn't have the auto decompressor.

May be an air leak, check intake boots and air box path for leaks as well.

cdi box checks out.

coil checks out.

plug is new.

head is off

took it to yami dealership. mechanic said valves were not burned and had good seal.

all the dots lined up at tdc on the cam sprockets upon disassembly.

the only problem was that the "I" tdc mark was all the way to the left of the site hole when the cam sproket marks were lined up.

I cannot see how it could be jumped timing as this is a problem that has gotten slowly progressively worse over the past couple months.

the only thing that hasnt been looked at yet is the actual cdi pickup on the flywheel or whatever.

Bad cam chain tensioner and worn out chain.

cdi box checks out.

coil checks out.

plug is new.

head is off

took it to yami dealership. mechanic said valves were not burned and had good seal.

all the dots lined up at tdc on the cam sprockets upon disassembly.

the only problem was that the "I" tdc mark was all the way to the left of the site hole when the cam sproket marks were lined up.

I cannot see how it could be jumped timing as this is a problem that has gotten slowly progressively worse over the past couple months.

the only thing that hasnt been looked at yet is the actual cdi pickup on the flywheel or whatever.

Bad cam chain tensioner and worn out chain.

+1

This all should line up if everything is correct, stretched (or stretching) cam chain and tensioner sounds like your issue. It's not real expensive (compared to bent valves and a busted piston) and good maint anyway.

My call at least. Can you shoot a pic of what you are saying? If it's "slightly off" you should still run right; if its out of the little window notch, yup, replace.

OK thought I would update this.

Finally got the bike back together today and went for a test ride.

It's night and day better from when I tore it down, however, it still only idles for about 20-30 seconds then dies.

This is an improvement because it basically would not idle on its own at all before.

I tore it down and replaced piston, rings, cam chain, and flywheel. Also put in a brand new spark plug.

Im definitely a step in the right direction, but now Im wondering where to look next to get this thing back to 100%

Carb emulsion tube (needle jet) and pilot jet and fuel screw

check all the wiring from your stator/cdi to the plug. A bad connection could cause this. Pull every connector off and clean it out really well. check for any rubbed wires etc.. good luck

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