Problem with idle in 01' YZF 426


I have problem with my never-failing 426 ;-)

The bike never failed till yesterday.

I started it after 3 weeks. First it flood the plug ;-/ I could have happend after 3 weeks of cold weather and beijng started in -2.

"Last time I rode the bike it was -5 a lot of snow and I had graet riding with no problems."

So I've changed the spark plug into brand new and the bike started with 2nd kick (I thought :usuall). But when I've turn off the choke it died. I've pulled the choke agian and start it and I was holding the throttle and turned off the choke. The bike was running but without idle, I had to hold the throttle to pick up revs higher but after few throtle blips it started to hold idle spped (I thought :dirt in starter jet).

So I took a ride but when the bike was really warmed up it stopet on idle and it was very hard to start- 20 kicks and at last it started (with idle setup a little higher).

I arrived home and made fast jets cleaning. Next day I've started it wih no pain and agian after arround 3 km when it was warmed it started to have strange idle. First it was like to high so I simply lowerd idle speed. After next few km the biked died on idle and was agian very hard to start.

I;ve made carb cleaning again (all jets:air and fuel). I've started it with first kick and it was ok but after warm-up it died again on idle and was hard to start.

For me it seems like fuel problems, it works fine with high idle speed (not normal) but when I lower them down it will die when hot.

One more thing after it died on the jurney I started it with many kick and after that it had problems with hard acceleration form low and lower middle revs. It is hard to tell what was going wrong (my english is not enaught) it was something simmilar to missfireing or being to rich.

I,ve never had problems with jetting (winter, summer).

I've checked the valve clearance and it is like it was after rebuild. (new piston, rod, seals, and few gearox parts last year)

New spark plug

Carb seems to be clean after 2 cleanings.

Please help me, maybe it is problem connected with TPS or electrics?

The spark plug connector has few rubber splits but I've never had probles with this.

I don't know what to do.

Please help ;-) Gray where are you ? ;-)

Today I've tried to turn pilot screw in and out , it was a little better but it staled on idle but was a little easier to start.

I've noticed that the exhaust sound on idle is different than before.

Before it was stable and with nice poping sound now it is different, not so stable and sounds like on higher revs and the bikes stalls on idle again after warmup.

my sister-in-law's 350 raptor had this type of problem and in was a faulty gas cap vent. Hope this can help you some how.

I've didn't checked this but I thought it is the problem on high revs but I'll check this.

Any more ideas what to look for?

Maybe an electrical problem, coil or something? But will it be releted with engine temperature and acting almost only on idle?

It sounds like a fuel problem, but that can be clogged jets, bad fuel, weather, an air leak, tight intake valves, incorrect cam timing, etc. All these can affect delivered mixture. Ignition timing is about the only electrical issue that could cause the symptoms you have, and that can be affected by a faulty TPS. The bike can be run with the TPS disconnected as a troubleshooting aid.

Another thing to look at when searching for air leaks is to be sure there is an O-ring on the pilot screw.

Clogged jets-checked 2 times

bad fuel-could be but never had problems with this station

weather -jetting was good in winter and in summer

an air leak, no o-ring on pilot screw-checked,

tight intake valves, incorrect cam timing-checked and thats not this

So bad fuel, vent valve, TPS to check.

Yes, Luckily those are all easy things to do but defintitly try the tps first.

I'll try vent tube test first than TPS. Is it possible for TPS to kill my idle on hot engine only? ;-)

I'm still thinking about carb problems because before the bike loses its idle it has high idle some time before.


Today (at last) I've arrived home and take care of my bike. I've checked the TPS. It had 0,9 ohma on idle possition so too much. I've adjusted it to 0,7 (resistant was 4,89 kOhma *0,14= arround 0,7). I've took a ride and it was ok but I'll definetly try it tomorrow on track. Hope this was the problem.

What do you think.

my wr had a simular problem check that the carb is level and not tilted to on side then knock on carb bowl with wood hammer no too hard think your float my be hung or stuck causing it to starve for fuel just a thought" cost me $70 for my trip to the shop for my hung float

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