Still stumped on the old yz

Okay so I had a post on here I while ago how I was stumped on my 08 yz450 .

Symptoms are that it is a pain to start and when it does it won't stay idling especially when it's cold . It does run pretty rough but it has no pattern so it could be running great then I will turn it off then back on and it will run like a dog . If it will run at all. When cold I usually have to keep it revving and ride it for 5 minutes to get any idle at all.

Things I've done:

Checked throttle cable and hot start have free play.

Checked hot start was not sticking open .

Cleaned carby thoroughly a fair few times .

Swapped pilot jet with a new one and still no good .

Adjusted feul screw

Checked slide plate is in correct position.

Checked valves for leaks and had them sealed again as well as adjusted .

I have checked stator is physically still on.

I am nearly to the point of taking to a shop which is very very un like me but I just can't figure out why I can't get the beast to start well and idle like it should.

Any help would be great ! Thanks

Oh and timing is correct as well

As well as air filter is good and no air leaks and changed plug

It won't run any better with Choke than without as well

Edited by jackiefresh69

Please state specifically what the symtoms are cold and hot.

 

Does you problem go away, or get worse with time

 

Where is your fuel screw set 

 

What kind of fuel screw is it, and is the oring new and in the right order (screw/spring/washer/oring)

 

Have you ever replaced your needle jet (emulsion tube); they oval out and cause all kinds of idle and partial throttle problems

 

Have you done a stator test.

 

Have you done a leak down test ( a real one)

With an '08, the most likely suspect is the stator.  They can develop an internal wiring fault within the coils that will cause intermittent problems such as you describe.

 

However, the idling issue still sounds more like a carb problem.  What kind of response do you get from running the pilot screw in and out?  

 

Read:  http://www.thumpertalk.com/topic/271735-how-to-confirm-your-pilot-circuit-setting/

Please state specifically what the symtoms are cold and hot.

Does you problem go away, or get worse with time

Where is your fuel screw set

What kind of fuel screw is it, and is the oring new and in the right order (screw/spring/washer/oring)

Have you ever replaced your needle jet (emulsion tube); they oval out and cause all kinds of idle and partial throttle problems

Have you done a stator test.

Have you done a leak down test ( a real one)

Okay so cold is hard starting . The. Once it starts it will not idle it will usually just die If I don't keep it revving . From now it gets pretty unpredictable. If you just ride it softly until it gets warm it will run great 50% of the time but the other 50% when you try to ride it will just die out and won't start again . The idle seems to get better when it's hot. But seems to be hanging as well . Like I can adjust the idle screw but then it will drop drop down by itself.

Sorry for bad description I was a Little tired last night hAha

Fuel screw is at about 2 turns out. It is oem and have checked the order and the o ring looks good too.

No I havnt replaced needle jet I will try that.

I havnt done a proper one I might try making one today.

I can't do A stator test atm becauSe I don't have voltmetre but could borrow one of my friend. What exactly am I looking for when testing it?

With an '08, the most likely suspect is the stator. They can develop an internal wiring fault within the coils that will cause intermittent problems such as you describe.

However, the idling issue still sounds more like a carb problem. What kind of response do you get from running the pilot screw in and out?

Read: http://www.thumpertalk.com/topic/271735-how-to-confirm-your-pilot-circuit-setting/

Thanks I will try my best to eliminate the carby today.

Have you properly adusted the fuel screw, for max idle, starting with a low idle, once warm.

So I replaced the needle jet with the one out of my kx250f and now it runs bloody beautiful!!!!! All this messing around the past month just for it to be that. Lol thanks a heaps guys !

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