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LongLiveTwoStrokes222

06 YZ450F Hesitation and Coughing

9 posts in this topic

So I got a 2006 YZ450F and Im kinda new to the whole four stroke thing and I have done everything to try and get rid of this hesitation when the throttle is cracked open. And it also pops and stumbles when the throttle is held constant no matter the throttle position. I have tried different pilot jets with no change and I know its the right size because the fuel screw is out 3 turns. I moved the needle up and down two positions and it did nothing either. Cleaned the carb and set the float height to the correct height and still nothing. Ive tried the fuel screw in and out and neither helps. New spark plug and its jetted like perfectly according to the color. I also put in a new needle holder in and the slide plate and seal are good. Made sure the float needle wasnt stuck and that the floats didnt have stuff in them. I cant figure it out for the life of me Ive searched all over the forums for like 3 weeks every day and cant find anything. I did find one person that said that the reason these bikes are jetted so lean on the pilot is because the AP squirt is huge. I checked and it does work and the squirt is huge. So the guy said that if you try and make the decel popping go away with a richer pilot that it makes it crazy rich at the crack of the throttle but mine does it anywhere between 1/8th of a throttle to WOT when the throttle is held constant. If I just open her up it runs perfect. Oh and I forgot to mention that I tried unplugging the TPS as well and no change. This all started after one day I was warming up my bike to go riding and I let it get warm and gave it a rev and it the rpms went up and it made a big pop like a backfire and died and then it would not start even hill starting it. Then I tried one last time to hill start it after I kicked for 15 minutes and it started and ran like crap and would only stay running if I gave it gas. So I thought must of jumped timing checked it and sure enough it did. Reset the timing and checked valve clearance while I was in there and every valve was in spec. So I put in a new spark plug and put it together. Started first kick and had WAYYY more power than it had when I bought it but then this crap started happening. The one thing I havent checked is my timing to see if I had it wrong by one tooth or so. But i would thing that would make it run like crap everywhere. And I dont think its jetting cuz nothing I change jetting wise helps or makes it worse. Any Ideas?

Edited by LongLiveTwoStrokes222

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Timing jumped and you did not replace the cam chain and tensioner?

No I am planning on getting a new timing chain tho. I was just going to ride it for like a week till I had money to buy a new one. But why do I need a new tensioner? It doesnt wear out.

Edited by LongLiveTwoStrokes222

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Slide plate is installed upside down

It's installed the square side down the side with the hole. Thanks for the suggestion tho I didn't even think about that.

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I almost never replace the tensioner because almost nothing ever happens to them to warrant it.  It is easy enough to check the condition of it, though, and they're only $40 or so.  Don't ride it again with that timing chain, however.  Stiff links?  Thought so.

 

Have a look at the hole in the top of the main nozzle.  If it shows any signs of wearing into an oval, you need a new one; it will mess with the part throttle jetting.  

 

To baseline the jetting on an '06, I'd start with a 45/168, and the standard NFPR needle, clip in 4.  An NFLR needle works well, too.  If it has an aftermarket needle, try replacing it with an OEM part.  

 

Stators can cause this kind of thing as well, but the symptoms are normally different.  Nevertheless, check to see if it's loose on the case cover, and when doing the resistance checks, rap on the cover with a screwdriver handle to see if the needle jumps around due to a broken coil. 

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I almost never replace the tensioner because almost nothing ever happens to them to warrant it. It is easy enough to check the condition of it, though, and they're only $40 or so. Don't ride it again with that timing chain, however. Stiff links? Thought so.

Have a look at the hole in the top of the main nozzle. If it shows any signs of wearing into an oval, you need a new one; it will mess with the part throttle jetting.

To baseline the jetting on an '06, I'd start with a 45/168, and the standard NFPR needle, clip in 4. An NFLR needle works well, too. If it has an aftermarket needle, try replacing it with an OEM part.

Stators can cause this kind of thing as well, but the symptoms are normally different. Nevertheless, check to see if it's loose on the case cover, and when doing the resistance checks, rap on the cover with a screwdriver handle to see if the needle jumps around due to a broken coil.

That jetting is exactly what was in it when I got. So I'm going to put the 45 pilot in and I checked my timing and it was by one tooth on the intake. So today I'm getting a new cam chain and throwing back together and I'll give you an update. Thanks!

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I almost never replace the tensioner because almost nothing ever happens to them to warrant it. It is easy enough to check the condition of it, though, and they're only $40 or so. Don't ride it again with that timing chain, however. Stiff links? Thought so.

Have a look at the hole in the top of the main nozzle. If it shows any signs of wearing into an oval, you need a new one; it will mess with the part throttle jetting.

To baseline the jetting on an '06, I'd start with a 45/168, and the standard NFPR needle, clip in 4. An NFLR needle works well, too. If it has an aftermarket needle, try replacing it with an OEM part.

Stators can cause this kind of thing as well, but the symptoms are normally different. Nevertheless, check to see if it's loose on the case cover, and when doing the resistance checks, rap on the cover with a screwdriver handle to see if the needle jumps around due to a broken coil.

and I put a new nozzle in it

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