yz450f '06 Stuck at TDC Help!

This afternoon pulled the bike out to warm up and prepped for a morning ride we're going on tomorrow. 1st kick with the choke on she fires right up and i let it run a little before pushing the choke back in...few seconds later dies. 2nd attempt with choke on again starts right up..push choke back in and give it some small throttle chops, no high revs, dies again. Now with the choke out go to kick and when its at TDC I cannot kick it. If I put a little weight on it it will slowly slide then I can kick but as soon as it gets to TDC it stops. What the eff! I pulled out the spark plug and I can kick it smoothly....My guess is a stuck or bent intake valve? Help!

Ask Grayracer. He would know.:thumbsup:

Kind of sounds like it seized up. The first thing I would do is pull the valve cover and check the timing.

Maybe your auto decomp bought the farm:excuseme: Doesnt sound major since you said it kicks smoothly with the plug out. You need to get it started to reset the auto decomp if that is indeed the problem. Im sure its also possible to manually reset it. I just dont know how.

I had a similar problem trying to start mine, the timing chain had jumped.

I pulled out the spark plug and I can kick it smoothly....My guess is a stuck or bent intake valve? Help!

ok think this one through, if an intake valve is bent or stuck why would removing the plug fix the problem? it won't. try this for me. click it up to second and drag it backwards a few feet. does this help? if no, remove the crank plug and put a socket on the crankshaft bolt and spin it counter clockwise. did that help?

sometimes the auto decompression lever will stick and cause what you have described, spin it backwards and it will allow the lever to "flip" and function correctly.

so in summation, when this happens click her up to second and rock backwards a few times.

I meant no disrespect in the first few sentences I just want you to do some critical thinking. (currently raising a 14yo)

Rod

No disrespect taken...Tried in 2nd rocking 3 rounds and no go still bruising my foot at TDC...I'll take the crank plug out and try that next. Thanks for clarifying on the valve deal...it does make sense.

Nothing changed.....

Sounds like the autodecompression mechanism's weight has failed to retract. This happens once in a while if the engine stalls at the perfect time. Most of the time if you put it in gear and bump it forward it will release. Rarely does it stay suck like yours seems to be. Pull the valve cover off and see if it is the weight being stuck out and see if spring on the weight broke or something.

this is the weight on the outside of the cam right...if it is it moves and springs back....where are the dots supposed to be pointed on the cams? It looks like there are 2 dots imprinted on both cams. Maybe the chain skipped a tooth???

Nevermind...there are 13 pins between the marks so it should be aligned properly..It has to be something with the auto decompression. sucks...

Nevermind...there are 13 pins between the marks so it should be aligned properly..It has to be something with the auto decompression. sucks...

Just because the cams are aligned, doesn't mean its in time. Did you check and make sure its actually on TDC when the cams are aligned?....

sounds like the decomp weight or the timing jumped a tooth.

Sounds like the autodecompression mechanism's weight has failed to retract. This happens once in a while if the engine stalls at the perfect time. Most of the time if you put it in gear and bump it forward it will release. Rarely does it stay suck like yours seems to be. Pull the valve cover off and see if it is the weight being stuck out and see if spring on the weight broke or something.

Perfect time,..... you said perfect time (laughing) .......:thumbsup::smirk::usa::busted: :busted:

my 04 had a habbit of the perfect time thing, that's why I suggested the rocking backwards. it always worked.

his advice on removing the valve cover and checking the weight is good info though.

rod

Found out the timing chain jumped quite a bit. Replaced the chain and tensioner and had the valves adjusted just because....she's new again. Thanks

Review the timing procedure in the manual:

http://www.yamaha-motor-europe.com/community/service/manuals.jsp

Basically, with the engine at TDC, the intake cam will have 3 marks visible; E, a dot. and I. The dot should be "straight up", and the I should be at 3:00 o'clock, aligned with the top surface of the head.

Similarly, the exhaust cam should have two dots. These need to be one at 12:00 o'clock, at one at 9:00 o'clock, aligned with the head surface. They will not align perfectly, but if they don't, imagine the mark being on the next tooth over, and see what that would look like.

If you find the cam is out of time one tooth advanced (rotated forward, counterclockwise), that would be the cause of your excessive compression. It might be that it could also be retarded and do that, but it would need to be more than one tooth out.

If you find it out of time, you need to know why. Check both cam saddles and caps for any indication that they may have seized. If they have, you can have the head repaired, so don't let your heart sink to your shoes. If ther is no sign of seizure, and the cams seem reasonably free when CAREFULLY and PROPERLY TORQUED (that's important), the chain and tensioner need to be replaced

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