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OKAY!! now WHAT IS WRONG WITH THIS BIKE???

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Okay, heres the story

I took apart the top end, and I did not time the cams correctly (bad mistake, I KNOW) so then when I put it all back together I pushed down with my foot, lightly, and slowly, and then I heard it click. The piston touched the valves, and I knew. So I re tore it apart, looked and I did not see anything noticable in bending of the valves (I did not push very hard, very moderate as a matter of fact) but when I realligned the cams and put it all back together, the bike WOULD NOT START and was backfiring and making fire come out of the exhaust quite often.

Please, I would appreciate some guidance. Are the valves bent? Is that what I did? Or is that rare and maybe I should just go back and put in a new spark plug (as it was kinda bad).

The bike is all apart right now, I can upload pics of the valves and see if anyone notices anything.

Thanks a lot

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if the valves are bent I would imagine it would not fire at all

perhaps they are tight? did you replace them? new valves call for diffrent shims.

hows your electrical? cdi working right? plug wire?

and jetting?

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jettings good

it was not new valves, I did not put in anything new.

the valves move fine, but this is bothering me because my bike is in a ton of pieces and the only thing that I dont think is right is that its not starting and the backfiring.

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I had that problem once, bike started very hard, and backfired, throwed flames out of exhaust.. I found that I adjusted timing wrong..

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had that problem with my buddies yz450. turned out timing was a bit off and but the main problem was one of the shims was cockeyed in the spring seat

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I'm going to put my money on that the timing of your intake cam is off one tooth. If you set the timing with the tensioner out, this will happen. You have to double check the timing with the tensioner in, as it takes up any slack in the chain that causes incorrect timing.

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I would agree that if your valves were bent it probably wouldnt fire. But if you want a quick way to check for leaks....take the head off and spray some brake cleaner it each port to see if there are any leaks.

I would also check the shims to see if they are seated correctly, i have seen that happen a few times as well.

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Yes you want to zero in on the problem. If the bike ran fine before the top end was taken apart its most likely not going to be your jetting. I would start with removing all the buckets double checking all your shims, where they are located(ex:intake or exhaust) and then make a note of this. Also make sure the are all installed correctly and not upside down. I actually drew a quick illustration of the head showing this right in the back of the manual when I did it. This way you know whats where for next time. Then redo your timing. Make sure you have the flywheel aligned and check it several times it had a tendency to move on you. I find its easy to atually use a ratchet to rotate the flywheel then when u get it where you need it zip tie to the peg. This will keep it from moving when you start to install the timing chain up over the cams. Then install your cams accordingly(see manual for details). Make sure to check your valves again after the tensioner and chain is installed. Do as you did before and crank through the engine slowly to make sure there is no piston valve contact. Also one side note...if you dissasembled this engine to put in a new piston do not reused the circlips in fact make sure all your rings are correct as well. Also when and IF you inserted the new circlips be sure that you rotate them so the gap in the clip is 180˚ off notch on the side of the piston. If you do not do this the clips can pop out after short run time. Happened to me and almost cost me an engine. Good luck!

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KJ is prop right your probably off by a tooth. Just look close and take ur time. Double check and do it once instead of guessing and doing it 3-4 times.

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Wow, that never really popped into my mind

I will definitely give that a try and report back

Thanks alot I really appreciate the help

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how'd it go? If you don't want to take the cams off you can just check the valve clearances really quick. As long as their within the range you know that isn't the problem. I'm pretty sure it's timing also though.

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Well, like I said at first, I alligned the cams wrong and pressed down on the kickstart and the piston touched the valves.

So I ended up calling a mechanic to see what he would say about the situation and he said that there is a very good possibility that I bent the valves.

So as I was putting it back together, I put on the cylinder head and when I was putting the cams in, I was turning the flywheel, and as the piston would move I could hear a leaking sound. So I'm assuming that I actually did bend the valves and that is why I am hearing this leaking sound.

It just doesnt sound like its sealing, anyone else think its bent valves?

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A bent valve normally will not close all the way. Check your valve clearance and you will find a bent valve quickly, as it will have a clearance much larger than spec. If a valve is bent you probably will not hear a leaking sound when you push it over with your hand, they always make a leaking sound when turned over slow..

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A bent valve normally will not close all the way. Check your valve clearance and you will find a bent valve quickly, as it will have a clearance much larger than spec. If a valve is bent you probably will not hear a leaking sound when you push it over with your hand, they always make a leaking sound when turned over slow..

What e said^^^^

I would say the timing is off, you alrady did it incorrect once, what would make you think you didn't do it right again?

Did you use the correct timing mark on the flywheel?

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