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ThrakenH04

Valve and stroke question

7 posts in this topic

Ok well, I can re-shim the valves to get correct clearences but I think I put it back together on the wronge stroke. Here's the symtomes(spelling?), It takes about 3-5 kicks when its cold to get it started and even more if I had ran the gas out of the carb on a previous run. The problem is, when the engine is fully warmed up it likes to stall, and when I try to start it, I can sometimes kick 2-3 strokes before getting to the TDC compression stroke. What I need help with is, how many strokes do I turn back or foward to get things back on track? Sorry if it doesnt make any sense. I need to know soon too, I have practice on saturday and sunday.

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There is no wrong stroke. The cams are what makes the difference between TDC compression, and TDC exhaust /intake. Since the ignition triggers on the crank, and produces a spark on every revolution, it simply doesn't matter. Any TDC becomes the right stroke when you time the cams right.

Go back and check your valve clearances and your cam timing. If your exhaust cam is retarded, the decomp mechanism will let off almost all of the compression stroke. A tight intake will cause an erratic idle in addition to lack of cranking compression.

Be sure your fuel mix is set right at idle, too.

BTW, if your spelling worries you, the spell checker below the post window works.

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There is no wrong stroke. The cams are what makes the difference between TDC compression, and TDC exhaust /intake. Since the ignition triggers on the crank, and produces a spark on every revolution, it simply doesn't matter. Any TDC becomes the right stroke when you time the cams right.

Go back and check your valve clearances and your cam timing. If your exhaust cam is retarded, the decomp mechanism will let off almost all of the compression stroke. A tight intake will cause an erratic idle in addition to lack of cranking compression.

Be sure your fuel mix is set right at idle, too.

BTW, if your spelling worries you, the spell checker below the post window works.

The problem is, lining the dot and the other dot. The thumperFAQ shows one thing, then my manual shows another. I kinda wish There was someone I knew with a 03-05 YZ450 that could show me a picture of where the correct timing marks should be on the cams. Sometimes I wish I had a SOHC.

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Here's a link to a pic showing the cam timing marks at TDC (compression stroke).

Cam timing marks pic

This pic is a 250F but the 450 looks the same. Notice the timing marks on the outside of the cams (9 o'clock on the exhuast cam and 3 o'clock on the intake cam) are lined up with the top surface of the head casting.

Here's some other pics showing the position of the cam lobes at TDC (compression stroke). This pic is also a 250F but once again, the 450 will look the same.

Cam Lobes Pic1

Cam Lobes Pic2

Cam Lobes Pic3

Hope this helps.

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