can't get timing right on yfm200
 

The short version of the story is I needed to replace the cylinder head. Now that everything is assembled, I can't get the sprocket to set directly at TDC once the tension adjuster is installed. The TDC line on the cam sprocket either ends half a chain link before or after TDC point on the cylinder. I've strapped the ratchet to the frame so the crank wouldn't move,and I loosened the valve adjustment screws so the rocker arms would be loose. I've also tried setting the sprocket forward TDC by one tooth because I thought it would end up correct once the tension adjuster was installed but it still ended up half a tooth forward.

Any help would be really appreciated. I've been battling this for about 3 days now.

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That is as near as you are going to get so the engine will be OK with that. Highly tuned engines have "micrometer adjustment" so you can get them spot on but a quad engine doesn't need to be that accurate.

:yup: I've worked on a lot of Japanese engines over the years whether they be single or dual cams that you just couldn't get the marks to line up perfectly even if you had a new cam chain and sprockets. On some dual cam models one sprocket mark would be parallel with the cylinder head,the other sprocket mark may be up a little,but as close as you could get it.

Thanks for the feedback. It's had me frustrated since sunday. So I guess the backfiring through the carb is related to air/fuel mix or valves, so i'll tackle that tomorrow.

I've got another question for you guys. If I can't get the timing exactly at TDC, would it be better for the timing to be half a tooth advanced or half a tooth retarded?

Don't think it would matter that much either way,but when I came across one like this, just out of habit I would leave it 1/2 tooth advanced rather than retarded. But that's just me..

Thanks, should I set the valves to standard or leave extra clearance to keep the piston from slapping the valves? I figured I would stab it together, give it a whirl and hope for the best. With the engine being 30yrs old, if it gets ruined so what.

Don't allow any extra clearance. Just set them to specs and go from there.

Thanks for the help. It's still 1/2 a tooth off but runs like a champ, no backfiring and starts easy.

Usually no problems when you get it this close on cam timing. Glad it's running ok for you.