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pjmetro

YZ Cam, won't start

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I just installed a YZ exhaust cam in my 05WR450, I lined up all the timing marks to stock WR setting. The valves didn't need adjusting. But now it won't start, it just backfires. Any ideas?

Thanks, Paul

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im registering my interest in this topic

i too have wondered if the yz cam would work with the e-start since it has a shorter decomp pin (kick start really doesnt need so much decomp)

will it kick start?

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No , It won't kick start. I did have the whole motor apart at the same time I did the cam (had to replace the left side of the case). Is it possible that I'm on the marks but 180 out on the crank?

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No , It won't kick start. I did have the whole motor apart at the same time I did the cam (had to replace the left side of the case). Is it possible that I'm on the marks but 180 out on the crank?

I have wondered about the crank being 180 before, and used what noodle I have left to determine that the crank and piston dont really care if they are 180 degrees or 360 degrees as long as there not hooked up to the cams. Once you hook the crank to the camshaft, it will determine if your at TDC compression stroke, or TDC exhaust stroke.

The only problems I remember reading about was that you cant turn your wr auto decompression cam to yz timing cause it would screw the decompression. But putting in the yz cam sounds right :applause:

So you need to check your cam timming. It isnt right :D

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What do you mean by stock WR setting? If you timed it by counting pins then your timing is not correct on the exhaust stroke. If you have indeed installed the YZ cam then you need to set it to YZ timing. I'll bet you have your timing off by one tooth. Hope this helps.

Josh

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I have wondered about the crank being 180 before, and used what noodle I have left to determine that the crank and piston dont really care if they are 180 degrees or 360 degrees as long as there not hooked up to the cams. Once you hook the crank to the camshaft, it will determine if your at TDC compression stroke, or TDC exhaust stroke.

The only problems I remember reading about was that you cant turn your wr auto decompression cam to yz timing cause it would screw the decompression. But putting in the yz cam sounds right :applause:

So you need to check your cam timming. It isnt right :D

I'm unsure myself but isn't the ingition timed from the crank? If so, If it were 180 out there'd no fire when you need it.

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I'm unsure myself but isn't the ingition timed from the crank? If so, If it were 180 out there'd no fire when you need it.

NOPE! Fires every stroke as far as I know! It is true that the crank does not care what stroke you are on that is determined by the cams! everybody here sounds spot on,one tooth off!

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NO, it fires once for every 2 crank rotations. {might spark on overlap but that isn't firing}

that would be it firing every 4 strokes not every 1.

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Simon, Thanks. It sounds like it is off one full rotation on the crank then. I will pull the cams, rotate one turn on the crank and reinstall the cams on the timing marks. I will let you all know how it works.

Thanks

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Well I tried rotating the crank one full turn, No change. Then I tried Leaving the intake cam on it's mark at TDC and rotating the YZ ex cam one tooth clockwise. No change. So my question is what is the right timing for a WR with a YZ exhaust cam?????? :applause::D:prof:

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And I will say again that the crank does not care what stroke it is on!!!!!!You can set the cams one way and then spin the crank 360 degs and it will be the same!!! When I said it fires every stroke I thought everybody knew I was talking about the PLUG! Of course it does not make squeeze and power on every stroke! :applause:

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Well I tried rotating the crank one full turn, No change. Then I tried Leaving the intake cam on it's mark at TDC and rotating the YZ ex cam one tooth clockwise. No change. So my question is what is the right timing for a WR with a YZ exhaust cam?????? :applause::D:prof:

I have never put a yz cam in a wr but I have run my wifes 01 wr 250 with yz timing.If you tried one tooth retarded you might try one tooth advanced (the other way) Be very careful while playing around like this!Maybe go as far as pulling the plug and spinning it over by hand till you are sure that everything clears!!!!

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Thanks, I wasn't doubting you on the every rotation thing, I just wanted to try. I will try retarding it one tooth to see. I know I'm not the first to rum a YZ cam, so I would like to get some input from someone who has already done this.

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I have YZ cam's in my 05 WR450. i just lined the marks up on the head and it fired right up with the electric start. I did rejet the carb to a 170 main, and raised the needle one clip.

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I believe that you said you have the manual. Forget for a minute that it is a YZ cam and just follow your manual. The alignment will be exactly the same. There are two differences in the WR and YZ exhaust cams after 03. The location of the timing marks and the location of the decompression pin. Have you checked to see if you have any spark? You may be chasing your tail for a problem that isn't even related to your cam swap. Hope this helps,

Josh

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Yes I do have Spark. But at this point I don't think the cam is the problem at at, Because I just put the WR cam back in, the backfire is gone but it still won't start.

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If you are putting a yz cam in a wr motor: use the timing marks on the yz cam and line the outside ones up/level with the head casing, as the timing marks are already set to yz. If you turned it one tooth clockwise you have retarded to timing to far. If you turn it one tooth counterclockwise, you will be back at the wr timing.

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. Forget for a minute that it is a YZ cam and just follow your manual.

^what he said!!!!!!!

just use the mark on the cam gear.......

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