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Evening! I am running in to a bit of a debacle and it's seriously driving me crazy. Last year I got a used 08 yz450. My coworker recently gave me the exhaust cam from his 06 that I decided to throw in there. I also put in a new plug and changed the jetting. Here is where I am running in to my issue (three times in a row now). As soon as I get it buttoned back up, it absolutely will not turn over. 

My marks line up on the cams and TDC (checked through the spark plug hole to make sure it was top and not bottom). 

Cam chain seems to be fine. 

I can not find anything else that is out of the ordinary. What the heck am I missing here?!?!?

 

edit: before I put in the spark plug I can turn it over by hand no problem via the kick starter. No weird noises or binding, nothing, totally normal

Edited by SomeSortOfThing

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12 minutes ago, Krannie McKranface said:

Why did you change the jetting, and what did you change...

Trying pro circuits recommended. Changed the needle (NFLP I think?) and leaner on the main and pilot 

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27 minutes ago, SomeSortOfThing said:

Trying pro circuits recommended. Changed the needle (NFLP I think?) and leaner on the main and pilot 

Without getting specific on the jets it will be difficlut to get any help here....

It sounds like your pilot is too rich, so it won't start. Try going in on the fuel screw a full turn.

Also, if you can't start it in 6 -10 kicks, normally, you need to clear the cylinder before continuing to try and start it (wide open throttle, kill button depressed, kick  through several times)

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Pilot I went from a 48 to a 42. When I mean it won't start, I mean I can't even kick it over. I just went out there again and took the plug out no problems whatsoever. As soon as the plug is in I can literally stand on the kick starter and there's nothin

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The exhaust cam has a decompression release. Either the decompression release is damaged on the 06 cam or incompatible. One of the two

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The '06 ex cam is compatable.

But yeah, it sounds like he decomp is not working.

More than likely your cam timing is off, so the decomp is occuring too early.

Edited by Krannie McKranface

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My understanding is the 06 cam in 08/09 motors is supposed to be the cats pajamas. Is this even true? That's why I put it in there in the first place. 

 

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That's what I've heard in this forum also but they are different part numbers and you are having problems with the different model year cam so there's that. What was wrong with the 08 cam

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13 minutes ago, Masterpeen said:

That's what I've heard in this forum also but they are different part numbers and you are having problems with the different model year cam so there's that. What was wrong with the 08 cam

Nothing. I got this one for free so I figured I would try it. Maybe I'll throw the other one in after work and see if it's the cam or user error lol. 

I guess another question I thought of since timing was mentioned... When I'm looking through the check hole the markings look like |-|| (if that makes sense). I've been lining everything up off the second and third mark. Is this correct?

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so i just talked to my service manager and it sounds like i am off a tooth, probably on the exhaust side. my cam marks need to be below the head line before i tighten the cam chain so that when i tighten the tensioner, they are level. i'm guessing thats my issue

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Jetting has absolutely nothing whatsoever to do with the issue of it not turning over.  There was probably no reason to change it that had to do with the exhaust or the '06 cam, either.

Since it turns over OK without the plug, it sounds like you have at least the exhaust cam advanced by one tooth or more. That will cause the auto decompression system to allow the exhaust valve to seat too early, giving you too much air to compress by means of the kick starter.  Double check your timing.

The '06 cam is entirely compatible withe the '08 engine, and makes a good modification for that year to broaden the power curve and beef up the low mid range.  Time it exactly as the manual calls for on either year model.

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Soooo after A LOT of head scratching, I finally figured out what the hell was going on..... That 06 cam I got was missing a timing mark on it! I was like 9 teeth off of where I needed to be lol. Got it put together and it fired up third kick... Taking her out this morning 

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Well went about 30 miles round trip today. Absolutely amazing weather and the bike was phenomenal. The 06 cam is a much different feel than the 08. Jetting was spot on as well. Ran in to snow and a ton of runoff and downed trees :)

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4 hours ago, grayracer513 said:

Lots more low/mid power ;)

yeah absolutely. I changed the rear sprocket last year as well (can't remember what I did.. 51 tooth maybe??) and that really helped bring 2nd and 3rd closer. overall way happy with it

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The great thing is that even the full '06 cam set doesn't really give up much on top to the as-built '08-'09.  But when you keep the later intake in with the '06 exhaust, it makes a really great combo that pulls a lot harder than the '08 at 4500-6000 and still screams at 8K+.

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