15 YZ250FX rebuild, no start

McG194
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Palm Coast, FL US
My bike had a leaking head gasket so having to fix that I might as well put a Cylinder Works 270 kit in it right?

Trouble is I have put it back together following my manual and it isn't starting. I just put it back together and left the same shims in and didn't bother checking them so I was wondering if that could be the issue so I pulled the valve cover off and checked and all were in spec. The one thing that concerned me is when I reinstalled the cams I set the dots even with the head but when I installed the chain tensioner the exhaust dot would rotate like half a tooth below the head. With that being said that shouldn't be off time enough to not start at all or at least backfire. I checked the plug and it is firing properly and I have good compression and gas. I hook up my tuner and it is not showing any codes. To me it seems that it has to be timing related like 180 degrees off but I just don't see how that's possible.

Anything common to these bikes that I'm missing or suggestions on what road to take to figure this out.
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Paw Paw 271
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Benton, LA US
2/9/2020 8:57am
I hate to tell you, but yes that little bit of an issue with the cam timing dots will keep it from starting.
Did you replace the cam chain during the rebuild? If not you need to do so as it has exceeded it's wear limits.

Paw Paw
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McG194
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Palm Coast, FL US
2/9/2020 9:25am
That sounds logical and it was something that was gnawing at me as being a potential problem but the engine has a bit under 65 hours on it. Seems crazy fast for a timing chain to wear out, the manual doesn't even have a recommended service interval.
garagedog
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Tulare, CA US
Fantasy
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2/10/2020 8:29am
Got to be exactly on TDC when putting the chain on. Try again.
McG194
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Palm Coast, FL US
2/11/2020 9:36am
Guess who is a complete idiot?

That's right it's me.

I tend to be a fatalist and look for the worst possible problem instead of the easiest. Trying to restart the bike the battery died in short order. I didn't have a lithium charger for my Anti-Gravity battery so I ordered one and last night I went out there and before tearing down again I shot some starting fluid directly in the spark pug hole and it fired right away. Next step was to put the fuel tank back on and connect it and it fired up and ran with no issues. I have had street bikes that would turn over but not have enough juice to power the ECM enough to run and that must have been my problem. It started easy enough that my assumption is that if I took it off the kickstand I could have kicked it to life pretty easy.

I knew there was no chance the cam chain was bad enough to cause a no start after 65 hours. From installing the cams to installing the tensioner it retarded the exhaust cam maybe 3 degrees if that much. I was just being paranoid and fatalistic as I said. Talked to a Yamaha tech this morning and he agreed that it was totally normal.

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