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I have an 07 TRX 450R that I got a couple weeks ago. It has ran excellent since I bought it, but died today and won't start. Doesn't seem to have compression all of the sudden. Instead of blowing out of the spark plug port when cranking, it wants to suck your finger in. The only things done to the bike by precious owner are exhaust, jetted and he changed to a higher cog for more top end. The geari g is almost too high for the clutch. I dunno if that coulda put a strain on anythibg or not. Any suggestions??
 

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Sucking in at the spark plug hole during the intake stroke is normal, but it should blow out during the compression stroke. If there does not seem to be a compression stroke, my first guess would be the cam is out of time.

This is easy to determine - just go through the valve adjustment procedure. You have to get the engine at TDC and you can check the cam timing then. If the cam timing is OK, check the valves and the auto-decompressor at the same time.
 

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Can be.....

Can be a few Things here.

1. Cam Some How Wen't out Of Time Some How.

2. Cam Chain Could Have Busted and cam is no longer even spinning.

3. Cam Tensioner is bad causing it to jump time.


Pull the valve cover off, pull the Spark Plug, Turn the engine over by hand you should see all 4 valves Stay Closed at "T Mark On The Flywheel" Or "Blow Your Finger Off The Hole If You Cover it With Your Finger" then when the Piston goes down the Exhaust Valves should start to open then when the Piston comes back Up The Exhaust Valves will close then the Intake should start to open Right after the Piston Starts to move down.
 
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