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Discussion Starter #1
Hi

I have a friend's raptor 350 that smokes when is cold, once it warms it doesn't.

Does anyone knows what it should be the stock cylinder pressure?

He's done a pressure test and he's got 71psi.

Thanks
 

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and it's actually running with 71psi? holy shit...
 

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:wow:I can't believe it was running either. I don't know on 4 strokes but on my shee at about 95psi It would take alot of kicking to get it started so sounds like and bore and new piston and rings would be helpful. I would check your valves and make sure there adjusted right though. I'm no expert and hope QM or willy comment though. They seem to know about everything and should be able to help...
 

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Master of the Electron
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I doubt it was a valid test... probably should do it again - the bike likely would not run with that low compression.

Smoking after sitting cold, but going away as it warms up is usually indicative of leaking valve stem seals - nothing to worry about unless the smoke becomes continuous.

And thanks for the compliment.

If it IS that low, first thing I'd check is valve adjustment - make sure they haven't worn tight, keeping open a bit when cold... as the engine warms up, the aluminum head expands faster than the steel valve stems, so the rockers get pushed away from the stems, opening the clearance up enough to make it start and run well, once it's warmed up - but a BEAR to start cold due to compression loss.
 

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Discussion Starter #5
Thanks for the info ;)

I'm sure he did a wrong test coz he didn't know he must warm the engine before and do the test with full open throttle..

I translate all the info I see here to a Spanish forum where he asked for help.

I'm waiting now for his second test and, I hope, he does it right now.

Cheers.
 

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let me know if i'm wrong but, i don't think you are supposed to test the compression with the throttle wide open..
It shouldn't matter what rpm the engine is at when testing, it's always putting out the same amount of pressure in the cylinder. Doesn't matter if the engine is at 9,000rpm wide open throttle, or 1,500 rpm idle, the psi should always be the same and 71 is way too low of a number for an engine to run.. what does the raptor 350 normally put out about 120psi?
 

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Discussion Starter #7
let me know if i'm wrong but, i don't think you are supposed to test the compression with the throttle wide open..
It shouldn't matter what rpm the engine is at when testing, it's always putting out the same amount of pressure in the cylinder. Doesn't matter if the engine is at 9,000rpm wide open throttle, or 1,500 rpm idle, the psi should always be the same and 71 is way too low of a number for an engine to run.. what does the raptor 350 normally put out about 120psi?
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Well.. Raptor 700 service manual says I need to warm the engine before and then, With the throttle wide open, crank the engine until the reading on the compression gauge stabilizes, but it doesn't explain why.
I just guessed this procedure would be the same for the 350 but I may be wrong.
 
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