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Discussion Starter #1
I bought a 96 MXZ 670 about a month ago and when I checked the compression both cylinders had 165psi.
This last week-end I bought my son a 98 MXZ 670 and it has 145psi per cylinder. It had the top end rebuilt 250 miles ago and runs great. Why the difference? The 96 runs stronger and they are set up the same. Maybe the 96 has had the head shaved? I dunno......
Also both these sleds factory exhaust rattles are really annoying. Will it hurt to remove that alluminum cover on the pipe?
 

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dulie,

That compression seems high for the 670 (165psi), I would keep good fuel in it.  Also keep the heat sheild on.  Get some clamps from the hardware store and clamp it down.  There is also tabs on the side of the sheild that you can pean over to tighten the sheild up.

GLHRACING
 

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what is the stock compression for the 670?
I heard that gauge readouts can vary with different gauges. My mech told me that my compression is about 122 on both sides, I thought it was supposed to be 150, he said that some gauges read differently. He said my compression is stock and not to worry about it.
 

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Discussion Starter #4
I always run super unleaded (91 or 92 octane) in all my sleds.
I guess I`ll check the squish after the seasons over. It does'nt
have a spacer on the cylinder so if it`s been shaved I can do that to get the compression back down a bit.
 

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Either compression is good as long as they are within 10% of each other on the same machine. Anything less than 130psi I would start looking on a Rotax. Numerous reasons could cause the differances. One is getting more oil than the other, sealing the rings better. When one was rebuilt a thicher base gasket was used, raising the cyl, causing lower compression. Different porting. Other things can cause differences but as long as they are within 10% on the same machine you're good to rock.
 

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I had a 96 670, squish was at .050, compresion was 165. With the stock jetting and 93 octane gas, I wouldnt recommend holding it open for  even 2000` at 0'f.
 
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