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Discussion Starter #1
This week I replaced the OEM piston with a Wiseco. I kept the stock reeds.

I bought a compression tool, and measured the compression. After six kicks, i reached maximum compression that I could reach, which was 222 psi.

The service manual says my bike has a usable range of 119 ~ 185 psi.

One thing that my knucklehead-self did not do is open the throttle all the way during each kick. Common sense tells me that opening the throttle may make a difference somehow. I figure opening the carb and allowing fresh air in might stir things up a bit in the cylinder, but I dunno.

I bought the compression tool after I replaced the piston, which is ***-backwards...I know. I am the original owner of the bike and this is the first time any work has been done to the top end & piston.

What are your comments on my facts and findings?
 

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Another old dirt bike guy
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566 Posts
Did you happen to use a Moose gasket set? If so, they make a high compression base gasket kit, maybe that is what you got mistakenly, this would explain higher than normal compression.

Or maybe the compression tester is off?

Normally I have to give a bike 15 - 20 kicks to reach maximum compression.

Have you already broken in the new top end? If not, it will only get higher as it breaks in, more than likely anyway.
 

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Real Men Ride Rockets
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I kick mine about 10-12 times with the throttle wide open to get my reading. I always use oem gaskets and never had an issue with them.
 

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Discussion Starter #5
I used OEM gaskets purchased from my Kawasaki dealer.

I'll retest again this weekend, with throttle open.

Should i turn the gas off?
 

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Another old dirt bike guy
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Throttle needs to be open so that you get a good cylinder fill, this will make the reading higher if anything. You do not need the gas to be turned on.
Maybe this is just the calibration of your tester, try another tester or go buy another one for like $20 at the auto parts store if you can't borrow one from a buddy or friend.
If you didn't have the cylinder gasket surfaces milled, the head milled, and are using OEM gaskets then there is no reason it should be above factory specs. That is unless someone had the head milled to raise compression before you bought the bike, which I doubt since you said you know the previous owner and he hadn't touched the top end. All of this makes me question the compression testers acuracy. After all, most defects cause low compression not high compression. A little extra compression will actually give you more low end torque, some guys mod an engine for this very reason.
 

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Discussion Starter #7
i am the original owner of the bike. i bought it off the showroom floor 2 years ago.
this is a good tester, i believe. here it is:

Motion Pro Compression Tester [W/ 23-5407 - M/ 55-407] - $96.76 : A&D, Discount Performance

it's brand new and this is the first time i've used it.

For now i am not concerned. I will get the bike out tomorrow and just ride it. I am confident that all the mechanical work done on the cylinder, piston and gaskets was flawless. So do the two guys who helped me do it.

so for now i'll shut up and ride! will keep you guys posted......
 

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Why is my compression reading high?

There is another reason why your compression reading would be high without: having the head milled and using gaskets that raise the static compression ratio of the motor. When you run any motor, overtime carbon will build up on the head therefore causing a raise in the compression ratio.
So if you "decarbonized" the head and aren't using a milled head and lower thickness gaskets then you might have: a compression tester that's not accurate or you're just one lucky ******* that has perfect ring-to-bore seal giving you absolutely no blowby.
Now, go and clean your head. lol:-D
 

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Good info SBC but check the dates, otherwise you make yourself look a total jock strap.
 
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