I did a compression test on the top end of my Banshee and the left cylinder read 92 PSI and the right cylinder read 90 PSI. I had a reply to a previous post that stated that the nominal pressure for Banshee's was 120-125 PSI's. When I did the test I followed the instructions in the Repair Manual made by clymer that said to leave the gauge on for 6 minutes. I left it on a little over 6 minutes and the pressure never dropped. It stated that if the pressure dropped a pound or more in one minute you deffinetly have a problem and if it dropped a pound in the 6 minutes the test lasted then it was probably OK. My question is that if my Banshee's top end is lacking 30-35 PSI's per cylinder then how can it hold 90 and 92 PSI's that it does have. I was thinking that if supposedly lacking pressure then how can it hold pressure. It should leak down pretty fast I would think or at least leak down some, but it does neither. I don't understand how this can be. I know in the book it states that there is no recomended pressure or written down pressure reading that applies to the top end of Banshee's. Any help is appreciated.

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Jeremiah Lucas

1989 Yamaha Banshee

 

Not really, it just means that the rings and the bore aren't close anymore. For a two-stroke to have less than 100 p.s.i. whether you wait 6 minutes or not isn't good. You'll need to have your cylinders measured, then order the next piston size (with matching rings) larger, have your cylinders bored and honed to the new piston size, make sure that you replace both your head gasket and base gaskets too.

 

does it run good? if so your probably not using the right tool to do the job but they say if your within 4 lbs from cylinder to cylinder your ok. my cylinders read 161

 

I would be interested in knowing what method you used to check your compression. I have been told to hold the throttle wide open and kick it about 20 times just a fast as you can.

I recently checked my compression and it seemed awful low. One of the engine builders here in town told me that my gauge may be inaccurate. I bought a Craftsmen gauge from Sears for about $25. He said that the gauge is pretty cheap. The ones he uses are much more accurate and cost between $150 - $250.

Hope this helps.

99" Banshee