the manual you are referring to is talking about pressure testing not a compression test they are different a compression test checks the condition of the cylinder pressure testing is what you do to the entire motor to check if you have any air leaks, usually done after a complete rebuild

 

Thanks Rocky, it was confusing to me. VENOMOUS, are you doing the compression test with a gauge connected to the spark plug hole? Or are you doing a leak-down test? Rocky's absolutely correct, two completely different animals!

 

I was doing a compression test of the top end. The book states in chapter 3 not sure which page but towards the end, that Yamaha made no specifications of what optimal compression should be. It just says that each cylinder should be within 10% of each other. I didn't do a 2-stroke lower end pressure test yet and I'm probably not going to since I found my problem with the bent valve needle. The repair manual was the Clymer brand and it's not much good unless your a real shady shade tree mechanic. If I didn't know as much as I do about working on motors and such I sure wouldn't rely on that thing to help me. In the book it even has a little picture of a cheap little compression tester in the plug hole if anyone wants to look and see that there is no recomended compression for the Banshee by that book.

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Jeremiah Lucas

1989 Yamaha Banshee