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Discussion Starter · #1 ·
I just got done cc-ing my 727 and I've come up with 11.74:1 as the compression ratio(which sounds spot on since the CP piston is rated at 12:1 and my combustion chamber is actually larger than stock because Kenz modified it to unshroud the 1mm oversize valves). So here's the question. What's the limit of 91 octane pump gas? I'm actually planning on running 3 base gaskets(to help out my close piston to valve clearance) this time around. So my compression should end up being right at 11.0 to 11.25:1 when all is said and done. Anyone think that's still too high for 91 octane?
 

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I think you should be fine. Why is your piston to valve clearance so close? And if you dont mind saying which camshaft?I assume that either or both your head and/or cylinder have been milled?
 

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Discussion Starter · #3 ·
scholle said:
I think you should be fine. Why is your piston to valve clearance so close? And if you dont mind saying which camshaft?I assume that either or both your head and/or cylinder have been milled?
It's a Megacycle X4. I know both have been milled at least once. Come to find out, it already had two base gaskets on it. Now it's gonna have four. :crazy:
 

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AZ, I just finished a 760 today that has obviously had a 105 sleeve installed and the cylinder decked, it has 1 base gasket, .040 squish height and .090 exhaust valve to piston clearance, .150 intake to piston clearance with an x4 cam and 12:1 CP piston. If you have to use more than one base gasket I'd recommend you order a base gasket to fit a Yamaha XT600E, it is a double base gasket that is rivited together, that way you don't have to worry about them seperating and leaking.

If your cylinder and head have been decked enough to cause these kinds of interferance problems, you should degree in your cam to make sure the cam timing is correct.
 

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Discussion Starter · #5 ·
CoalShedRacing said:
AZ, I just finished a 760 today that has obviously had a 105 sleeve installed and the cylinder decked, it has 1 base gasket, .040 squish height and .090 exhaust valve to piston clearance, .150 intake to piston clearance with an x4 cam and 12:1 CP piston. If you have to use more than one base gasket I'd recommend you order a base gasket to fit a Yamaha XT600E, it is a double base gasket that is rivited together, that way you don't have to worry about them seperating and leaking.

If your cylinder and head have been decked enough to cause these kinds of interferance problems, you should degree in your cam to make sure the cam timing is correct.
Too late, it's already together and running. I used metal base gaskets and some GM assembly adhesive in between them. We'll see on the leaks. As for the cam timing, I set it just like it was when it dynoed at 67 RWHP on stock carbs, one tooth retarded. The valve clearance issue was with the center intake valve. It must have been just barely touching, as it wasn't bent, but left a light impression on the CP piston. I'm guessing I probably floated the valves a few times and that's when it was touching. :crazy:
 

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Discussion Starter · #7 ·
CoalShedRacing said:
ok then, sounds like everything is fine now.
Any opinion on whether or not it'll run okay on 91 octane?
 

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i think you should be fine with that
 

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if you can i would also try to mix it to make it a little higher just in case
 
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