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If I run this engine at 65mph in 5th gear about 3500rpm. It's purring like a kitten. When I get to 70mph+ and 4000+ that is when the noise come in. If I "maintain" 4000rpm, but ever so slightly let off the throttle, it's back to being a kitten. Touch the gas to hold speed and back to noise. The noise will also clear up when going slightly down hill. Up hill or a headwind makes it worse.Wrist pins and bushings are perfect.It has been mentioned it could be a cam issue. Maybe out of time. I triple checked that the marks were line up on the sprokets. This is twice I've dealt with the sprokets. First install and when I changed to Valtec style tensioner.Two stroke oil?? Hum.... I do have some of that. Would I mix it like for my outboard? 1/2quart per 6 gallons??Thank you,Tom
I have renamed the thread to include why I was thinking of the octane booster. I would like to keep this to timing and fueling.If this engine didn't run so well and quiet below 4000rpm, I would say I had a rod issue or the like. I really feel it's ignition or fuel.I had mentioned that I can make the noise change with timing. Less timing quieter, more timing more noise and earlier in the revs.While timing the bike in the garage, I over advanced the dist. to about 15-20deg. Idle was up and seemed to idle smoother. I kept that info in my mind.If you were to time a '60's V8 for instance and didn't have a light, you would adjust the dist. to get it to start. Then you would turn it until you had the highest idle. When you put a light to it, you would be very close to where it should be.On a test ride down a freeway that I to test on. I pulled off where I turn around to head home. Decided to adjust the dist. by ear like a V8. Engine started up fine. There is a hill right there, starting up on the short hill it was noisy, like I didn't know how to use a clutch. Got to flat ground and another start, not too bad. Got on the freeway and what a racket!!!! At the next exit I pulled off and getting to a parking lot to work on it was a very noisy experience. Put timing back to about normal and headed home.I would love to put my ear next to the engine to hear where it's coming from. I don't think I can run fast enough to do it at 70mph
The purpose of octane booster or higher octane is to slow the burning rate of fuel on the ignition stroke through the first 45 degrees of the power stroke. This produces more energy for a longer period of time. Adding mineral spirits to your fuel would slow the combustion process. Or some two cycle oil.