samo Posted November 1, 2009 Report Share Posted November 1, 2009 Hi! When lean I hear piston knock. Is it possibile when lean, piston hits the head?I hear just one or two knock when i turn the throttle of, or when i forget to open fuel. Is it possibile that when the main bearings are bad the piston can hits the head? I checked crankshaft and there is no play.. Greetings Samo Quote Link to comment Share on other sites More sharing options...
chewy Posted November 1, 2009 Report Share Posted November 1, 2009 yes when there is less fuel in the engine the conrod elongates and the main bearings get slack. Or it's possible that the leaner mixture of fuel detonates sooner than it might thus trying to send the engine into reverse rather than firing at just right moment and rolling over. If mains a shot you can hear a definite swishing/rolling sound nothing like knocking..best / easily determined with plug out and kickiing it over. Quote Link to comment Share on other sites More sharing options...
samo Posted November 1, 2009 Author Report Share Posted November 1, 2009 (edited) Thanks for reply Chewy.I already raised fuel level and air screw is only one and a half turns out. So I assume the mixture isn't lean and I stil hear this knock when I turn the throttle off. One main bearing has a little play, but not much. What should I do? Edited November 2, 2009 by samo Quote Link to comment Share on other sites More sharing options...
htrdoug Posted November 1, 2009 Report Share Posted November 1, 2009 Possibly weak ignition side crankseal drawing in air under high vacuum situation of throttling down. If that's the side that has a bit if main bearing play that makes it hard to seal up.(Seems I to love to blame crankseals for 2-stroke running issues!) Quote Link to comment Share on other sites More sharing options...
neil king Posted November 2, 2009 Report Share Posted November 2, 2009 No, your pistons not hitting the head. It is acting completely normal. Quit turning the gas off. Quote Link to comment Share on other sites More sharing options...
neil king Posted November 2, 2009 Report Share Posted November 2, 2009 And use better fuel. Quote Link to comment Share on other sites More sharing options...
chewy Posted November 2, 2009 Report Share Posted November 2, 2009 good thoughts from other replies.... dont forget with your carburettor you are adjusting an air screw not a mixture screw so it's in for richer out for weaker... float height is important also.....can you exacerbate the symptons by turning fuel off? remember most folk spend forever trying to get rev engines to carburate clean...adjustments may have been made!... personal opinion is that apart from carburretor angle .the exhaust isn't big enough on the rev series... feel difference by riding an evo Quote Link to comment Share on other sites More sharing options...
samo Posted November 2, 2009 Author Report Share Posted November 2, 2009 I use 98 oktan fuel. It is the best I can get here.. Yes Chewy with fuel off,or when I 'm riding a steep slope or when riding wheely knocking sound is oftener. Is there a solution to solve this problem? Thanks for replies guys ) Quote Link to comment Share on other sites More sharing options...
b40rt Posted November 2, 2009 Report Share Posted November 2, 2009 Halfords etc sell octane booster. Quote Link to comment Share on other sites More sharing options...
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