ModMMax
New member
Looking for advice re a noise I have never heard before. Engine is fresh 700 non power valve, ported, slp piped, head is Peak Performance c/w 19 cc domes. Set up is for 7500 feet and up. Worked great last season. Rebuild was this summer. Testing last spring at 1800 feet, before rebuild, used 50/50 C-12 and premium mix. Ran great, no detonation audible and normal plug color. Testing now at 1800 ft with fresh engine, same fuel mix, chop the throttle from full and there is a noise similar to a 4 stroke rap that occurs when you chop the throttle on an open pipe motorcycle. I know that an engine can detonate on deceleration but I have never heard it happen. Is this what I am hearing?
grapeape
New member
I personally was not able to hear my detonation problem. Nor did it show up on my egt's or water temp either. Bad gas was the likely culprit, as I had towed a Ski-doo 30 miles the day before without problems.
ModMMax
New member
Thanks grapeape. Today I'm going to increase the amount of c-12 in the fuel mix and see if that changes things. I think the fuel is already real slow. If I'm right, there is likely fuel in the pipes that is burning off when I shed throttle. Its really confusing. The noise sounds like it is coming from the left side of the sled. I removed the hood and belt guard so I could see if the transmission was acting strange but everything looks like it should. More as it happens.
ModMMax
New member
IT was fuel. Increased the C-12 and it stopped.