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06' YZ250 detonation @ 1/4-1/3 throttle

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Bone stock except for a FMF turbine core II. Air screw is set to 1 1/8 turns, otherwise jetting is untouched from the factory. I ride primarily at 1000-1500ft, 70-80f, minor to no humidity and the bike flat rips. Throttle response is good, never fouled a plug and pulls like crazy on 91 octane and Amsoil Dominator @ 32:1.

I've noticed what I think is detonation just before the bike gets 'on the pipe' at 1/4 to 1/3 throttle. I've never had a 2-stroke that pings before so I'm not exactly positive thats what it is, but I'm failrly certain. I dont notice anything prior to 1/4 throttle or after 1/2 throttle and I'm unsure if its the pilot circuit, the main or the needle. I'd prefer to run pump gas, but not willing to burn a hole in my piston.

I know I've read past posts that this can be fixed via jetting, but my search skills blow and I cant find them. Any advice?

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It can be covered up with jetting but then its softing the power. The correct way to fix the bikes pinging problem is to get some octane in there.

The manual claims it needs 95 or higher.

I personally run a 40% race/60% pump mixture, with 110 sunoco race fuel and 93 pump. This is just enough to allow the engine to perform perfectly with no pinging.

I have tried everything from pure pump to pure race, at 40%/60% you get everything you would with 100% race.

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I may pick up a 5 gal can of 110 and see how that works. Will any jetting changes be required at 40/60 ratio? I currently mix Amsoil Dominator @ 32:1.

and whats the shelf life on 110? Can I get 20-30 gallons to sit on for a few months?

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Besides trying higher octane...........try staying a gear lower too. :thumbsup:

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I may pick up a 5 gal can of 110 and see how that works. Will any jetting changes be required at 40/60 ratio? I currently mix Amsoil Dominator @ 32:1.

and whats the shelf life on 110? Can I get 20-30 gallons to sit on for a few months?

Depends on your location, the jetting stock in my 06 down here in Florida seems to be spot on with the 40/60 mixture. In the dead of winter it can run slightly on the leaner side of the scale and after a rain in the middle of summer it can run slightly on the richer side of the scale. But never far enough to demand jetting changes unless you have nothing better to do. But otherwise its spot on year around. The air screw needed to be tuned out about a 1/4 of a turn though.

Easy way to figure out 40/60 is 2 gallons of race with 3 gallons of pump, that fills of a 5 gallon can and your ready to ride :thumbsup:

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