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2 stroke Detonation fix??

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Right now my YZ250 is having the detonation issues and I would like to know ways I can fix it .. wat are your suggestions? Someone told be just mix race fuel with it & its would fix it but I wanted to hear other people opinions

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-bad batch of fuel

-wrong heat range spark plug

-jetted too lean, fuel starvation problem (float/fuel level), air leak

-ignition timing advanced too much 

-physical damage to the piston's crown or cylinder head creating hot spots / pre-ignition.

 

also an important consideration, YZ250's often have the compression squish height set too large than optimal

(clearance between top of piston and cylinder head)

having that measured and corrected also makes for easier tuning (jetting) and a crisper running engine .

There are plenty of infos/discussions about this in the specific Yamaha 2-stroke sub-forum.

 

Blending in race fuel will stop it but it's just a band-aid fix.

Edited by mlatour
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What changed that you are now having detonation issues? 

No change new top end & fuel .. I believe I'm too lean on my mixture .. I mixed 93 with a 32:1

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Considering you didn't get a bad batch of gasoline,

if the jetting,  premix ratio etc. wasn't changed and detonation just suddenly started, you could perhaps suspect an air leak.

Don't take any chances and perform a crankcase leakdown test.

 

Also, pull off the pipe and have a peak at the piston crown's edge thru the exhaust port,

if you see any signs of erosion on the edge, refurb the top end before riding it again.

 

Edited by mlatour

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I have an '01 YZ250 and running 91 octane ethanol-free, I don't think I've ever heard a knock - even before I bumped the timing retarded a little to make it easier to start.  I'd also suspect a lean condition.  Do a crankcase pressure check..  Easy enough and won't cost much.  

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Same everything .. I did mess with the air screw a little so that might be my problem there

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