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Discussion Starter · #1 ·
Ok I need help. We burned a hole in the clutch side piston a few weeks ago. There was no scoring on the piston or cylinder just melted right through the top. I'm told this is from pre-detonation. We rebuilt the engine and the other piston was perfect. The same cylinder still seems to be running lean...the plug is a whitish/grey. I'm running it at 900ft / 20-30 degrees f. I have 310 jets in and the needle is in the center clip position. Gas is only 87 with oil mixed at 100:1. Plugs are BR9EYs. Plug seems fine at idle but hot if I check them after a midrange or top end run. The jet chart on the sled says I should be running a 270-300 jet so I shouldn't be running too lean and can't understand why it's only happening on the one side. Do I need to jet up, move the needle, change gas, change plugs or give up. Carbs have been cleaned several times so I don't think it's a plugged jet. Thanks.
 

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Discussion Starter · #4 ·
Sorry the sled is a 2001. I relplaced the gaskets all the gaskets between the intake plate and the block. The boot looks fine to me but not sure what I'm looking for. I can't tell you if the sled has ever lost a belt at a high RPM. The sled is a backup sled of my buddies and I was the lucky one who jumped on it and burned it down after 1 mile...hence I'm the one rebuilding it. I've been told that a lazy mans way to check for an air leak is to spray a little carb cleaner around the outside of the case seal and or intake seals and listen for an RPM change. Good idea/bad idea?
 
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