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High Compression Piston and affects

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Guys,

I just put an '08 piston in my son's '07 250F. I was curious of others that have gone to a high compression piston needed to rejet. His bike was popping a bit. Opening the fuel screw to about 2 turns seemed to clear it up. The pipe was sealed well with high temp RTV at the joint and a good gasket at the head.

The fresh hi comp piston made good power during my quick test on the street. We took it to the track to break it in and give it a thrashing. Regrettably he didn't get more than about 2 easy laps out of it at Perris. The starter shaft broke, allowing the starter gear to engage and bring the engine to a stop.:) That little shaft will set you back $120.

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It changed my jetting a little on the FS circuit. It really made a noticeable diff in the needle forcing me to change needles. The 07 needle is wrong! Try an 08 or a JD. I went with the JD and have liked the results.

I've noticed HC pistons make good jetting run better and bad jetting run worse (or at least more noticeable).

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It changed my jetting a little on the FS circuit. It really made a noticeable diff in the needle forcing me to change needles. The 07 needle is wrong! Try an 08 or a JD. I went with the JD and have liked the results.

I've noticed HC pistons make good jetting run better and bad jetting run worse (or at least more noticeable).

Thanks for the feedback.

I read a couple posts about the '07 and earlier needles. I'll give the '08 a try. They are cheap enough.

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