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Test run on the new tune on my CR250R

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Can you give us any specifics on what porting and head work you did??

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I changed the angle of the squish. It's got a flat squish on the outside with 0.020" clearance, then a small transition angle into the combustion chamber. Spark plug has been indexed so that it is flush in the combustion chamber. It's running great on 106 octane fuel.

The cylinder:

Previous owner had done (or had someone do) the typical DIY porting where they hog out the transfers where it's easy to reach, and knife edge the boyeson ports. None of the timing had been changed. The bike was soggier off the bottom than it should be, even granting that it is a '97 cylinder that was known to be a little soft on the bottom. I believed that the increased volume in the transfer passages was affecting low end charging, so I used JBweld and filled the transfer passages back up. The volume in the transfer passages is less now than it would have been stock. It was ridiculously easy to do, and can easily be changed back if it doesn't work out.

I then widened the transfer openings, but didn't change the timing. The total effect should be that there is less total volume, and thus higher velocity into the cylinder at lower engine speeds. The previously stock port windows bottle necked the huge transfer passages, so opening them up should (I hoped) let the engine breathe better at high rpm, even with the tighter transfer passages.

I opened up the exhaust boost ports in the cylinder and also in the exhaust valve itself, all the way out to the main exhaust port. Didn't change the timing on this, but it will definitely let more gas pass.

On the main exhaust port, I noticed that my exhaust valve at full open was 1mm higher than the cylinder wall. So I raised the port to be flush with the exhaust valve at full open, and slightly widened the total port window. This was the only change in timing on the bike. The cool thing about this is that it doesn't change the exhaust timing when the exhaust valve is closed, so there is no loss in low end.

Other than that the bike has VF3, the stock Keihin PJ, and an FMF fatty. The piston is a new ProX, and I'm running 4.6* oxygenated fuel.

It honestly shocked me the first time I rode it with the jetting sorted out--and I'm no stranger to modded 2-stroke engines. The bottom end is much improved, so I think the JB weld in the transfers has been a good thing. But the overrev now is killer. I rode the bike last weekend at our local track, and found myself riding in higher gears everywhere on the track because the bike pulls down low so much better. But then in the higher gears, it revs out so frikin' hard that I was scaring myself at the end of straights. I'm sure I've gained 1000 rpm on the bike, and it pulls hard the whole time. I am now second guessing myself for going with a ProX cast piston.

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