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Bigger or Smaller Main Jet

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Hi,

I got my engine bored from 250 to 290 and took my compression from 9:1 to 10:1. I have the idle circuit fine, it accelerates nice from 1-4K and has power from 5K-10K. From 4K to 5K it stutters once the engine gets hot and will lurch. If I accelerate hard when the engine is hot, it will pop and start to bog. I can ride, pop the throttle open all the way and it will shut off the engine if I kept holding it that way.

Before the big bore kit, I was running a 30 pilot and 165 main. clip in the middle and it ran great all the way. Right now I have a 35 pilot and it idles great but I am still running a 165 main. I was told to drop down the main but I'm not sure how far I should go. I don't want to go buy up a bunch of jets if I can get a rough estimate of how far to go. Would dropping to a 160 be enough or should I go down all the way to a 155? I figured I bored it 15% over its normal displacement so it should be a healthy jump down.

Please let me know how far you think I should drop.

Thanks

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1972 Honda XL250 with Mikuni 32mm and Pod Filter

I messed with the clip in every position. I noticed that it got better once I went more lean. I originally was running a 200 after the bore and it was way worse. As I dropped closer to 165 (my lowest size I have), the rpm span that it would lurch went down. When i had the 200 in, it would lurch from 4K-5500K, at 170 it was from 4K-5K, and now its around 4500K-5K. I could be wrong though.

Just as a note, my ignition is fine, the points, coil, and condenser are all new.

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