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Old 04-30-2013, 09:02 AM   #4
disston
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Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 8,993
Increasing the jet sizes is what is noticed when the carb is used on a larger engine usually. Larger jets make for a richer gas mixture and these increases are incremental. The larger engine will need the extra gas but the carb set up for a large engine will be too rich on a smaller engine.

The jet needle is inside the needle jet and the needle jet can be increased. Those jets usually come in sizes thousands apart. I'm familiar with sizes 2.66 and 2.68. So an increase of the needle jet from 2.66 to 2.68 would be one jump in size. It is said that raising the needle one notch is a jump in 3 jet sizes.

These are not really hard fast rules about carbs and sizes. But the idea is that raising the needle is a bigger change than a jump in jet sizes.

You want to look at the spark plugs and see how rich/lean the carbs are running. This is tricky because the engine runs on different parts of the carb at different rpms. We do have idle jets and main jets and the needle jet/jet needle. They each work and have more influence at different rpms but they also work together.

I'm trying to not get myself in trouble here by writing a bunch of stuff that isn't really accepted. I don't mess with the jets in my carbs very often but I have tried a couple of things. I don't have the jet figures you want, in other words. I have heard of riders that got satisfaction from raising the jet needle. But I think I would have to lower something else on my bike if I did that.

Finally I will say that this was easier before we had to deal with Gasohol. It doesn't burn the same and it also doesn't leave the same color on the plugs, IMHO.

I would also suggest finding some legitimate Hot Rod or Racing forums and read what these guys do. And I bet you could find a bunch on just Carburetor Theory from a bunch of frustrated Physicists.
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disston screwed with this post 04-30-2013 at 09:07 AM
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