300EX Jetting

[MICHIGAN 300EX]

Hey im getting my motor machined out to a true 300 (.080" over) with 11:1 compression. I was wondering what size jets to run, my main is currently a 128 , i cant afford a cam right now so im gunna stick with the stocker.

Thanks

[bwamos]

Any headwork? New cam?

If no headwork, start with a 135. It will probably be a bit rich.. but it's better to be rich on breakin than lean. You'll probably end up with a 132 when your done. Stock needle and pilot should be fine. You'll probably need to move the needle up 1 spot (clip down), and adjust the air screw. You may not need to move the needle, or may need to go down. It's hard to say, you'll have a larger main wich affects the needle too.

I run between a 138 and 142 on my FST 330 below.

If you don't have a cam.. look at a stage2. It will compliment the 11:1 well. Can be added in later of course.

[MICHIGAN 300EX]

Also what octane gas should i run in it?

[JOEX]

Originally posted by Chicksdigme423
you are stupid
If you don't have anything positive to contribute then leave:grr:

[bwamos]

With 11:1 on a 300ex you can run premium pump just fine. (91 octane around here).

[rooster300ex]

I wonder why at powroll it says compression ratios 11:1 and higher require race gas.

[bwamos]

In response to the above poster.

Sometimes on a really hot day, 100+ deg out in the dunes, you either have to richen it up a little (to cool it off) or mix about 25% race fuel or you will get some detonation under heavy loads due to it being extra hot.

But, normally you'll have no issues.

Mainly they say that, because the 11:1 is right on the borderline for an air cooled engine. Anything higher will require at least a mixture of race fuel.

It's more of a CYA clause. If you are running a little lean it will detonate on 90deg days and can damage your engine. Most people run way too rich anyway.

If you run 11:1, I would definatly toss on an Oil Cooler. It will help a lot.