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before rejetting, am i understanding all this right?

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i am wanting a confirmation on if I'm understanding all this correctly before i start on jetting today.

please add in anything i missed or anything i have backwards :ride:

for any reason the info is needed i am going to be rejetting with the JD jetting kit

main jet- bigger main jet will Enrich the mix

smaller main jet will make the mixture leaner.

pilot jet-bigger pilot will enrich

smaller will make the mix leaner

fuel screw ajustment- turning the fuel screw out will run the bike leaner

turning the screw in will run the bike richer?

needle and clip- *starting position on the needle will be the middle *which will be X # position from the top*

change clip position to the top or toward position #1 will make the mixture *leaner*

change clip position away from top or higher number clip position will enrich the mixture.

higher elevation makes the bike run richer

lower elevation make the bike run leaner

higher temp makes bike run richer

lower temp makes bike run leaner

high humidity the bike runs richer

when rejetting do the MJ first, clip and needle second, then pilot/ fuel screw third?

as far as rejetting i will be using this website as the guide to rejet my crf 250 04

http://www.thumperfaq.com/jetting.htm

for the MJ and needle im thinking i wont have to try different positions as i will just set it per JD instructions that came with the kit, im thinking i will just have to mess with the fuel screw and pilot

one thing i read is that the plug test is really not a good way to test the MJ. what is a really good way to test the MJ?

for the needle and clip this guide seems good to test it.

sorry for the long post, i hope i covered everything for the main jetting purposes. :thumbsup: correct me or any advice will be greatly appreciated, fyi i live in las vegas which is average 2k to 3k elevation with the two extremes of 0 to 30% humidity mostly with a temp of winder around 70-80* if remember right* to about 100-110 summer. any recemended settings i should note?

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Quite a post, indeed . . . you are thorough!

It appears you've got a good basic understanding of it.

The only thing I notice that is wrong is fuel screw adjustment:

Turning out will make it richer, not leaner. (Opposite for a 2 stroke 'cause it's an air screw as opposed to fuel screw.)

You also mentioned "when rejetting do the MJ first, clip and needle second, then pilot/ fuel screw third?" I'd say not necessarily. It depends on where (throttle position) you need the bike to run better. You may only have to change one or two items, or all of 'em.

Here's approximate throttle positions for the jetting circuits maximum effect:

fuel screw 0 - 1/8

pilot 0 - 1/4

clip/needle 1/8 - 5/8

main 1/2 - wide F'n open

Als, you can test the main via plug check; clean it out good, then run it wide open for a reasonable distance. Chop the throttle, hit kill switch, pull clutch in so motor stops turning. Now the plug should represent wide open conditions (which would not happen if you just cruised into the pits at partial throttle, then hit kill switch.)

What I like best though (for main jet) is to increase in even increments, taking note of how strong it's running. If it runs better WOT with next bigger main, you're going in right direction.

I'll increase main jet size until a very slight loss of power WOT, then back off a size or two. Good luck to ya!

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i am wanting a confirmation on if I'm understanding all this correctly before i start on jetting today.

please add in anything i missed or anything i have backwards :ride:

for any reason the info is needed i am going to be rejetting with the JD jetting kit

main jet- bigger main jet will Enrich the mix

smaller main jet will make the mixture leaner.

pilot jet-bigger pilot will enrich

smaller will make the mix leaner

fuel screw ajustment- turning the fuel screw out will run the bike leaner

turning the screw in will run the bike richer?

needle and clip- *starting position on the needle will be the middle *which will be X # position from the top*

change clip position to the top or toward position #1 will make the mixture *leaner*

change clip position away from top or higher number clip position will enrich the mixture.

higher elevation makes the bike run richer

lower elevation make the bike run leaner

higher temp makes bike run richer

lower temp makes bike run leaner

high humidity the bike runs richer

when rejetting do the MJ first, clip and needle second, then pilot/ fuel screw third?

as far as rejetting i will be using this website as the guide to rejet my crf 250 04

http://www.thumperfaq.com/jetting.htm

for the MJ and needle im thinking i wont have to try different positions as i will just set it per JD instructions that came with the kit, im thinking i will just have to mess with the fuel screw and pilot

one thing i read is that the plug test is really not a good way to test the MJ. what is a really good way to test the MJ?

for the needle and clip this guide seems good to test it.

sorry for the long post, i hope i covered everything for the main jetting purposes. :thumbsup: correct me or any advice will be greatly appreciated, fyi i live in las vegas which is average 2k to 3k elevation with the two extremes of 0 to 30% humidity mostly with a temp of winder around 70-80* if remember right* to about 100-110 summer. any recemended settings i should note?

fuel screw out is richer.in is leaner.

the sticky post at the top of the forum out lines how to confirm your pilot circuit.

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Als, you can test the main via plug check; clean it out good, then run it wide open for a reasonable distance. Chop the throttle, hit kill switch, pull clutch in so motor stops turning. Now the plug should represent wide open conditions (which would not happen if you just cruised into the pits at partial throttle, then hit kill switch.)

reading plugs doesnt work with modern unleaded pump fuel.

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sounds good guys thanks for replying i just wanted to make sure before i started,

i didnt want to be :ride: 'ing at my bike because i was doing something wrong :thumbsup:

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reading plugs doesnt work with modern unleaded pump fuel.

How come it doesn't work . . . do you mean it doesn't work with 4 strokes, or does that go for 2 strokes too?

Shoot, the manuals for my bikes mention plug reading as a way to determine conditions in the motor. Maybe they're assuming the operator runs special fuel or something?

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4 strokes.

a properly jetted 4 stroke will have a spark plug that looks like it just came out of the box.no color.

My YZ400F plug has the dark deposits on the outer part of the plug (at the end of the threaded area, outside of the electrode and porcelin) but the electrode and porcelin have good color, close to new-looking. What would this suggest regarding the jetting?

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OK, thanks for the tip. I'll have to re-engage this in a couple weeks; we're leaving for Colorado, dirt bikin' heaven.:-)

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