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Understanding Jetting!?!?

1482 Views 5 Replies 4 Participants Last post by  Rob B
I brought my foreman 500 06 model to the dealer to get jetted.

Everything sound good and it ran well my main jet was 170.

I went riding in the mud and it seemed, if and when i would get stuck in the mud and i would run at high RPMs WOT, after i let off the gas, it would come an idle and then kill. Also some times it would almost sound like it was back firing or miss firing. I went down to 160 main jet and now it sound good and runs good. The spark plug has that brown color where it was orignally white. It was all black at 170main jet. I don't understand, from what i discribed did i jet it correctly now? and why does some people have 170 main jet, are all engines different in there own way. I live south Louisiana, so you know i live below sea level. help somebody.

I looked at this site and my spark plug looks like the middle one !!
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Mine was doing the same thing this winter. I messed with A/F. I started at 2.5 turns out and ended up at 1.5 turns out. Now I can go from wide open to idle with now problems whatsoever. To much fuel.
Some people do run 170 mains but IMO I think its a little too much for the bike. I run a 165 on mine and I have the 499cc vs the 475cc. A 160 will work fine for you but you may get a little more with a 165 but it probably won't be that noticeable.
What jet size comes stock with the ES model? I noticed my plug was extremely black (rich ) when I pulled it out when I adjusted my valves and was wondering if I should adjust the A/F mixture or not. The thing runs fine as it is but I don't like it running rich if that's the case.

the stock jetting is 162 but the number differs from dyno jet numbers, they are not the same.

My spark plug looks good so i'm just going to leave it how it is. whats that saying if it aint broke dont fix it right?!?!?!
I'll probably lean it out a little with idle mixture then thrash on it and check the plug afterwards.
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