I have my fourwheeler jetted about 160 and it seems to run best around 60-70* now that it is up to about 85-90* it cuts out top end real bad.

So my question is:

Jet higher for lower temps, and lower for higher temps (right?)

and then if that theory is true, how far should i drop it. I was thinkin about down to a 148 or a 150. Thanks

 

Generally speaking you should go up on the main jet when the air temp. drops and down on the main when the air temp increases. Because the density of the air increases as the temp. drops you would need to go up on the main jet to avoid a lean condition and vice versa as the temp. increases. Also keep in mind to make small jumps when jetting to avoid hurting the motor (this is more critical on a 2-stroke)You may want to go down to a 158 then if that doesn't help try a 155 and so on. Good luck.

 

thanks alot !

 

Well, here is what happened.

I went out and checked the plug, It was pretty dark, almost black, but still had a good spark to it. That told me it was too rich. So i dropped it from a 146 (not a 160, i thought it was but is wasnt) down to a 140. that made it run 10x worse, so i did the next logical (or atleast in my mind) thing and went up to a 155 and it made it run about like it did with the 146. Then I tried a 152, about the same. What other thing should i be doing?

But i guess the thing that is bothering me most, is if i had it at a 146, and the plug was dark, when i went down with the jetting, it didnt get any better. Because its black, doesnt that mean it is too rich?

Also, is there another way to tell, like since its cutting out top end does that tell any of you expirienced people out there what the problem is? Thanks alot, looking forward to riding here in about an hour, or whenever i get fixed

Derek

 

got it fixed, it took a 142, cleaned the plug, and played with the air screw. Ohwell, thanks anyways

 

ahh, 85 - 90 degree weather. It must be nice

 

Derek- Where is the air screw? I was argueing with my dad today because he thought that my carb had an air screw, and I didn't think it had one. I guess my real question is does the 300EX carb have an air screw? I probably sound like and idiot, but I'm just tryin to pick up some information here to help me out with my jetting.

 

Umm, on mine, it was directly underneath. I think it is kind of a crappy design because you just about havta take the carb off to adjust it, makes it pretty hard when your trying to leave it running to figure out where the perfect setting is.