how do u check jetting properly?

[kilabeez0]

to check pilot and air/fuel screw do u just start it and let it idle and then check? and for main do u rev it all the way and then just cut the power and check?

[duke416ex]

I have always been told for main rev it out in about third and just hit the kil switch while wide open and take the plug out.

[wilkin250r]

Me personally, I think it's best to do it in fourth, but that requires a bit more open space.

Ideally, you want the engine under load, actually MOVING the quad. Also, you want to hold it in that condition for more than a few seconds. Let's say your idle is rich, but your main is a little lean. The rich jetting will have a black plug, your lean main should have a white plug.

You start your quad and let it warm up, and your rich idle will blacken the plug with deposits. If you're checking your main with a WOT chop, you need to give it enough time to heat up and burn those deposits off to SEE the lean reading. If you don't give it enough time, those deposits will still be on the plug, making you think that your jetting is good, or a little rich.

Likewise, if your main is rich, you need to give it enough time to coat the plug with deposits to SHOW you the rich jetting. This doesn't happen within a few seconds.

[kilabeez0]

ok so i do check the plug after just idling for a little bit to check for pilot and air/fuel screw?

[wilkin250r]

No, for two reasons. First, idle speeds don't really produce much heat, so your plug may not be getting hot enough to burn away deposits. I would be surprised if you could get lean enough to get a white plug and still have the bike idle.

Second, there is an easier way with idle.

Make sure your quad will idle, and then bump up the idle speed by adjusting the idle speed screw to about 1500rpm ( a very fast idle).

I don't know what model you're working with, so I don't know if you have a fuel screw or an air screw. Let's assume its a fuel screw. So you screw the fuel screw out, which richens your mixture, which will cause RPM to drop. Then, you screw it in slowly (get leaner), until you get to max idle RPM, then back off a quarter turn.

The theory is very simple, the proper mixture will result in the best idle, so you use the idle RPM to find the proper mixture. When you're done, reset idle RPM back to normal with the idle speed screw.

[kilabeez0]

so basically i get the idle up to 1500, unscrew the fuel screw to add fuel to drop the RPM's, and then turn it back in until I get the fastest possible idle? Why even bother turning it out to richen it? Why not just turn it in to lean it out and make it rev faster which is what i want?

~~and then back it out a 1/4 turn:cool:

[wilkin250r]

Well, yeah, of course. But I need to explain the whole procedure in full detail to make sure you understand the theory behind it. ;)