Jetting question for 4-wheeler

I am working on my bro's 89' Yamaha warrior quad. It had a horrible bog... so I to the snorkle off, raised the needle 2 positions, and tinkered with the air screw.

I have 2 questions...

1) On the warrior, does it have an "air" screw, or a "fuel" screw. In other words, does turning it in make it leaner, out = richer... or the opposite?

2) I have read on here that different parts of the plug read different colors, and thus indicate jetting changes needed. I did a jetting run, wide open in first, pulled clutch, and killed it. The very top of the plug was a dry black, the insides of the plug were a little bit lighter black, and the tip of the plug (im always confused about jetting lingo, but i think its called the electrode... its the metal part that the spark jumps from) was white.

What does this mean?

Im not too worried about the blackness... it never fouls plugs and has good power. Its the white (electrode?) that im worried about. I know it wont seize or anything since the main jet is plenty big enough, but I still hate to see white on a plug. Any help is appreciated! :)


I think the screw is an air screw

Heres a site that might have some answers


I wouldn't worry about it too much because the warrior is a 4-stroke and it's a lot harder to lean-seize a 4-stroke than a 2-stroke. Remember, the only way a 2-stroke gets oil is through the gas-air mixture, if you go to too much air the bike is deprived of the cooling effects of gas and especially oil.

The 4-strokes will tell you they are too lean in other less harmful ways.

Good luck, that 350 4-stroke is pretty bullet proof so don't worry too much, just ride it.

Thanks for the site UncleRich... I found it is an air screw.

Im not too worried about it seizing, I was just trying to tune it a little better for my brother for better throttle response. When he first got it, there was a gasket missing from the carb, letting all the air in that wanted in... it still didnt seize. The plug was white and had been ridden hard for a couple rides, still no damage, lol.

It's one tough motor. Thanks for the help and advice :)

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