Carb a/f screw

[Andy.tech]

Quick question. I don't know when your introducing more air or fuel into the system. When you screw the a/f screw in till it can no longer go any further what is happening? Is that more fuel or is the air being restricted?

[mr72]

The idle (pilot) mixture screw is a needle going into the pilot jet. Tighter == less fuel at pilot. If you screw it all the way in, in theory, you should have no fuel at idle, barring leaks (which are likely).

[Andy.tech]

So as of now my spark plug is pretty black, does this mean I should screw it in to let in less fuel? I had it at 2 turns out

(Pilot is 42 main is 140 w/ K&N lunchbox and preformance exhaust)

[BockinBboy]

Plugs change - depending on what the bike was doing before it shut off last. Assuming it had been idling - then yes it seems as though you should turn it in... but I never hear of anyone turning them under 2 turns out.

If I recall correctly, most folks use 40 pilots on the 2 circuit carbs for lunchbox and aftermarket exhausts.  140 main sounds about right - but you'd have to plug chop to get a reading on the mains.

- Bboy


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[Andy.tech]

Yea it's weird cause I bought this kit from the Sigma team and I told them all the modifications i made to the bike and that I was at 5000 feet and they still sent those jets one was the 42 pilot (bike had a 37.5 jet)and then a 145 and a 150 (it came with a 118 main jet) which I was not able to use and had to purchase the 140 main jet and as you can tell it still running rich I set it to 1.5 turned yesterday and the plugs where kinda clearing up

[mr72]

If the plugs are black after riding (not idling) then it's too rich on main jet.

The 42.5 pilot is probably too big. Good to go back to a 40. 40 pilot and 2.5 turns out is pretty much right where you need to be.

You can probably get it ok with the 42.5 pilot jet. I wouldn't sweat it, just adjust in. But if you have to go with less than 1 turn out on the pilot screw, then you need to jet down.

[Andy.tech]

It's just a regular 42 but yes I was thinking that. The problem is that I'm in Guadalajara Mexico and I'm trying to ride back home to New York by the end of the month   

[mr72]

Just ride it then. A little rich won't hurt anything.

BTW mikuni jets come in 2.5 increments which is why it's hard to imagine a 42 or 118 jet. But I guess you got them from some other manufacturer. 42.5 and 117.5 would be more common. That would be an extremely lean main jet!

[Andy.tech]

Yes when I got the carb it had originally a 37.5 pilot and a 118 main jet. I don't know if the main was 118.5 cause it was so old that making out the numbers was not easy. As of now it has the Sigma Racing pilot jets I was sent of 42 and the smallest Main jet I could find here was 140. So that's what I'm running at the moment hopefully it'll get me to NY without fouling the plugs.

[mr72]

Yeah you'll be fine getting home. You are in the ballpark IMHO. If anything you may be slightly lean on main (with pods or lunchbox) and rich at pilot, which is not horrible. You can probably get close to where you want to be on pilot by adjusting the screws. I would just ride home with the 140 mains without trying to crack it open and shim the needle. Better to stick with what's already working than to risk breaking or damaging something during a repair when you are thousands of miles from home, IMHO.

[Andy.tech]

Awesome, so maybe before I go I'll switch out my plugs and get some new one just in case. Im also really hoping that being at the 5000 altitude is what is making it rich and getting to a more sea level altitude will help with the mixture.