air fuel mixture screw?

[DirtDiggler]

I ran my 400ex this weekend with a gps to see what I got for a top speed just for laughs. My buddy Doug hit 67.7mph with a stock 400ex. I ran it and only hit 64mph.

Today I brought my main down from a 155 to a 150 and it hit 68.4 mph. The idle seamed low and I had adjusted it up a while ago so I wasn't sure that the idle screw had moved or something else was wrong. I tried turning the air/fuel screw both in and out and it seemed to do nothing to the idle or when I road it.

I was wondering what the stock setting is for this screw and where it should be considering my mods which only consist of a White Bros E-Series slip on, Uni filter and outer wear and the rejet of 150 main 40 pilot with the needle clip set one notch richer.

I changed the plug and it was brown where it fires and closer to black around the sides. I put the new plug in but I haven't checked it yet since I ran out of time.

Thanks in advance for any advice.

[DeCap27]

lol sounds like u dont know what ur doing and BURT your rings...
U feel any power loss alittle?
Well u might not notice it anyway untill u fix your rings anyway..

[DirtDiggler]

I didn't BURT my rings it was just running a little rich on the top end. It didn't stumble or back fire or anything and it runs fine right now. It pulls harder than stock and I picked up a little top end I just want to know how to set this screw properly.

[DeCap27]

Originally posted by DirtDiggler
I didn't BURT my rings it was just running a little rich on the top end. It didn't stumble or back fire or anything and it runs fine right now. It pulls harder than stock and I picked up a little top end I just want to know how to set this screw properly.


i wouldnt even mess with it unless u know what ur doing.OTher then that take it to a shop and have them ajust it..

[DirtDiggler]

I did a search on it and found out the stock setting is 2 and 1/4 turns from just barely seated. I went up to a 40 pilot and I'm going to set it back to stock and turn it out and see if the idle goes up or the bike runs better. If not I'll run it at stock but I think it'll probably be some where between 2 1/2 and 3 turns out when I'm done.

BTW,
You can pay a shop mechanic $60/hour to adjust your air fuel mixture screw I'll pass. It's not that big of an adjustment. All though if you think it'll burn your rings maybe you should stick with the expense of a mechanic.

There are some very knowledgeable people on here who have given me excellent spot on advice. I take it when I can to save a buck if I know it's something I can't handle then I'll pay a mechanic but for jetting or other simpler things I'll do it myself.

[F-16Guy]

This is how I adjust my airscrew:
Set airscrew about 2 3/4 out. Start the engine and go for a warm-up ride. While running, set the idle as close to specs at possible (if you don't have a tach, use best judgement). Slowly turn airscrew in (lean) until idle starts to drop, then slowly turn airscrew out (rich). Stop when highest idle is attained, and then lean out 1/16th-1/8 of a turn. Reset idle speed. This should get you very close.

[DirtDiggler]

Thanx man I appreciate it.