What is the purpose? Small screw...

[dmobrien2001]

On my Keihin carbs, I notice a small, brass screw on the bottom of the carb, underneath near where it fits into the compliance fitting. I screwed one in slowly, counting the number of turns (3), and then backed it out the same amount.

What is the purpose of this small adjustment screw? How many turns should it have as a starting point for tuning? How to adjust it for best performance (running, starting, etc.)?

[QBall]

Sounds like your idle / air mixture. 3 turns seems like a lot. I think the average is 2 to 2-1/2. But if its aint broke - dont fix it

[dmobrien2001]

Sounds like your idle / air mixture. 3 turns seems like a lot. I think the average is 2 to 2-1/2. But if its aint broke - dont fix it

I started looking for things to fix as I have some popping on the left carb when cold even though I have the larger jet kit from Gene. This happens when the temp is less the 50F. It stops when warmed up, but the right one doesn't have any issues... So yes, it seems to be broke...

[BillyG]

That, my friend, is your handy dandy idle mixture screw. Should be at 1.5 turns out from GENTLY seated for factory setting (Keihin...not IMWA). Even if you have re-jetted, it should be somewhere in the neighborhood of 1.5 to 2 turns out depending on the temperature, altitude, humidity....After 2 turns you are really pi**ing in the wind as the carb will be running very rich.

If you cranked it all the way home tight...you could have squished/ripped the itty bitty O-ring seal that rides on the end of the needle, damaged the tip of the needle or even, if you were really ham fisted, busted/cracked the orifice in front of the Butterfly valve in which the idle needle tip juts up through...in which case the carb. will run extremely rich permanently.

But I don't think you are that lucky...hopefully.

[dmobrien2001]

That, my friend, is your handy dandy idle mixture screw. Should be at 1.5 turns out from GENTLY seated for factory setting (Keihin...not IMWA). Even if you have re-jetted, it should be somewhere in the neighborhood of 1.5 to 2 turns out depending on the temperature, altitude, humidity....After 2 turns you are really pi**ing in the wind as the carb will be running very rich.

If you cranked it all the way home tight...you could have squished/ripped the itty bitty O-ring seal that rides on the end of the needle, damaged the tip of the needle or even, if you were really ham fisted, busted/cracked the orifice in front of the Butterfly valve in which the idle needle tip juts up through...in which case the carb. will run extremely rich permanently.

But I don't think you are that lucky...hopefully.

Bill, read what I wrote. I screwed it in SLOWLY. I know not to bottom it out hard. Have a bad day or something? Sheesh.

So, mine is sitting at 3, it should be 1.5 - 2. I'll check the RH carb and then reset them both. Thanks for the info, I think.

[BillyG]

Nope, having a great day...for a change. Again...I guess if I don't put those stupid or icons after I pen something...some folks read what I scrawl with the wrong slant. But I have run into one or two folks who think I'm a peckerhead no matter what I do...not quite sure what column to put you under just yet (<----supposed to be a smile here).

No slight was meant or intended. Slowly don't mean gently...necessarily. I mean, Arnold Schwarzenegger and I probably have a difference in opinion as to what constitutes "heavy" when it comes to picking something up...so "slowly" could be up for interpretation in some circles. I was just listing the bad things that can happen "IF" (note I did start the sentence with "IF") one is not careful. And being you had no clue what it was you were turning, I thought it might be helpful for you to know what could be the end result...just in case the carb runs worse after twisting on the needle and you could not figure out why. But if you didn't eat your spinach or have your Wheaties when you tweaked the mix. screw...you're probably o.k.

[dmobrien2001]

I'll soon be 53 years old. I've worked on various carbs during my lifetime. I've learned enough that when working on an unknown adjustment screw on a carb to 1) count the turns as you screw it in, and 2) GENTLY (and slowly) turn it in, a half turn at a time.

Ya, I'm one of the two people whom you always seem to take a peckerhead stance with. Yes, it rankles me. I'll get over it. Thanks for your help.

ETA: I may be ignorant. But I'm not stupid.

[Spyder]

For what it's worth, and it's prolly not much, I don't see how BillyG's initial reply was anything other than helpful. I think it's more a matter of perception rather than intent.

That and some pocket change will get you a cup of coffee in most places

[dmobrien2001]

For what it's worth, and it's prolly not much, I don't see how BillyG's initial reply was anything other than helpful. I think it's more a matter of perception rather than intent.

That and some pocket change will get you a cup of coffee in most places

I know Bill and I go around and around. My simple queries seem to pi$$ him off. Guess I bring out the best in people.

He wrote:

If you cranked it all the way home tight...
...

But I don't think you are that lucky...hopefully.

suggesting quite directly that I fracked it up. I hadn't.

On another note, adjusted (CAREFULLY DAMMIT) to 1.5 turns out, my idle speed picked up a bit and it is much smoother. I'm going to have to take a quarter turn off each idle adjustment screw to bring it back down.

[Spyder]

I dunno, I figure if your questions pi$$ed him off he wouldn't answer them with such detail. I saw that last line as a bit of tongue-in-cheek humor that lacked a smiley for effect (something he cleared up in his follow-up post) and my take on your reply was that you jumped on him with both feet, but that plus the pocket change from the earlier cup of coffee will get you a cup of coffee in most places

I have an idea - let's all just ride our bikes and have fun

[Tin Man]

Ya'll keep on about these perceived slights and one of these days you are libel to ask a question and get ZERO responses. Wouldnt that be fun?

[dmobrien2001]

I dunno, I figure if your questions pi$$ed him off he wouldn't answer them with such detail. I saw that last line as a bit of tongue-in-cheek humor that lacked a smiley for effect (something he cleared up in his follow-up post) and my take on your reply was that you jumped on him with both feet, but that plus the pocket change from the earlier cup of coffee will get you a cup of coffee in most places

Ok, so I'm "sensitive". I'll go sit in the corner.

[dmobrien2001]

Ya'll keep on about these perceived slights and one of these days you are libel to ask a question and get ZERO responses. Wouldnt that be fun?

You're right. Bill doesn't need me, but I need Bill. Lopsided relationship, but true. I'll just ask my question and take whatever I get. Thanks for the advice.

[JohnBG]

"Can't we all get along?" --- Rodney King

[Barbosa]

I'll just ask my question and take whatever I get.

Sounds like me and my wife...*chucklin*