Idle air screws

[csmadore]

Hello, everybody. New to the group.
I have a question about carb tuning.
I'm working on my 1973 K4, which ive been working on returning to the road after the previous owner parked it in his basement in 2007.
I have disassembled, cleaned and reassembled the carbs. I'm using OEM brass. I have bench synced using the 1/8" drill bit method (from airbox side), and set the air idle screws at a turn and a quarter. I'm going to vacuum sync next.
The question I have is: how/when will I know that my idle air screws need adjustment? Should I vacuum sync first? What are the symptoms i'm looking for if I need an idle air screw adjustment? Currently the motor runs decent but exhaust smells a bit gassy, if that makes sense. Any input is appreciated.
Thank you.

 

[Biebs]

Vacuum sync the carbs. Air idle should be at 1 1/4 as you stated. Adjust idle to 900-1000

Now throttle response off idle is the key. Is there a hesitation off idle to 1500- 2000 rpm.
Idle screws may need to be adjusted or idle adjustment.

The off idle hesitation is a switch from air mixture to slow jet. Idle speed also is in play.

Adjust to your taste.

Idle air screws should not be adjusted past 3 turn out just a guide line.

 

[csmadore]

Hello, everybody. New to the group.
I have a question about carb tuning.
I'm working on my 1973 K4, which ive been working on returning to the road after the previous owner parked it in his basement in 2007.
I have disassembled, cleaned and reassembled the carbs. I'm using OEM brass. I have bench synced using the 1/8" drill bit method (from airbox side), and set the air idle screws at a turn and a quarter. I'm going to vacuum sync next.
The question I have is: how/when will I know that my idle air screws need adjustment? Should I vacuum sync first? What are the symptoms i'm looking for if I need an idle air screw adjustment? Currently the motor runs decent but exhaust smells a bit gassy, if that makes sense. Any input is appreciated.
Thank you.

Vacuum sync the carbs. Air idle should be at 1 1/4 as you stated. Adjust idle to 900-1000

Now throttle response off idle is the key. Is there a hesitation off idle to 1500- 2000 rpm.
Idle screws may need to be adjusted or idle adjustment.

The off idle hesitation is a switch from air mixture to slow jet. Idle speed also is in play.

Adjust to your taste.

Idle air screws should not be adjusted past 3 turn out just a guide line.

Thank you so much!

 

[csmadore]

Ok. So I vacuum synched the carbs. Following advice I've gotten from several sources, I did the synch at a raised idle to ensure that the pull was consistent and strong at each carb (2000 rpm). This seemed to work well and I was able to get the carbs all within close range of each other. It idles pretty well now at about 1100. Any lower it seems to struggle.
But it does come off the idle pretty well without any hesitation. No stumbling or anything. A strong rev.
A couple issues.
-there is still a pop or two from one of the cylinders coming down off the throttle and at idle.
-i can still smell fuel quite strongly.
One last note: i have 4 into 2 exhaust (previous owner) and im quite sure the exhaust is modified. All the baffles are removed, or sound that way at least. Makes for an awesome sound, but is it perhaps affecting performance?

 

[Biebs]

Ride it for a bit. Do not over analyze. Do not attempt to fix if it not broken.

Seems like it is not broken. Might do a 1/4 turn out on air/ idle screws as a test after riding at least 20 miles.

Don’t over think.

 

[csmadore]

Ride it for a bit. Do not over analyze. Do not attempt to fix if it not broken.

Seems like it is not broken. Might do a 1/4 turn out on air/ idle screws as a test after riding at least 20 miles.

Don’t over think.

So scratch that last post. All my info came from running it on the center stand. I took it out on the road today, just around the block. First time the bike has seen the road since 2007!
But it didn't do that well. As soon as i let the clutch out and gave it some gas, it stumbled at about 2k. If I let off and eased it out VERY slowly, it came back. But I had a hard time chugging up the hill and not stalling. Eventually I made it around the neighborhood and back into my driveway, but I was never able to really give it the gas without it stumbling and nearly stalling. Since then I have adjusted the idle air screws out a full turn to see what happens, but all that seemed to change is that when I rev it up it stays high for too long. eventually it settles down but not easily.
Does this sound like a jetting issue? I am running original Keihin brass, and everything was (to the best of my ability) cleaned thoroughly. This wasn't my first carb rebuild or idle be tempted to think I screwed something up. My last (on my 75 cb550) went just fine and runs like a top.
But maybe I missed something?

 

[Loki]

Sounds as if it's running weak, did you try closing the choke to see if it ran better or not? What were your plugs like after your trip round the block?

Loki