Duel carb idle adjustment

[tom'sB2B]

I've been working on adjusting the idle. It's just not quite where I want it. It's still a little rough. I am wondering if anyone has come up with a good procedure to adjust duel carbs. I am using the tool in the picture below to sync the two carbs. Any suggestions will be appreciated.

[Ajgkirkwood]

Areyou playing with just idle screws? If so tighten both up till both are closed (lightly snug, dont tighten them right down) then back off 1 and a half turns as even as possible. What is your fuel pressure set at? I had to be at 2psi. I'm on 3 carbs but dont thi k that matters too much. 1.5 gave me issues

[Ajgkirkwood]

Both jets and float bowl height the same? No vacuum leaks?

Edited April 15, 2019 by Ajgkirkwood

[tom'sB2B]

Both carbs were built by George Asche and mounted to his aluminum intake. I put them on out of the box. I've been trying to adjust the speed and mixture screws with one carb and then trying to match with the other. I will have to search for vacuum leaks. If all else fails, I guess I will check float bowl hights and jets. I'm running a mechanical fuel pump. Just thought that maybe someone has an adjustment procedure that I'm not doing.

 

 

[9 foot box]

   I've disconnected the linkage to one carb and set the idle to both carb's and then adjust the linkage I disconnected, to slip back on. 

[greg g]

You need to set the idle speed speed to as cllose to 500 rpm. Then using the synching to to assure that bother carbs are dreaming equal voulumn and that when you advance the throttle they draw the same though the rpm range. This is acomplished through adjusting the individual linages to put the throttle plates at equal angles.  This can be a verry fiddly process caillng for methodic and patience. Once the throttle plates are synched you can then adjust the idle air screws to smother out that balance then reset the idle speed  for 450 to 500 rpm. When that if finished recheck your timing and check the volume with the synch tool again.  Once they are set you shouldn't need to mess with them gin unless the linkage loosens up over time and use.

[greg g]

wow just re read the above.  must be high on flu meds.....  can you understand or should I repost an edit?

[RNR1957NYer]

Flu meds, or...

 

.....you shouldn't need to mess with the(m) gin...?

 

actually helpful, though.  

[Don Coatney]

1 hour ago, greg g said:

wow just re read the above.  must be high on flu meds.....  can you understand or should I repost an edit?

 

 

Edit and correct.

[oldasdirt]

21 hours ago, tom'sB2B said:

I've been working on adjusting the idle. It's just not quite where I want it. It's still a little rough. I am wondering if anyone has come up with a good procedure to adjust duel carbs. I am using the tool in the picture below to sync the two carbs. Any suggestions will be appreciated.

Beautiful setup. I see you have one of the new AoK dual carb intakes.    There are some great suggestions on the thread  and the issue I see may not be the whole problem

although from experience with dual carbs I know it can provide you the exact issue you had.    Your running a fuel line to the 1st carb and t-ing right at the main jet to the other

carb.   That gives you an fuel pressure balance issue.   The correct way to plumb it is to go from the mechanical fuel pump to a fuel block, and then run lines from the fuel block to each carb.

[Dodgeb4ya]

All my Dodge truck dual carb factory fuels lines are done like this.....

[Don Coatney]

This is how I ran my fuel lines. I had no issues adjusting the carburetors.

 

 

I had a fuel block but I elected to not use it.

 

[oldasdirt]

3 hours ago, Don Coatney said:

This is how I ran my fuel lines. I had no issues adjusting the carburetors.

 

 

I had a fuel block but I elected to not use it.

 

Thanks for your illustration Don, showing my point quite well. You are,  or were running a few block.albeit fairly close to the carb.  In Toms case he has the  point he is diverting fuel right up to the main jet.   When I have done that years ago I got into the exact issues he is reporting.   I have no idea in your case how similar your situation is.  Something made me think

I read you playing with electric fuel pump and  lots of carb adjustments.   In the end it matters not

 

My point was I have found the further away from the connection to the carb you split the better. 

[oldasdirt]

11 hours ago, Dodgeb4ya said:

All my Dodge truck dual carb factory fuels lines are done like this.....

Interesting..  That looks like a 331, 377 or 413 series engine.  I have no experience with those so would have to concede to your experience.    I know about 40 years ago

when I was having issue with my 1st dual carb setup I  ran into Eddy Kingsbury and saw a 265 with a factory dual carb setup on it and the  fuel block had pretty close to

equal length lines to each carbs.  It was after that I went home,  changed mine to a fuel block that I mounted on the fire wall and lines from there to the carbs.

That was the only change I made and it went from running rough to running smooth.  Since then I have done several multiple carb setups and done similar fuel block setups.

 

That is not to suggest you need to go to the firewall. I can see good reason if your running metal lines not to go to the firewall.   

 

Now what I do see if the fuel block your running is prior to fuel bowls and the main jet.  I wonder if that  has an effect ?

 

[Don Coatney]

14 minutes ago, oldasdirt said:

 

I read you playing with electric fuel pump and  lots of carb adjustments.   In the end it matters not

 

 

 

I don't know where you read I was playing with an electric fuel pump and lots of carburetor adjustments. I have never mounted an electric fuel pump in my car when I owned it. 

[ACJCF2]

I am suprised no one uses a balance pipe between the carbruators  to help with smoothing out idle adjustment and overall run quality. I say this as I had an air cooled VW with twin carbs and could never get it run right. A VW tech. asked me if my manifolds had plugs, I said yes. He said I should have run tubing to them (a balance pipe). I sold the dub but put that tip in the memory bank.

 

Edited April 29, 2019 by ACJCF2
Grammer

[HotRodTractor]

On 4/28/2019 at 8:19 PM, ACJCF2 said:

I am suprised no one uses a balance pipe between the carbruators  to help with smoothing out idle adjustment and overall run quality. I say this as I had an air cooled VW with twin carbs and could never get it run right. A VW tech. asked me if my manifolds had plugs, I said yes. He said I should have run tubing to them (a balance pipe). I sold the dub but put that tip in the memory bank.

 

 

Most of the pictures in this thread are of aftermarket or modified stock intakes - they don't necessarily need a balance tube as they are already connected to balance out the pulses across the cylinders by the intake itself. Now the factory dual carb intake setup doesn't have the greatest transition area between the two carbs and actually has a factory balance tube to accomplish that.

 

 

 

 

[Adam H P15 D30]

Many factory tri-power set ups had the fuel lines split right at the front carb.

 

[ACJCF2]

That was interesting. Thanks for clarifying.