Inliners International Forums General Discussion Engines dual carb adjustment

Hey all, newbe here. I have a '58 chevy truck with dual carbs and fenton headers. The engine is rebuilt and I got it running again after letting it sit for over a year. What's the trick in tuning the carbs? I thought I was doing myself a favor by putting automatic choke carbs on it but they're a pain. How do I set these up? Also how does this setup effect the fuel mixture settings? Any advise would be appreciated.

Dear Mr. Flots;

This is easy to do.

With the engine stopped (cold) make these adjustments.

1). Adjust both the chokes wide open & lock them in place. There not needed with duals.

2). Turn both mixture screws in all the way & then back 1 & 1/2 turns.

3). Losen the linkage (or remove) so the throtle levers/controls are independant.

4). Back off speed screws till throtle plates are "at rest" closed.

Now; both your carbs are mechanicaly equal (adjustment wise).

Next; Turn the speed screws in EQUALLY about 2 turns +/- (opening) so engine can idle & warm up etc. To fast here is okay.

Once warm/hot; adjust the speed screws out EQUALLY till you reach the desired idle speed.

Now you can adjust the mixture on each.

To do this: turn in till you hear/feel a missfire (to lean) then back out till smooth + 3/4 of a turn each. This may take a couple of times.

Re-connect linkage.

Later; you can't adjust speed (idle) with the linkage attached, only mixture. There's NO high speed adjustment (external) It's your foot. :p

Good luck.

PS: Welcome to INLINERS Int.

Thanks John. I'll try it this evening.

So why aren't chokes needed in a dual setup? I was thinking I would need to run a copper line from them to the exhaust manifold.

I did run lines to heat the intake manifold.

You will only need one choke set on one carb.If both carbs are run at the same time and not on a progressive linkage. One carb set with the choke& it's high speed idle you will be fine.(Even in florida On It's cold days which not that offen. LOL)It will hold the high speed idle for both carbs. If you stop the chokes at wide open You will have to Hold the idle on your Own till it warms up enough to idle on its own.
At One event we had In daytona a Few yrs Back it was pretty cool/Cold that morning I almost wished My 3x4 tunnel Ram(450s) had at least one.The air was so cool My intake had some frost on it near the Base. You stock(low profile) intake may not need it BUT it can't hurt to at least set one carb up with a choke.

There just "excess bagage" on those set ups. Remember; you now have 2 idle ports with the same vacuum. They tend to stall (to rich) cold anyway W/O any choke.

If you had one with 3 carbs, then the center one is sometimes used (with choke) as the end idle mixture screws are turned in 'all the way' (off) and the engines idles only on the center carb and often has "progressive" linkage as Larry points out.

It works best (all around) this way and looks a lot clearner. You just need to warm up before driving, which is best anyway.

You can go either way with this and there are gains and losses either way. If you ditch the chokes you dont have worry about them sticking, you have less clutter and parts and less to go wrong.
On the other hand you will have wait longer for it to warm up and you will have to use your foot to hold it at high idle, there are some set up's that will not stay running for warm up with out a choke(esp.in cold weather).
But with Rochesters in Florida you won't have to much trouble, so if your chokes are more of a pain than the warm up thing.....take them off.

Dan

Auto-chokes on some carbs need to be connected for the carb to work properly. And both on a dual carb set-up.
Best to convert to manual choke with the universal conversion kit available at NAPA for around $20.

I run a dual carb setup for many years every day with one permanently open choke and the other connected.
Helps starting during the colder and freezing months.

Also get a 'uni-syn' tool when balancing multiple carbs. It helps getting the carbs synchronized as close as possible.
The smallest variation can make a big difference in response and fuel economy.
Uni-syns are available on ebay all the time.

Still messing with it. I have noticed it runs considerably better with the air cleaners off. Enough to make me wonder if I don't have enough vacuume or if my air cleaners are too restrictive. The ones I'm using came from a swap meet that I found a paper filter to fit.(filters are about 7" dia x 1.5" tall. Anyway to increase vacuume?

What is the vacuum reading and your right, the filters shouldn't change a thing.

Either way you need to get the throttle plates equal.

It's easy, you'll get it.