Engine: 2 Carb balance 53 6 cyl with Offie manifold

[dand1]

Does anyone have any guidance to my 53 Champion K body restorer on how to balance the mixture ratio vs speed with the 2 carb set up on top an offie manifold.

My problem is: very hard starts; ok low range drive ability, 50-60- MPH stalls or floods. Seems too much gas or too little air and is non linear over load range; too much air at start and too little air at high speed. I suggested using a dyno to collect measurements but have been ignored by restorer; is part of the problem the small diameter air cleaners on top of the carbs?. Anyone have ideas or suggestions.

Dan De Haven
ddehaven@cox.net
703.470.1300

[jclary]

Hey dand1, welcome to the forum.
(and...dang it, I hit the wrong button and sent a post out before I meant to.)

Unfortunately, I can't help you on your dilemma by qualified knowledge or any experience with a set-up as you describe. I'd be interested in what some of the modifiers and very qualified mechanics that populate this forum have to say. First, I'd like to know if you have made additional modifications to the engine before slapping a two carb manifold on it. For example, does it have larger pistons, valves, hotter cam? If not...the engine was designed to run just fine on one carburetor. Seems to me, that unless something else was changed, then, all the settings for two carbs would require "half" the settings for "one" carb. That would be my ignorant instinct for settings on two carburetors put on an engine designed for only one carburetor.

Anyway, I think you posed a good question and I hope some of the real mechanics will educate us. Again, welcome to the forum and hope you enjoy our group, and hang out from time to time. Also, post some pictures. Even if it runs crappy...two carbs always look cool!

[DEEPNHOCK]

Dual carbs 'usually' only run one choke....
'Balancing' dual carbs is 'usually' done with a synchronising tool.

I've had a uni-syn tool for decades, and pull it out evey time I see a dual carb setup.
Simple to use...
Amazon sells an Edelbrock knock off of the Uni-Syn...

http://www.amazon.com/Edelbrock-4025-Carburetor-Balancing-Instrument/dp/B00062YC2E

[LeoH]

Also try asking on http://www.racingstudebakers.com

[sals54]

DEEPNHOCKs got it right. Get the UniSyn. Done right the first time will give you many miles of trouble free driving.

[jozek]

If you would like an 8 to 1 compression head to go with those carbs, pm me.
Good luck with your sync job.

[Mike Van Veghten]

Yep...again, what Jeff said.
I've used them MANY times over the years on cars and bikes. Sometimes it takes a work to get the Unisyn adjusted for the airflow, but if you go slow the first time, they are easy to use.

Mike

[t walgamuth]

A picture of the manifold is needed to understand how the carbs are supposed to function. Are they completely separate on it and one carb feeds certain cylinders or is the air fuel passage connected and they are set up with a progressive linkage. Generally a carb is something through which air flows and fuel is added. It should work over the range of rpm if everything is working as it should. So generally the mixture screws should be set similarly on both carbs I would expect, unless they are a progressive set up.

[Dick Steinkamp]

My guess is that you have some other problem rather than a simple balance of the two carbs...but start with that.

I'm assuming that this is not a "progressive" set up and that the carbs are exactly the same, newly rebuilt, and the same or similar to the original single carb.

The purpose of the balance is to insure that the throttle plates in both carbs are open the exact same amount at idle so that when the linkage starts opening the throttle plates, that they will be open the same amount at all throttle settings. (If you have a progressive set up, a UniSyn is not needed since the throttle butterflys are opening at different rates. I've never seen progressive linkage on a 2 carb set up but they may exist) The UniSyn does this by measuring the air flow through the top of the carbs. You disconnect the linkage to the carbs, then adjust the idle speed screw on each carb until you are seeing the same reading on the UniSyn for each. This is an iterative process since you are also dealing with idle mixture and idle speed at the same time. Once set, you reattach the linkage making sure that it is re-adjusted so that it just slips into place and does not disturb the idle settings you just set up.

Once you do that, I would check to make sure visually that the carbs are reaching WOT at the same time by looking down the throat of the carbs and slowly moving the linkage to WOT (engine off of course). If the geometry of the linkage is not correct and one carb reaches WOT before the other, the car will never run right.

I would not run chokes on either carb. For a tri-power set up, it is common to run a choke on only the center carb since tri-powers are generally progressive and start only on the center carb and run only on the center carb until warm. On 2 carb set ups, the car starts and runs on both carbs all the time. To have a choke only on one carb means one carb will be quite a bit richer than the other carb until the car warms up. Not a good thing. The car should start just fine without chokes with a couple of pumps of the throttle. You may have to bump the throttle a little until you start generating some heat if it is cold out. If it does not start with this process, you have something else wrong (accelerator pumps not working or adjusted improperly, timing off, weak ignition, low compression).

If you are still experiencing the same problems after doing the above, you'll have to dig deeper. Carbs rebuilt properly? Float levels set correctly? Accelerator pumps working properly (if adjustable, try different stroke settings)? Vacuum leak? Ignition sharp? Timing correct? Advance mechanism working properly? Valves adjusted too tight? You may want to put the single carb and manifold back on the engine to trouble shoot the bad running to eliminate the dual set up as a factor until you have the engine running right.

On this engine, I had two stock two barrel carbs on a bone stock 259 CID engine. Straight throttle linkage (not progressive). No chokes.



It started easily, idled like a stocker, and ran as good or better than with a single carb...

[PackardV8]

My problem is: very hard starts; ok low range drive ability, 50-60- MPH stalls or floods.

My guess is that you have some other problem rather than a simple balance of the two carbs...but start with that.

X2 with Rich. The Uni-Syn only balances the idle settings. If it won't start and stalls or floods at 60 MPH, something else is going on beyond idle adjustment imbalance.

1. Is there an electric fuel pump? If not, adding a small electric pump (DON'T use the hot rod Holley/Carter high pressure/high volume pumps) would be my first suggestion. Having the fuel bowls full solves many hard starting problems.

2. Who built the carbs? Exact same part numbers and jetting verified? Correct float levels? the throttle shaft bores rebushed? The majority of Strombergs I see have worn throttle shaft bores.

3. Has the distributor been professionally rebuilt and the vacuum and centrifugal advance curves verified? What initial advance?

4. Single or dual exhaust? Heat riser valve installed below the exhaust manifold? Is it free and operating correctly?

jack vines

[Mike Van Veghten]

What Dick says is basically true.
But this check is NOT to verify that the throttle blades are exactly the same. It's to make sure both carburetors "flow" the same amount of air at idle. There are many reasons that having the same throttle opening will not provide the same airflow.

Also, the best way of beginning this setup it to "try" to run the idle mixture screws off of "ONE" carburetor. If possible, it's MUCH easier and more accurate.
Two things will tell you if you cannot...
1. you just can't set the idle, (very unlikely).
2. you have a hesitation at hard throttle (slight possiblilty).

If either of these things happen, then you may need to "crack" open the second carburetors mixture screws.

Just as verification...ALL...factory tri-power and dual quad arrangements, only have one carburetor as the idle mixture carburetor..!

Additionally, if you want to be even more accurate with the ballance task, the "mercury tube" tool used for tuning motorcycle engines is more accurate thAn the Unisyn. But the Unisyn is just fine for most applications.

Also...for what it's worth, the twin single barrel assembly can be setup either progressive or open both carb's. at the same time. This is because of the single "log" manifold.
But the ballance still needs to be very close in either case.

Mike

P.s. - If the butterfly shaft in either carb. is too loose...you'll have a hell of a time getting a good idle every time the throttle is closed.