Can’t get 8BA idle fast enough

[AnthonyG]

Hi all, been noticing last 3 or 4 excursions my idle is to slow & car easily stalls as a result. Running 2 Holley 94’s rebuilt a few years ago by Charlie NY. I’ve used up all the thread on the idle screw. Car runs great on acceleration, running @ steady speed. If I give a little choke it idles / runs fine. Ideas?

[Ronnieroadster]

Originally Posted by AnthonyG

Hi all, been noticing last 3 or 4 excursions my idle is to slow & car easily stalls as a result. Running 2 Holley 94’s rebuilt a few years ago by Charlie NY. I’ve used up all the thread on the idle screw. Car runs great on acceleration, running @ steady speed. If I give a little choke it idles / runs fine. Ideas?

Sounds like the two carbs are not tuned as one. Have you tried synchronizing both Carbs with a unisyn gauge? Also have you set the idle mixture screws on each carb using a vacuum gauge?
Ronnieroadster

[aussie merc]

with ronnie also check fuel pressure at the same time

[AnthonyG]

Thx for replies! As I understand using the unisyn gauge is used if carb linkage locks the carbs together as one. I have mine running on the rear carb & progressive to front one. Based on instruction videos seems unisyn gauge is for the non progressive setup? Could b pressure, what psi should fuel delivery be. Mechanical fuel pump is fairly new. Couple thousand miles.

[AnthonyG]

Seemed fine last season. I was thinking maybe timing? Long story but I have a crab style electronic Speedway Distributor on front face of engine. Vibration might’ve let to turn a bit. I’m not sure which way engine rotation would naturally turn Dist if loose but remember when timing retarding slowed idle & advancing increased. I was thinking if the natural rotation of Dist if loose were in direction of retarding ( as I remember counter clock wise rotation of Dist) that might be it?

[cadillac512]

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Have you tried setting the idle speed screw in just a bit more on the front carb? Also, if the front carb has any idle circuit problems (lean) it might be affecting your settings. I'm assuming the front carb does have the idle circuit operational.


Terry

[flatjack9]

The distributor turns counterclockwise, so rotate clockwise to advance.

[Ronnieroadster]

Both carbs should be adjusted to be equal at idle. The front carb idle setting screw might be the problem.

Running progressive would not change the fact both carbs need to run equal. When we set up a two or three deuce' set up on a flathead with or with out progressive linkage the carbs are set so they all idle as one each pulling the same amount of air. Using the Unisyn to accomplish the adjustments.
Ronnieroadster

[Flathead Fever]

The unisyn gauge is to insure both carbs are opened exactly the same amount at idle so that all cylinders receive the same amount of air and fuel "at idle", right now they are not doing that, half the cylinders could be starving for fuel depending on the design of the intake. The progressive linkage is for the off idle circuits "not" the idle circuits. You need to start all over again with your adjustments.

But first, timing must always be set before adjusting the carbs. If it has points, the dwell is set first, then the timing and last is the air fuel mixture and idle speed. It "must" be done in this order. Because, if you change the timing it changes the air fuel mixture, and you have to go back and adjust the carbs. Adjusting the carbs does not change the timing so the timing is always done first.

Remove the linkage from the carbs. Make sure each carb has a return spring, without them when you start the engine the throttle plates can fly open to wide open throttle. Back off the fast idle screws for the choke so they are not holding the throttle open Back the idle speed screws out and then turn them back in until they just crack open the throttle plates. Turn the mixture screws in and then back them out 1 1/2 turns. Hopefully it starts and idles. Then you synchronize the throttle plate openings with a unisync. Then you go back and forth between adjusting the air fuel ratio and the idle speed until both carbs have identical settings. I use propane to check the air fuel mixture at idle. If I give it a little propane and the idle goes up, I know the engine wants more fuel. If it goes down, I know it's already getting too much. If the idle does not change I know I'm real close and I give the air fuel mixture screws another 1/8" turn out to the rich side to compensate for daily atmospheric changes. Better to be a little rich than lean. You have to go back and forth between adjusting the air fuel mixture and the idle speed too make both carbs the same. In theory, both carbs air fuel mixture screws will be turned out the same amount and both throttle plates will be opened the same but there are slight flow differences that might make their adjustments a little different. When the carbs are finally adjusted so the unicyn reads the same on both carbs and the addition of a little propane has the same effect on both carbs your good. Attach the throttle linkage. You adjust the linkage to slip onto both carbs without moving the throttle plates or you will mess up your synchronized throttle plates openings. It sounds more complicated than it is.

With just two carbs I would try your engine without the progressive linkage. You still have other changes that need to be made. You need get the power valve and the main jets the correct size. You need to get the accelerator pump stroke adjusted. All that has to be done to achieve a nice crisp engine response when you open the throttle. It takes a lot of experimenting to get it correct.

I bet 90% of the people slap a carb on and never get it setup correctly because they are afraid to mess with it. Study up on how each circuit in a carburetor works They are simple if you break them down into the individual circuits. Here is a good article. It's about 4-barrel carbs but they all work about the same. There are seven circuits that each need to be calibrated for an individual engine.

https://www.hemmings.com/stories/art...-lost-art-of-2

[AnthonyG]

Thx guys, will do all of above.