Flathead Distributor - 39 Ford

I have a 39 Ford flathed with Edmunds dual intake (with 94's) and Sharp heads.

We have tweaked and tweaked the carbs. The engine idles fine, but just dumps too much gas when under load (trying to drive it) - It coughs and backfires as if too much gas is in the cylinder after firing?

Its almost as if the advance is not working? The distributor is the divers helmet type, which is not easy to advance timing on. Any ideas?

I have read a lot of posts on the HAMB on dual carb set ups and such. I am wondering what is the best solution and if it carb or distributor problems.

Has anyone used electronic distributor for this year Flathead. BubbaGMC's distributor converstion is for 2 bolt only. What about Mallory? They seem pricey. Any suggestions?

Thanks, Casey

 

Casey;
Check your fuel pump pressure. Should be 5-8 lbs. pressure. With an old pump, the by- pass valve will stick or get gummed up, and your pressure increases. That will over power your float valve and flood. I've seen it happen lots of times, and most people don't check fuel pump for excessive pressure.
Good luck
Steve

 

Fuel pressure should be less that 3 #'s for your flattie. The vacuum brake may need adjustment it sticks out at an angle on the dizzy and has a 7/16" or 1/2" head size bolt with lock nut. Loosen locknut and screw the bolt in one turn and drive it. If it doesn't ping under load turn it in another turn. This adjustment advances the timing. Once you get it to ping back it off 1/2 turn.

Jim

 

Start with one carb (preferable a known good one) and figure out if there is a ignition problem.

Then use one of the carb's and then the other to check them out.

IF OK

Then put everything together.

 

Running with Holley 94s, you need a power valve with a lower vacuum setting (inches of mercury) with duals a "4in Hg" would be better than a "7in Hg" that most carb kits come with. Otherwise they dump too much fuel under load.

 

We have a fuel regulator to the carbs - we dialed it down to 1.5lbs and it still floods (this is the first thing we tried since we were using an electronic fuel pump).

 

I didnt know the divers helmet dizzy had a vacuum brake bolt. Truck is at the shop, so I will have to wait for monday to look and see. Thanks, Casey

 

Rotowrench has the right answer I think. Try driving it with one carb blocked off and I bet it will run a lot better. Just put a cardboard blockoff under one of the carbs and unhook the linkage.

The double power valves is dumping to much gas under load.
also check your float level It may be to high.

Your distributor doesn;t have a vacuum advance It has a vacuum brake (retard) that kicks in under load.

 

The only way to properly check out that distributor is on a dist machine. May not be advancing. As others have stated, run one carb at a time. Too many variables to evaluate at one time.

 

Casey I ran across this article in Hot Rod mag, about Holley 94's flooding out in dual carb situations.


At this point the obvious question is, "What's the big deal with using 94s?" The main issue is the vacuum-controlled power valve. Every carburetor has some sort of enrichment system to supply more fuel when the engine requires it. Typically that's when the engine is under a heavy load, such as full throttle acceleration, passing, pulling a steep hill, and the like. In all these situations, the throttle is open and as a result the manifold vacuum drops. Holley 94s used a power valve (also called an economizer valve) that opened to supply extra fuel to the engine when the vacuum dropped to a certain point, usually 7.5 inches Hg or less (the opening point is indicated by a number stamped in the housing). The problem is that when two or more carburetors are used, the vacuum signal drops earlier and more aggressively than with a single carburetor. As a result, the power valves open prematurely, making the mixture much richer than necessary. A common mistake in this situation is to re-jet the carburetors--that results in even worse driveabilty problems. Another mistake often made is to plug the power valves, something that we don't recommend. The best approach to this problem is to stick with stock jet sizes (or very close) and use power valves that open at a lower value. In the past with dual 94s, we've used 3.5-, 4.5-, and 5.5-inch Hg valves, depending on the cam used, with excellent results.

 

Too many variables is right - we have to start eliminating them one by one. Thanks, Casey

 

Thanks - we will look into this next. Thanks! Casey

 

Is it one of the cheap chrome round dial-a-adjustment regulators?