Flathead V8 Problem

[wolfords]

I have a flathead V8 8BA engine with two Holly AA94s.

If you let off full throttle then it's okay (like at quarter throttle), but when you accelerate beyond that it acts like it's starving for fuel or the advance isn't working (but the advance is working). I've had both carburetors rebuilt, messed with the timing, put a new blue streak coil on it, messed with the jets and I'm running the factory distributor. It also smells rich at idle and acts lean on top end.

Any ideas?

[flatheadmurre]

Start by putting a vacuum gauge on it.
This will tell you what powervalves to aim for.
To big number powervalve and you have rich condition on idle/cruise.
Real hard to tune an engine on distance.
Get an Air/Fuel gauge and install it in the car takes a lot of the guesswork away.
Fuelpressure gauge is also in my setup when tuning an engine.

[mfirth]

You said "factory distributor"...if you mean the stock Load a matic, there is your problem.
Lots of threads on this by people much smarter than me.
Try bubba, charlie new york, & tubman....they have solutions! m

[Frank Miller]

Originally Posted by mfirth

You said "factory distributor"...if you mean the stock Load a matic, there is your problem.
Lots of threads on this by people much smarter than me.
Try bubba, charlie new york, & tubman....they have solutions! m

He says the advance is working but I wonder how he knows. If it is advancing the curve may not be right.

[OhioRick]

A bad condenser will have this symptom.

[richard crow]

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do you have those little air filters with the paper element remove them & try it

[revkev6]

as others said, the distributor is not able to advance correctly with multiple carbs. you need a single ported vacuum signal for it to work as it should.

to test, disconnect and plug the vaccum, manually set the timing to 14-18 degrees and take it around the block. timing will be locked with no advance when you disconnect the vacuum. if it runs better, get a distributor that doesn't use ported vacuum. bubba makes electronic conversions, and many others sell mechanical advance units.

[chap52]

Just FYI: I am running an 8BA with two 94's, a Howard M6 cam and with Bubba's converted GM distributor. Also along the way Charlie NY advised me to block both Power Valves. I balanced them using a Uni-Sync and I experience no stumble or studder. This worked for me. Chap

[wolfords]

Who sells mechanical distributors? Thanks for your help.

[john in illinois]

What do your spark plugs look like? Sooty or tan or white?

John

[chap52]

Try Bubba's ignition for distributor and info. The GM conversion distributor I am running is mechanical.
Great guy to work with (Jim Linder) and always willing to answer your questions.

[Steve/IL]

Check the gasket under the top cover of the fuel pump and at the bolt. If they aren't sealing properly, the pump will not generate enough vacuum to pull fuel through the pump essentially starving the carburetors on acceleration or under load.

I chased carburetor, distributor, advance and coil problems and vacuum leak problems at the carbs for a year before change the fuel pump upper gaskets. The engine now starts better and runs fine.

I'm still using a cork gasket under the cover. Does anyone make a fuel resistant rubber gasket for the fuel pump upper cover??

[3blapcam]

Originally Posted by wolfords

I have a flathead V8 8BA engine with two Holly AA94s.

If you let off full throttle then it's okay (like at quarter throttle), but when you accelerate beyond that it acts like it's starving for fuel or the advance isn't working (but the advance is working). I've had both carburetors rebuilt, messed with the timing, put a new blue streak coil on it, messed with the jets and I'm running the factory distributor. It also smells rich at idle and acts lean on top end.

Any ideas?

Like others have said, stock distributor is a "no go" with multi-carbs. It doesn't receive the correct vacuum signal to function properly. Bubba's, Pertronix or maybe find a Mallory dual point mechanical advance. Bubba's will steer you right as he is very knowledgeable about early distributors.

Once you get that sorted out, then you can figure out what your fuel pressure, PV's or plugs, etc. and go from there!

Good luck!

3blap.

[flatjack9]

I have Charlie, NY build my conversion distributors. Can't beat-em.

[Sid]

Are you running power valves in both carbs.? As posted earlier check manifold vacuum divide that number by 2 and go with that power valve. (15 in vacuum would = a 7.5 power valve etc. Also only run one power valve. Second power valve should be plugged. Also on the second carb. idle screws should be turned all the way in and throttle blades should be completely closed. The second carb is only a (dumper) Vintage Speed in Daytona Beach Fl. has base plates designed for this omitting the idle screws and and throttle closes completely. You also need to watch some power valves that come in the kits as the tip at the end is too large and interferes with the housing. Late Holley power valves do not work on Holley 94'S. Hope this helps.

[Tinker]

On a two carb 8ba I'd lose the vacuum distributor for sure. Not sure how you would make it work well otherwise. Charlie can handle it, no issue, or get a chevy conversion from bubba.


Then work out your 94? 97? carb issue. They make vacuum carb sync equipment available if you need.

[marko39]

Originally Posted by wolfords

Who sells mechanical distributors? Thanks for your help.

Mallory has an electronic dist. with just mech. advance. i believe it is 12 volt. Mark

[tubman]

I would avoid an electronic distributor, especially with a 6 volt system. A points distributor doesn't care about voltage; the coil does. Also, beware of new Mallory flathead distributors. They have been known to come with SBC advance curves that are too aggressive. My personal opinion is that if you want to go with a Mallory dual point, get the best older unit you can find, either an original flathead unit or one for an SBC which can be converted for use in an 8BA.

[flatjack9]

Originally Posted by Sid

Are you running power valves in both carbs.? As posted earlier check manifold vacuum divide that number by 2 and go with that power valve. (15 in vacuum would = a 7.5 power valve etc. Also only run one power valve. Second power valve should be plugged. Also on the second carb. idle screws should be turned all the way in and throttle blades should be completely closed. The second carb is only a (dumper) Vintage Speed in Daytona Beach Fl. has base plates designed for this omitting the idle screws and and throttle closes completely. You also need to watch some power valves that come in the kits as the tip at the end is too large and interferes with the housing. Late Holley power valves do not work on Holley 94'S. Hope this helps.

This is fine if you are using progressive linkage. However I do not recommend this kind of setup. Run both carbs with straight linkage.

[wolfords]

Thanks for all the suggestions. It sounds like it's power valves and distributor. Both carburetors have 7.5 power valves. I ordered smaller ones to put in this week. Everyone says I need a mechanical distributor. This is an original 6 volt. I don't want to put electronic on it. I need an old Mowery. I'll keep checking. Thanks again!

[Ol' Ron]

If you have a stock 8BA engine then you can't use the stock distributor. The carbs should have stock power valves. To prove a point, Remove one carb and block off the base. Engine should rune OK under all conditions. If not, you have other problems

[Sid]

Originally Posted by flatjack9

This is fine if you are using progressive linkage. However I do not recommend this kind of setup. Run both carbs with straight linkage.

The info. I gave was for straight linkage. I also think you need a pretty wicked flatty to run power valves in both carbs. That's why you block off one power valve on multiple carb. set-ups.

[flatjack9]

Don't agree at all.

[estout81]

I run power valves in both my carburetors. Runs well.

[Tinker]

Run 3.5s power valves in a dual 94 with all in dump. chevy conversion distributor. just my opinion.






.

[Flathead Fever]

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Originally Posted by richard crow

do you have those little air filters with the paper element remove them & try it

Richard is right. I had brand new ones change my idle speed. If they can restrict it at an idle imagine what they do at road speeds. You can try driving it without them (if you have those).

[Flathead Fever]

Originally Posted by Frank Miller

He says the advance is working but I wonder how he knows. If it is advancing the curve may not be right.

Frank asked how you check total advance. You use an "adjustable" timing light and a hand operated vacuum pump.

Disclosure I'm not a flathead guru. I know enough to hold a conversation but I'm not an expert. I was a professional mechanic so I know how things work. There is nothing magical about a flathead (except the sound)

Something I like to do is try to get "car people" to understand how these systems work. You can't work on them if you "don't" understand how they work! Most car people" think they know but they don't really understand what is happening. A lot of the "paid" mechanics don't know either, especially in hot rod shops and antique auto restoration shops. They are restorers (I use that loosely) they are diagnostic mechanics. The problem with your engine could be either fuel of ignition, which you already know. For now I'm going to discuss the ignition.

Checking advance, you check the mechanical advance with the vacuum advance line disconnect and plugged. Then you compare the mechanical advance to the rpm. You can watch it move with a timing light. You compare it against the factory specifications up to the point you reach maximum mechanical advance. This is done while your looking at the pulley's timing mark while you turn the dial on the timing light which moves timing mark back to your base timing. Then you read the degrees on the timing light and you can tell how much advance you have. You have not changed the actual timing but changed when the timing light flashes. The dial on the light tells you how many degrees in crankshaft rotation you have altered the flash.

The mechanical advance can become stuck or the springs get can get weak causing it to advance to fast. You will able see all of this with your adjustable timing light.

Next the vacuum advance. At an "idle" you apply vacuum to your advance with your hand pump until it reaches maximum advance. You do not want the rpm above idle because then the mechanical advance will start to kick in and you only want to see the vacuum advance reading. Move the dial on the timing light just like you did before and this will tell you what the vacuum advance is capable of. The combined base timing, mechanical advance and vacuum advance will give you your total advance. Do "not" buy a timing light unless it has a way to measure advance. I just picked up a really nice one in the box at an estate sale, dirt cheap. The new ones are digital with buttons instead of the dial.

Lets talk about that vacuum advance on a '49 to '53 flathead and any other engine equipped with one. Not the earlier 59A style distributer, that is a vacuum brake system and works completely opposite the way the later flatheads work.

The vacuum advance does not work the way most people think it does. Even most mechanics don't know since everything is computer controlled now. It was not designed for a high performance engine. A good example is the Ford 289 engine. All the 289s came with a mechanical and a vacuum advance distributor "except" for the factory hipo 289, 427 side oilers and few others. They only have a mechanical advance, why would the engineers have done that? The vacuum advance is not there to make more power its there to prevent detonation under a heavy load like climbing a hill. Going up a hill you have your foot mashed to the floor so the maximum amount of air and fuel is being drawn into the cylinder but the RPM is not very high as engine is being bogged down. If it were to receive the maximum ignition advance at the same time the mixture would detonate, "engine knock" because the engine is rotating to slowly to receive the spark that early.

To prevent detonation they installed the vacuum advance. Now you need to understand how engine vacuum works. At Idle vacuum is high because the throttle plate is closed. The engine is sucking against the bottom of that plate. If you hook a vacuum gauge to a port "below" the throttle plate (manifold vacuum) it will give you a high vacuum reading on a engine with good compression and a stock camshaft. As you open the plate the vacuum begins to drop because you are reducing the restriction. A partially open throttle plate would be typically be when you were cruising down the road. The vacuum advance receives its vacuum signal from "above" the throttle plate (venturi vacuum), because we don't want it advancing at idle which it would if it was connected to a vacuum source located below the throttle plate. As that throttle plate opens there is now vacuum above the plate which is sent to the vacuum advance which advances the timing. You now get better power and better gas mileage because the increased timing produces more pressure on the top of the piston. That is why when you advance the timing at idle the rpm goes up, more pressure (weight) is pushing down on the piston so it moves faster.

Your cruising a long and now you reach that hill and the engine starts to lug down. You push the pedal to the floor. The throttle plate is now wide open. There is no restriction and vacuum drops to zero. There is no longer a strong enough vacuum signal to operate the vacuum advance and timing retards. Retarding the spark, making it happen "later" reduces the pressure on the piston and prevents detonation. These engineers were no dummies. That was a brilliant idea!

On a hot rod engine we do not want the timing to retard when we mash the pedal to the floor. We want to create the most pressure on the top of that piston as we possibly can without blowing a hole through it, more pressure more power. So we run a mechanical "advance only" distributer that can produce the most advance the engine can take without detonating. Detonation causes a loss of horsepower. We prevent the detonation by using higher octane fuel which burns "slower" than low octane fuel. The low octane fuel (regular gas) actually has more power than high octane fuel but not as much power as a high compression engine, with advanced timing running on high octane fuel. That's the trade off.

Your actually reducing power when you put high octane fuel into an engine designed to use regular gas. Not only does the high octane gas have less energy it changes the timing of your engine. It burns slower so the maximum pressure will not be achieved when the piston is at Top Dead Center.

Even after the 8BA flatheads came out in 1949 hot rodders continued to use the older flatheads with the mechanical only advance distributers. They could not create as much power with 8BAs vacuum advance style distributers. It took a little while for the aftermarket industry to make a mechanical only distributer for these later flatheads. You will here a lot of old-timers swear by a 59A engine There is no way they will use an 8BA engine. Its not because the block was any stronger. It had to do with those late model distributors. Those guys that tried to make power with them still hate them to this day(my 88 year old dry lakes racer neighbor).

One of the things you can try is to remove the vacuum advance line from the advance unit and plug it. Then hook up your hand operated pump with a long enough hose to reach inside the car. Then you can apply what ever vacuum you want, at any rpm or load to your distributer just to see what it does. Do this kind playing around with stuff. Its not going to make since reading about. It will stick in your head forever once you put your hands on it.

Another thing, a lot of vacuum advance are adjustable but I don't know about flatheads? When you remove the hose you can stick an Allen wrench in that vacuum port and adjust the advance limit.

[tubman]

I have purchased two "Advance" type timing lights and neither worked properly. Just a heads up.