!952 Mercury with 255 Flathead V-8 Will Idle But Not Gain RPM.

[Chuckwin]

It is a completely original 6 volt car with the original "Teapot" style carburetor. The car starts and idles okay, but any applied throttle more than say 5 percent and the engine will stumble harsly and die if not released.

The coil is a known good. The voltage regulator has been replaced. The spark plugs and ignition wires have been replaced. The distributor has a new cap, rotor and points. I've used a known good condenser. The carburetor seems to being administering a decent amount of fuel, and adding fuel directly into the intake does nothing to alleviate the issue. The vacuum advance holds under a vacuum test. Messing with the range in the timing of the distributor does very little.


The car ran fine for some time before this problem began. I have unplugged all vacuum from the engine save the advance, although it does leak oil from the rear of the intake. Any advice or further questions would be very much appreciated.

[vincent]

Opening the throttle raises the compression. Therefor the spark needs more energy to ionise the air between the plug gap in order to jump and ignite the mixture. Wet plugs give a less resistant path for the energy down the porcellan so they tend to spark when out of the engine but will not when working against compression.

[Tony, NY]

Check for clogged exhaust pipe from a mouse nest.

[deuce5wndw]

Also check for clogged fuel line.

[Jake dalka]

More history would be good …but Tony, NY prolly is on the right track….

[RalphG]

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Is the accelerator pump working on the teapot? Mine is like that on the 52 Merc and I get around it by pumping the gas pedal a few good shots to supply enough gas to accelerate. Once its past that point it will rev up just fine. Going to get into that carb one day and try to improve on it but for now I can live with it.

[rotorwrench]

The idle circuit is just for idle rpm due to the placement of the ports very close to the throttle plates. As soon as the throttle opens off idle then the fuel is no longer drawn from that source as it transitions to the main flow ports in the venturi. The accelerator pump gives it enough fuel boost to keep up with the demand of the falling manifold pressure as the plates open up. There could be problems with the main circuit flow or the accelerator pump but as was mentioned previously, there has to be a constant supply from the float bowl to keep up with demand. The whole fuel supply system is involved with that demand for fuel so the pump pressure should be checked and the tank & lines need to be free to flow well. Venting of the tank and float bowl is also important as well as float bowl fuel level. If it has an automatic choke then it has to function as intended. There might be crap in the main jets or crud in the atomizer circuits. A clean carb is your cars best friend.

The ignition system in a stock Holley Load-O-Matic system is also involved with advancing the spark as the engine rpm increases. Any vacuum leaks in the carburetor/ignition system function can cause major problems in off idle function. A bad condenser will make spark erratic in all rpms including idle for the most part.

Always check the easiest thing first during the process of troubleshooting. The old teapots can be leakers so make sure the carb is in good condition. A fuel pump pressure gauge is good to have and a mityvac can test the advance mechanism in the distributor.

[Chuckwin]

I see. I would honestly like to do away with this carburetor. Would you be familiar with that process? I had heard the a a small base rochester is a match.

[40cpe]

The small base Rochester will bolt to your manifold, although the bore on the manifold is smaller than the carb bore. The manifold can be bored to a larger diameter. The vacuum on the Rochester is not compatible with the load-a-matic distributor. That can be cured with an after market distributor

[Chuckwin]

Is there a different intake I could use to fit the rochester? And I was considering going to electronic ignition, is that something you would recommend? I am trying to put some actual miles on this car and would like some reliability.

[Ggmac]

Agree , check for a blocked exhaust, next I would broken or frayed wire inside the distributor, the one that goes from the coil to the points . Its a 2 wire setup. I just yesterday did 2 replacement wires on 8 ba motors. Both wires were still attached but had frayed coating that when the point plate moved it shorted the ignition.
Its easier to remove the distributor to do this .
Do you have a vacuum gauge , if so use it and post the results. Good luck

[tubman]

The stock Mercury manifold and a small base 2G are about a good a match as you will find. It's almost serendipitous. Run the carb backwards and everything fits into place if you run an automatic choke. The only thing that needs to be "matched" is the choke linkage. Both the Merc and 2G come in "regular" (choke mechanism on the carb) and "divorced" (choke mechanism on the manifold) configurations. Match the carb type to the manifold and hooking them up is as simple as bending a rod (former) or shortening the heat tube (latter). As stated, the manifold should be bored out to match the carb (1 7/16"). I use a cutter called a "Rotabroach" and an old 2G base as a guide and do it on my drill press. One word of warning : 2G's have voids cast in the base for exhaust heat purposes. These voids are very close to the edge of the Merc mounting surface and can cause vacuum leaks. I made 1/4" aluminum plates that go beneath the carburetor to solve this problem.

If you would really like "some reliability", I would avoid an electronic ignition like the plague. While the car manufacturers have them down well, the aftermarket units not so much. Throw in 6 volts and the "dirty power" supplied by a generator/regulator system and sudden unexpected failures enter the equation. Because of their very nature, points ignitions fail over time and the signs are unmistakable. Keep your ignition system maintained properly with quality parts and "points will get you home". It's also a lot easier and cheaper to carry a set of points and a condenser than a complete distributor or even a module.

I have had this setup (a 2GC and a Mallory dual point distributor) on the '51 Merc in my '51 coupe since I installed the engine in 2016. It failed just one time and that was my fault as I was testing my 6 to 12 volt "Tach Driver" at the time. The "modern electronics" in the prototype failed and killed the points ignition. When I disconnected the device, everything was fine again.

New isn't always better.

[Chuckwin]

My distributor wire is frayed, will replace and see.

[Flathead Fever]

Just remember that it ran fine at one time with the parts that are on it. I would want to find the problem with the "defective part" before I would try other carbs or ignition. Will it run past the rpm that it stumbles at. Like others have mentioned it could stumble with a faulty accelerator pump but then it should run fine once the throttle gets past it. If you let it sit the gaskets and rubber diaphragms, go bad. It needs to be started every once in a while. With the engine "not running" pull the air cleaner and see if you see the accelerator pump squirting when you activate the linkage. If that is okay, then I'd pull the hose off of the carb and see how much fuel you're getting to the carb while cranking.

I inherited a flathead '32 roadster from my dad that has not run since he quit driving it, then he died and then so did his roadster. Just from sitting for years it now has a couple stuck open valves. It ran perfectly fine when he last drove it, (15 years ago?) I figure if I have to unstick the valves I might as well install a Clay Smith cam in it. I had a cam ground for it and a new set of "original" hollow lifters for it. I just have to many car projects to deal with plus I had a minor stroke. My son-n-law just asked me today if we could get the roadster going so he could drive it. This engine will start and idle but not great. Then it really falls apart when you give it gas. Definitely has two stuck open valves from sitting all those years. It's on my list of things to do.

[Pamlico]

My 36 LB flathead had the same symptoms, and it was a plugged orifice that feeds the accelerator pump well. Different carb, but same stumble off idle...

[flathead4rd]

Did you check the wire under the distributor plate? Sounds like it might be shorting out when the vacuum advance starts to rotate the plate.

[Ggmac]

Originally Posted by flathead4rd

Did you check the wire under the distributor plate? Sounds like it might be shorting out when the vacuum advance starts to rotate the plate.

See post 11 and 13

[rjlester]

I have the same problem with a Canadian 54 Meteor and a Flathead (Canada got the flathead one more year). It's a 255 and teapot carb. Automatic. The throttle shafts are worn and as soon as you step on the gas pedal, it stalls. Huge loss of vacuum out the worn shafts.

I put in a teapot from a standard trans car, with known good shafts, and it throttles up just fine and runs great. Only problem is, without a dashpot, it will stall sometimes under certain conditions, but this summer I'll hopefully find a dashpot that fits the standard trans teapot carb.

[Jake dalka]

Any progress to report ? …..