Mopar newbie in need of flathead 6 help

[1950Coop]

Been working on my 50 Plymouth Business coupe lately and started with the old falthead. It ran decent when we got it, but needed the carb rebuilt. I had the Carter 1bbl rebuilt, set the points to 15, split the factory exhaust manifold into duals and put it back together. Putting it back together, I realized that my split exhaust was very close to the fuel pump, so I removed it and installed a electric pump running about 4psi. When you first start it up, it runs terrible. Like it's running on 2 cylinders and missing big time. If I cup my hand above the carb and gently work the accelerator linkage it smooths out after about 5 minutes. Once it smooths out, it runs perfect and will start up everytime and run perfect as many times as you start it. Can't understand what would make it run so bad cold, but then run so good. Wondering if something is going on with this carb thats making it load up with gas or something. Any info will be greatly appreciated. Trying to get this thing ready for the Groundhog Gala coming up in Feb.

Thanks,

Jeff

[52b3b Joe]

Are you using the choke when starting it cold?

[1950Coop]

Are you using the choke when starting it cold?

Choke is manual, and doesn't seem to make a difference in any position. Are these motors pretty cold natured even in 80 degree temps?

[Rusty O'Toole]

IF everything is right your car should start like a modern fuel injection car, red hot or stone cold.

The only possible exception is some report vapor lock in very hot weather after driving for a while.

Something is definitely wrong. Exactly what, I couldn't say. But if the trouble started after the carb rebuild that is a good place to look.

I have found that you need to get the original factory manual, either from Plymouth or from Carter, and follow it exactly. Do not get ideas of your own, just cook book it together and it will work fine for you.

The typical instruction sheet that comes with the carb kit, is incomplete and filled with errors. In most carbs there are 4 or 5 adjustments that must be exactly right and of course, the carb has to be clean all passages blown out and all parts present and correct.

If the carb is right it pays to go over the ignition and recheck the advance, point gap or dwell, timing, and firing order. It is very easy to get plug wires out of place especially 3 and 4. Clean and gap the plugs. If they are very grimy get new ones.

And of course, you have to have good compression (no burnt valves).

There is no reason your car should not run like new if everything is right.

One more thing. When you install a free exhaust or duals, it is sometimes necessary to richen the mixture at full throttle, in other words a larger main jet. But you will be able to tell this by the spark plugs after you run it for a little while.

[james49ply]

cold running rough, then hot runs good, check the intake bolts, have had problems in getting them sealed, I have had to retorque them a couple of times. after the engine warms up the manifolds swell (expand) from the heat thus sqishing the gaskets a bit, then shrink when cold cousing the leak. put a wrench to the nuts/bolts when cold, see if they are a bit loose, carb base too.

[BobT-47P15]

Where did you install the electric fuel pump......at the front near the

engine or toward the rear near the gas tank. Don't know if it would

make any difference in your situation....but....they say that sort

of pump is a better "pusher" of gas than a "puller" - so should be

nearer the rear. Just thinking it might not be giving you enough

gas at first. (my un-educated guess)

[sunliner60]

have you removed the heat riser from the exhaust to the intake manifold?

[TodFitch]

Choke is manual, and doesn't seem to make a difference in any position...

That sounds strange to me. If the choke were functional then I'd expect that there would be a huge difference in how the engine runs, if it can run at all, in various positions of the choke control. Is it really connected properly?

[Young Ed]

I believe a 50 plymouth should have an automatic choke as OEM equipment. So if it truly does have a manual choke someone added it and its certainly a good idea to make sure it was added correctly.

[Harvey Tank]

I think he did when he split the manafold.

[yourpc48]

Some helpful suggestions?

Check your firing order

Timing

and Dwell.

Also make sure that the passages in the carb are clean. Did you rebuild the carb or did someone else? The new carb cleaners just dont clean the gunk out like the old stuff that would burn your skin off. I resorted to using etching aluminum wheel cleaner to clean my carb out but it was like new inside when I was done and it only took about 5 to 10 minutes to make the inside look like new. I also made sure that the metering rod piston was free moving in the carb. If the piston is stuck down there might not be enough gas flowing through. Be sure to pull all jetting and metering parts out. I cleaned out the jet and metering parts lightly with torch tip cleaners. Be careful not to enlarge the holes with the tip cleaners. My carb works great even though the car and carb sat for 25 years in a field before I got it.

Cant find the befores but here are some afters of the carb. The etching mag wheel cleaner works wonders.

[yourpc48]

Oh, Also if its cold out you no longer have a quick way of heating your intake after the split of the manifold.

I have personally experienced the carb base plate icing. Didnt make the car stop running but it can.

[dezeldoc]

If the choke is working it will be the same as using your hand. by using your hand you are making the mixture richer. look for vacuum leaks around the intake to head, carb base to manifold and hoses. Also it you have one of those thermal point and shoot heat guns use it and hit every exhaust port on the manifold and see if their is a difference, if so look towards those cylinders as the leaky ones. Most electric pumps are made to push not pull so the closer to the tank the better. Bad, old fuel will also cause these same symptoms.

[Reg Evans]

Been working on my 50 Plymouth Business coupe lately and started with the old falthead. It ran decent when we got it, but needed the carb rebuilt. I had the Carter 1bbl rebuilt, set the points to 15,

Thanks,

Jeff

The points should be set a 20.

[Don Coatney]

When the exhaust manifold was split was the flapper removed or welded in place (as pictured below) making it a true split?

[1950Coop]

Where did you install the electric fuel pump......at the front near the

engine or toward the rear near the gas tank. Don't know if it would

make any difference in your situation....but....they say that sort

of pump is a better "pusher" of gas than a "puller" - so should be

nearer the rear. Just thinking it might not be giving you enough

gas at first. (my un-educated guess)

Good thought...I put it at the front and never gave it a second thought.

[1950Coop]

When the exhaust manifold was split was the flapper removed or welded in place (as pictured below) making it a true split?

Don,

I removed the flapper completely. Never thought to leave it in and weld it up. Found that a big part of my problem was a pinhole in the fuel line. Electric pumps don't seem to like that very much. Not sure why it started running good after warming up, but it did.

[blucarsdn]

Don,

I removed the flapper completely. Never thought to leave it in and weld it up. Found that a big part of my problem was a pinhole in the fuel line. Electric pumps don't seem to like that very much. Not sure why it started running good after warming up, but it did.

During the early '50's I worked in a Hot Rod/Muffler Shop... We made all of the split manifolds we used right in our shop..

We always left the heat riser valve in the manifold, adding a plate with a 1/2" hole in the center on the split side which we welded in place.

Inline engines need heat risers to warm the fuel so the fuel will vaporize correctly.

Electric fuel pumps should always be installed as close to the fuel tank as possible... They push better than they pull.

Placing the electric fuel pump in the engine compartment also minimizes the fuel pumps ability to overcome vapor lock caused by high engine/air heat.