1953 M37 Carb Flooding. Assistance needed.

So if I understand things correctly you have tried 2 carbs one being rebuilt and one from VPW both with the same results. You have the correct base gasket. So to me that rules out the carb as the problem. One thing you said is that the flooding is instantaneous and based on your description is also copious. That to me says fuel pump(s). I would get rid of the electric pump and current mechanical pump if it is still in place and get a replacement mechanical pump. The ONE that actually is called for with the M37. If you have the OEM dual diaphragm pump body you can get a rebuild kit from an outfit called Then and Now Automotive. www.then-now.com they have rebuild kits designed for fuels with ethanol so the soft parts do not degrade over time. Kits are $70.00. You can also send them your pump and they will rebuild it. A lot of guys do not want to spend what a NOS or quality rebuilt pump costs and go with the electric pump or pump found on the industrial version of the Dodge 230 CI engine. I have seen a lot of postings dealing with fuel and pump problems. When I did my frame off restoration I stayed strictly GI and have never had a problem. No flooding, no vapor lock, no hard starts. Last, though this is a shot in the dark make sure your gas cap is properly vented.

Thanks for the reply Gunny, I have tried 2 carbs, there was an E7T2 carb on there running off the electric fuel pump before it sat up and it ran great. Also, whenever I set the carb off to the side and turn the fuel pump on there is no flooding issues, it's only when I engage the starter with the carb in place, I was trying to get it running before spending more money on a fuel pump, I do have the original double diaphragm pump on the block but it has been bypassed. All of the bypassing was done before I got the truck.

Another troubleshooting step I have done and forgot to mention was I filled the carb with gas via the fuel pump, then disconnected the fuel pump and tried to crank it up and it still flooded even without the fuel pump physically connected, I have not tried this with the 2nd carb though

sounds like float is sticking

And if you are using a elect pump make sure it is for a carb. should not have more than around 7psi

I went back and looked at all of your pictures.

Was the Crankcase vent tube removed before the flooding started or after? I see that you mentioned leaving it off since it keeps flooding.

Since you have tried two carburetors with the same flooding issue it would lead me to believe its not the carbs. (Highly unlikely they are both not set up properly)

Have you put a pressure gauge inline with the electric fuel pump yet? (4-6 PSI is what you are looking for) I have had better luck at the mid to low end of that range.

When you looked at the base gasket, did you put it against the bottom of the carburetor and visually inspect that you could see the vacuum ports on the base with zero obstruction? (The two base gaskets with the X pattern are very similar but the one with the smaller X will restrict vacuum)

When you are trying to start, do you have the choke set and no additional gas pedal applied?

Things to help further diagnosis flooding issue(depending on the answers to the above questions):

1) Since the fuel bowl vents through the tube before the choke plate, fill the fuel bowl again then disconnect fuel pump and try starting wile having someone watching the bowl vent for fuel gushing out.
A) If fuel is seen flowing from this tube the float is set incorrectly. (5/64" is a good starting point)
B) If no fuel is seen flowing from the vent tube, see step #2

2) I would connect the Crankcase PCV valve system. The open port to the intake is causing a vacuum leak.
A) The carburetor Pump Circuit is Vacuum / spring operated. (Under constant throttle, vacuum holds the plunger up. When the throttle is suddenly opened the vacuum drops and the spring pushes the plunger down forcing fuel into the throat of the carburetor.)

I wonder if the open PCV vent line to the manifold is causing the pump plunger to flutter and dump excessive fuel down the carburetor throat.

I will post more ideas once I see answers to the above questions.

Bert

When it first started flooding I removed the crankcase vent tube to try to prevent gas pouring into my crankcase, that was with the carburetor I rebuilt, that is an absolutely great idea to put it back on to prevent a vacuum leak, that never crossed my mind. I did put an inline pressure gauge after I put the pressure regulator on and it is putting out about 1 lb until I get the flooding under control. I also went ahead and purchased a new rebuild kit today from then and now to put the original fuel pump on there. I'm going to kick myself if crankcase vent tube fixes the problem. Yes I also made sure the base gasket was not obstructing any ports and I have not used the choke or the throttle when trying to start. I will put the vent back in place this evening and give that a try and let you know. Just curious, since I removed the original fuel pump from the side will it still be safe to start without it in place? Thanks for the help once again.

The fuel pump is actuated off a lobe on the camshaft with no push rod. Should be fine but you may want to put a shop rag into the opening to reduce oil splash from the hole.

A word of caution about running the engine for more than a few seconds if gas has thinned the engine oil.

Bert

Well, I reconnected the crankcase vent and she is still flooding, seemingly worse, I know not to run it long with gas in the crankcase, I have already changed the oil, will have to a couple more times if I can get it running

Was the gas flooding from the bowl vent or internally in the throat of the carburetor?

Did you disconnect the electric fuel pump during this test as I recommended in post #26?

Bert

I did disconnect the fuel pump but I have no way of seeing where the flooding is coming from, I don't have any one to help crank and watch, I might could set up a camera, I'll be fiddling with it again today

I have held up a mirror to see the bowl vent while actuating the starter under the hood. Be careful doing this because the battery terminals are right there.

Bert

I just disconnected the fuel pump watched the bowl vent and it floods internally, nothing came out of the bowl vent, I unplugged the pump electrically and removed the fuel line from the carb, base gasket is wet with fuel also

The next step will be to confirm that the Pump Plunger "cup seal" is actually sealing. (I have seen new rebuild kits that had cup seals that didn't function properly) The seal should be a firm to snug fit in the bore, remembering that vacuum will need to be able to pull this plunger / seal assembly up in the bore.

What material are the cup seals made of, in your carburetors? Viton / Rubber or Leather? If leather you can bring it back to life by soaking it in Neatsfoot Oil or a light 3 in 1 type of oil. NOT SOLVENT! If it is the Viton /rubber type you will need to buy a new one.

If this seal has shrunk it will allow gas to be drawn up the pump plunger "vacuum circuit", this is directly routed to through the governor riser block to the manifold. I think this is why you are seeing the wet base gasket. This may be why it didn't leak while you had the assembly removed from the manifold for the one test.

Bert

Very INTERESTED in seeing how this story ends. Sounds like Bert maybe on to something.

I finally got some time to fiddle around a little more today. My cup seals are purple so I know they are not leather, the carburetor i rebuilt was very snug, it takes a little pressure to pull the top off, however there was a small piece of the bottom of the seal that got a little messed up when i first installed it, The carburetor VPW rebuilt for me is not nearly as snug, but is still snug, what are the chances that i have 2 bad cup seals, both carb kit and carb are less than 3 weeks old. I do have another cup seal that is leather that came in the rebuild kit for the E7T2 carb, i dont' suppose i could try to use that one just for testing? I also finally got the stock fuel pump rebuilt, now i need to order new rubber lines and reinstall it. Thanks again bert for all the help. I talked to a local mechanic the other day and he was kinda wishy washy and said if i left it with him for a couple of months he should be able to figure it out. No computer so most people around here don't know where to start!

My brain housing group keeps dwelling on the question, two bad carbs what are the odds. Be interesting to see how the new fuel pump changes the picture once you get it hooked up.

Bert described the same issue i had with my M43B1...but it had several issues all at one time to deal with.

My accelerator cup was leather and it took 2 to get the sealing correct. For some reason trying to recall here....i keep thinking there was an internal steel check ball in one of the circuits as well?????

I also has the fuel pump elec type....I disconnected that and went to a hanging bottle to muddle through it. I had my pressure very low in the end.

It is amazing how working on carburetors is becoming a lost art form with newer mechanics. If it doesn't throw a code to their scan tool, you might as well forget it.

I wish that I lived closer to you because we could of figured this out in a couple of hours on the bench.
I feel confident that the fuel pump is not the root cause of this flooding, more likely a bad cup or parts not installed properly.

Next step:
There is an intake check ball under the pump plunger that you could check to make sure that it is in the correct position and that hasn't migrated into the over to the discharge side of the passage. (should be in the port that is fed from the bowl)

There is also a check ball in the discharge passage under the discharge passage plug. I have seen people install the spring on this upside down but this results in excessive gas being dumped out through the pump jet into the carburetor throat. (The spring should be installed with the small end down against the check ball)

Bert

I will check both tomorrow, I'm not opposed to sending you my carburetor and letting you look it over! I'd pay well! It's just hard for me to conceive that I'm having the same trouble with 2 different carbs rebuilt by 2 different people, it's just killing me that I can't figure out one of the simplest motors I have come across, diesels are much easier to me. Thanks again for taking your time to help try to figure this out