The flattie Won't keep running

[1940Mopar]

I've finished buttoning up the new dual intake, and have plumbed new fuel lines, including finding and purchasing 4 of the last 8 5/16 inch female inverted flare T fittings in Nashville. (if there are more out there the parts counter guys don't know what they are looking at). I've recently installed a new fuel pump that seems to be working. I've got some minor leaks still but will work those out shortly. I'm adding this bit of information in an effort to make sure that I've stated everything that might be a problem.

I've installed the new Langdon Carter/Weber Carbs and run my wires for the automatic choke and they are functioning. I've also installed a fuel pressure regulator set at the recommended 3.5 lbs/psi, and I've run the supplying fuel line into a five gallon gas can as a temporary gas tank.

Here is my problem. If I pour a tiny bit of gas to start the car up it will run off of what was poured into one carb; however it will not continue to run even though it is getting fuel. I've check whether the fuel pump is working by disconnecting the fuel line at the outlet, and it is definitely pushing gas out.

What gives? Is there a recommended carb adjustment I should do prior to running the C/W carbs? I've followed the Langdon diagram as far as blocking off vacuum lines, although I could check again to be 100% sure. Is there a vacuum line I'm forgetting? I've never worked with this type of setup and may be in over my head but wanted to make sure I'm not missing something simple before i call in the professionals. I figured my next step was to synch the carbs to make it run right but I can't get it to run long enough to be able to synch.

Could I be pushing too much fuel or not enough. I've checked the spark plugs they don't seemed fouled or anything, and like I said the car will start and run from 5 to 10 seconds like a champ, but quits after that.

[martybose]

I'm running the same carbs, and if the choke setup is working it should be running. From your description I would suspect you are not getting fuel to the carbs. Have you confirmed that fuel is reaching the carbs by disconnecting the line at the carb while cranking the motor over? I suppose that the floats level could be messed up, but since I never had to adjust mine, I would think they might be fairly close as shipped.

Marty

[1940Mopar]

I've disconnected the fuel line after the outlet to the carbs but not as close to the carbs as possible. I'll definitely check that this evening. I'm also beginning to suspect my vacuum is not connected properly, and that my fuel pump may not be correct. I was suspicious at the parts counter and even after I bolted it up. However, when I checked to see whether it was pushing gas out I stop being suspicious. Now I'm beginning to wonder whether its correct, despite the fact it is pushing gas out. It may be pushing, but not enough to get the fuel all the way up to the carbs. New pump is ordered and on the way.

I've been checking stovebolt.com to get some ideas on how to run the vacuum. Marty, do you have any pics of your setup that I could use as a reference. I had heard that it would be okay to block one port for the vacuum and run a single line from the distributor however, I think I'm gonna put a T fitting in the line and run both vacuums into the distributor.

[greg g]

to test flow and volume of fuel, disconnect the line on the carb side of the pump, direct the flow into a suitable container. Disconnect the coil wire and have and assistant crank the engine. While cranking count the fuel pulses going into the container. Stop at 12, should give you between 8 an 12 ounces of fuel in the container, if less your flow rate is low. Had I a suitable container, I could have utilized this test the other day to ascertain my problem. Hard to do by the side of the road by your self.

[1940Mopar]

to test flow and volume of fuel, disconnect the line on the carb side of the pump, direct the flow into a suitable container. Disconnect the coil wire and have and assistant crank the engine. While cranking count the fuel pulses going into the container. Stop at 12, should give you between 8 an 12 ounces of fuel in the container, if less your flow rate is low. Had I a suitable container, I could have utilized this test the other day to ascertain my problem. Hard to do by the side of the road by your self.

Thanks this is definitely helpful.

[martybose]

(SNIP)

Marty, do you have any pics of your setup that I could use as a reference. I had heard that it would be okay to block one port for the vacuum and run a single line from the distributor however, I think I'm gonna put a T fitting in the line and run both vacuums into the distributor.

No need for a picture. I disagree with some of our brethren about what vacuum signal to run; on mine, I plugged all of the carb vacuum ports and added a port into the intake plenum itself. I'm running straight manifold vacuum, and I currently have the centrifugal advance in my HEI disabled by tiewrapping the counterweights, as I was getting too much centrifugal advance at highway speeds otherwise.

Given that there is a common plenum between the carbs, if the carbs are close to being synchronized I see no reason to have to use both carbs' vacuum ports.

Marty

[greg g]

Something about this conversation is bothering me and I just had a flashback to high school auto shop class. The teacher was a chevy man and didn't have much use for much else. the test engines on stands were all chevies two 6's, 2 283's and a 348. All those chevies had their vacuum chambers connected to either the intake or the base of the carb, hence manifold vacuum (high at idle decreases with acceleration) I know my experience with my 52 plymouth and a couple dodges was that the carbs fed the vacuum pot (ported vacuum increases upon acceleration) So are chevies actually vacuum retard??? I remember there were tow vacuum sources on the old sun distributor machine. I think one said GM and the other was labled other.

Since Langdons uses gm distributers, is this where the rub comes in??? And is this why setting timing on a GM says to disconnect the vacuum, and it doesn't matter on MOPARS and others using ported vacuum. Since the vacuum sources are opposite signals they can't effect the distributor the same. But if your using a GM based Dizzy I guess that manifold vacuum works. I also recall that conventional wisdom for guys drag racing chebbies left their vacuum disconnected, and their thought was that centrifigal provided full advance through out the WOT throttle of the race.

Any converted GM guys out there that can enlighten us.

[martybose]

A while back someone posted an interesting rundown of the advance characteristics of a stock OEM flathead distributor. The interesting thing it showed was high vacuum advance and low centrifugal advance cruising at low speeds (say 30 MPH), then as the speed increased the centrifugal advance came in, then as the cruising speed exceeded around 50 MPH the vacuum advance started to decrease as the throttle was opened more, and was completely gone by around 75 MPH.

The net effect was maximum total advance at maybe 45 MPH, then decreasing total farther up.

Marty

[Lou Earle]

There can be many causes one I just encountered on a 47 I just got was rust/dust for lack of a better name- in the fuel line. Previous owner had put a fuel filter in line under the rear door area. It was clogged up with rust crud and varnish. Removed tank and had it flushed and re installed all problem's gone. I would remove fuel line from tank to fuel pump at the fuel pump and see if you have any flow- should have some. Then i would blow compressed air back thru the line back to the tank. Then see if it flows - if it does then I would clean the tank because that means you cleaned line and it will clog again.

Good Luck.

Lou

[1940Mopar]

Lou,

I'm bypassing the fuel tank altogether. I've got a can of gas that I've submerged the fuel line into. I'm getting plenty of pressure out of the pump. Just need to figure out where the supply is getting choked off.

[Lou Earle]

I missed that part. Bang on side of carbs and tops with rubber mallet or block of wood to make sure float is not stuck holding needle in closed position.

[Lou Earle]

Also I have had this problem only to discover I failed to tighten down a carb and therefore the engine could not pull gas in. Are u sure you do not have a leak around the gaskets- manifold to block cracked intake manifold? or carb to manifold?

Have someone crank the car while you cover both carbs with hands- might find you have no vacuum pull or very little - that would tell me I had a vacuum leak in the fuel supply system somewhere. Remember the fuel pump only puses the fuel to the carb- it is the engine suction that gets the fuel to the chamber to be burned

Lou