Short Running/Excessive Backfiring Problem

1

1936HotRod-TwoTon

Junior Member
I'm hoping one of you guys can help me out here. I apologize for the length of this, but I wanted to explain everything I've tried so far. I'm having some trouble with my '36 ton-and-a-half. It has a '40 Ford flathead with an Edmund's dual carb intake. We just got our carburetors back from being rebuilt, and reinstalled them yesterday. The truck starts up strong and runs for a few minutes okay, but then it starts acting weak and backfiring excessively. When it gets like this, you just have to try to give it more gas until finally it will want to die altogether. Then, if we let it sit for several minutes, it will start up strong again and run okay for a while until it just does the same thing. Obviously, we assumed there must be a vacuum leak somewhere in the gas line behind the fuel pump (we are using a freshly rebuilt '41 Ford metal bowl style fuel pump). We have a short length of flexible black fuel line from the metal line that comes from the gas tank up to the fuel pump. There is no fuel filter currently, so we don't have to worry about leaks there. After trying several different combinations and having the same results, we have a compression fitting on the inlet of the fuel pump and a compression fitting on the outlet of the metal line from the gas tank. We have used teflon paste on all the brass fittings, upstream and downstream of the pump. We cut a new fiber washer for the bolt that holds the cap of the fuel pump down (this new one fits very snug). We made sure the brass screen inside the fuel pump is on top of the cork gasket between the body and the cap. I have also looked at the length of metal line from the gas tank to the pump to see if there are any obvious leaks in it, and I see none. I sure would appreciate it if someone could give me an idea of what they think might be wrong. I'm about spent on what I can think to do. Please bear with me. I'm 22, and just getting started with this hobby. Thank you very much in advance!
 
36
Welcome to the Barn

Did you check the intake manifold top and bottom for leaks or leaking vacuum hoses?

Then I would try another condenser. any condenser, just bolt it in and try it.
Bruce

Works good
Lasts long time
 
Gas cap not venting and coil resistance/condenser (as mentioned above) are the first on my list. Heat and flow are the dynamics that change once you turn the key. Here's a stretch: Is your exhaust plugged?

Lonnie
 
I had a similar problem, and it was the distributor. The rotor was leaking sparks down to the shaft. It would run ok till it got hot then splutter, and eventually not go any further. After a while it would start up again and go for a short while. Then after cooling it would restart and go a bit further, but less and less each time. managed to limp home a few times like this.

What sort of distributor are you using?

Mart.
 
to eliminate the fuel problem, when it starts to die squirt a little gas in the carb with a squirt gun, if it still dies its not fuel, or maybe to much, when engine dies pull a couple of plugs and see if any of them are wet, if so, to much fuel or a weak coil or condensor, hook the fuel line to a gallon can, hold it higher than the carb, does the engine run ok,? if it does fuel problem if not start checking points condensor, dist cap, rotor and coil
 
Boy I went through this with the Phaeton and almost went crazy. Then about 1/2 hour with Pat Lovejoy and it was all clear. It sounds like a fuel delivery problem and maybe the float levels or movement. First thing is to check the needle and seat. Rubber needles stick and if they have the little discs in them get rid of them because they will stick both open and closed. I believe they are called Vitron. The fuel supply should be a constant 3# stream. An electric pump hidden out of the way will really help this. My '33 had a stock new fuel pump and 2x2's. Same problem you are describing and it was just running out of fuel. I used the stock pump on the engine with an electric hidden under the floor. Solved the problem and the car ran like a scalded dog. I learned all the above after trying everything I knew and then calling Pat. So credit for the fix goes to him, I'm just passing along the process. If it starts right up chances are the ignition is doing it's job.

Best of luck,

Tim
 
All: I thank you very much for your speedy response. I would have responded earlier, but right after "cmbrucew" mentioned the condenser, I immediately went out and put the old condenser from 15 years ago back on. She's feeling good now and running like a raped ape! After 15 years of not running, we just took her for quite the spin around town. Thank you all for your advice. If you are a flathead owner, this site is a must. Long live the flathead!
 
The screen in the pump is accually a hair smaller and kind of fits inside the inner diam of the bowl BUT should be under the cork gasket,Dont see how it would fit on top of the gasket. Never seen one on top of the gasket. ken ct. Most likely nothing to do with your problem seeing it was the cond. ken ct.
 
Teflon tape is not needed on your connections. It is possible that you have excess tape and the end of the tape is closing off the fuel flow. Temove the tape and remove one possible cause of your problem.
 
Ken ct: Amazingly enough, in this fuel pump, it is not possible to get the screen under the gasket. The center of the pump where the bolt attaches the cap is tapered so that the brass screen will go down only so far. Therefore, the cork gasket is forced to go under.

V12Bill: Yeah, we don't use teflon tape at all for that very reason. We have used teflon paste in any locations where the fittings leak and need to be sealed up. It works quite well.
 
1936HotRod-TwoTon said:
Ken ct: Amazingly enough, in this fuel pump, it is not possible to get the screen under the gasket. The center of the pump where the bolt attaches the cap is tapered so that the brass screen will go down only so far. Therefore, the cork gasket is forced to go under. Either ou have the wrong screen or using the wrong gasket. Ive rebuilt 100's of these pumps and never have i seen what your discribing. ken ct.:)

V12Bill: Yeah, we don't use teflon tape at all for that very reason. We have used teflon paste in any locations where the fittings leak and need to be sealed up. It works quite well.
Click to expand...
ken ct
 
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