The Stovebolt Site Forums The Shop Area Engine Shop engine stumbles and dies on acceleration ...

Per the subject, the '49 splasher 235 will accelerate fine until third gear, sometimes 4th. Then, it will stumble and even with pumping of the accelerator, it will stumble and will not rev, just stumble. Sometimes it will just die. After sitting or low idle for a minute, it will rev again and off we go ... until third gear.

This is happening subsequent to the installation of a fresh, professionally rebuilt Carter W-1 carb, a brand new fuel pump, new rubber fuel lines and a new fuel filter. I have drained the tank (to check for crud -- nothing but clean gas)

Ideas?

What happens if you choke it? I'd suggest doing a fuel pump capacity test, where the fuel line at the carb is disconnected and put into a catch container. 30 seconds at idle speed should produce ay least a pint of fuel. If not, start looking for line restrictions or a bad (even if it is new) fuel pump. If you get good volume- - - -the problem is in the carburetor.
Jerry

Edit: a low float level will produce those symptoms as the power valve opens and the carb starts drawing the max fuel flow in 3rd. or 4th. gear and empties the float bowl.

Have you tried it with again with fresh gas in the tank?

Too lean mixture in your rebuilt carb?

I'm just chiming in so the Bossman doesn't sit 30 minutes without an answer...

Brad

Float level sounds like a good start. Easy way to test is simply rev the motor while looking down the throat of the carb with an LED flashlight (LEDs make the gas much easier to see than using incandescent light). Hold the revs for a few minutes and see if you can empty the carb fuel bowl.

Also test the accelerator pump circuit. Take off the air cleaner, shine the light down the carb and actuate the accelerator from idle to full open. You should see a nice, solid stream of fuel.

"The usual complaint when the accelerating pump circuit goes bad or becomes defective, is a noticeable "flat spot" when trying to start from a complete standstill or a hesitation on acceleration. A quick check can be made as follows: With the engine stopped, remove the air filter. Look down inside throat of the carburetor. Open throttle by hand, slowly at first and then quickly. Watch for stream of gas coming from pump jet. It should be a steady full stream from the start to finish of throttle travel. If the stream of gas is not full and steady, remove the carburetor and completely check pump circuit."


"professionally rebuilt" does not mean as much as it used to.

John,check the rubber fuel line from the pump to the tank it might be closing up.


Pete

Rig yourself up a fuel pressure gage where you can see it while driving. If the pressure disappears just before you hit 3rd then you'll know the fuel pump isn't keeping up with the engine. If the pressure stays up then you'll know it is in the carburetor.

Before guessing at the problem, I would like to state that I am NOT the professional that rebuilt the carb; so have no axe to grind.

The carb doesn't care if the truck is in first gear or fourth gear. Sounds like the carb is working if there is fuel in the carb.

There are two possible conditions (that I can think of) in the carb that could cause the problem:

(1) sticking float
(2) use of the "2-ball" fuel valve

The fact that the carb is able to catch up with idle probably eliminates (1). As to (2), I thought the company making those things was out of business. Hopefully, your professional did not have one of these valves on the shelf and used it. I would suggest asking.

So basically, the symptoms point to the fuel delivery system. Possibilities in the fuel delivery system:

(1) new fuel pump of off-shore manufacture, even if in a Delco box.
(2) clogged fuel filter
(3) rubber fuel line
(4) cracked fitting in fuel line
(5) missing or partially clogged tank vent

Discussing:

(1) have personally had virtually nothing but trouble with new auto parts for older cars coming from the other side of the world. (Opinion) rebuilding the original is better.

(2) I read that you changed the fuel filter. Same answer as above.

(3) You stated new rubber fuel line, but not how much. The only rubber should be a "vibration" joint from the frame to the fuel pump. Too much rubber can collapse from vacuum.

(4) A cracked or loose fitting in the fuel line before the pump won't leak, as it is not under pressure, but can suck air under vacuum, thus reducing the output of the pump.

(5) A missing or partially clogged tank vent will not allow air to enter the fuel tank as fuel is pulled from the tank, eventually creating a "vacuum lock" on the tank. Do not know one way or the other on your truck, but many older vehicles had the tank vent as a hole in the center of the fuel tank cap. New production caps, as a rule, do not have this hole.

So where to start?

First, a call to the rebuilder to see what type of fuel valve was used. If the two-ball valve was not used, then just try another new fuel filter (cheap, and fairly easy).

Next, as Jerry suggested, a fuel pump capacity test.

Next, with the aide of a helper to listen for escaping air, try blowing low pressure air from the suction side of the pump back into the tank to locate the tank valve or a possible leak in the fuel line.

Jon.

Update -- Put the carb I borrowed from Mike Roache back on and it runs fine. So I will trouble shoot the carb as described above.

Thanks for the inputs!

John