The Stovebolt Site Forums The Shop Area Engine Shop Gasping stumble out of idle

Hey everyone. Well I've searched and read and reread everything I can find, and still having problems.
Okay so here is the situation: I've got a 54' with a 235 and a rochester b, the engine idles perfectly, but when I step on the accelerator it gasps, stumbles, and (if i don't let off the pedal)dies. I found that I had a small pinhole in my vac advance, so I replaced it (that helped alittle. The carb has a brand new rebuild kit in it including the accelerator pump. there are no vac leaks around the manifolds and pluging the vac feeder line to the wiper motor has no effect.
The only thing that fixes the problem is if I place a piece of cardboard about 2/3-3/4 over the carb throat (choke without upping the throttle).
Any help anyone can offer would be great.
thanks

There is a small ball in the bottom of the accelerator pump. This closes when the pump is activated and forces gas under pressure into the carb throtle body. Look down the carb and press the accelerator to insure you have a good gas flow, if not this ball is missing and your not pumping enough gas to the manifold. This ball is overlooked a lot and was the cause of my problem, which sounded kinda like yours. Hope it works for you. Keep us informed..

The symptom is classic for the accelerator pump. Ditto Beaver on working the throttle and checking for a good solid stream of gas from the accelerator pump. If it's anything less than a solid stream from the beginning to the end of the throttle movement it's the pump.

Thanks for the suggestions guys. I just grabbed a flashlight and went out and checked. I've got a strong stream for the whole of the throttle travel. Its a little dark for taking the carb apart, but I'll check on the little ball in the a.m.
Thanks again

In 52 the model "B" carb was revised and the ball in the bottom of the accelerator pump well was eliminated along with the screen and passage for the pump. Look down the carb throat at the airhorn cross bar. If there are only two small holes in the center of the cross bar you have the revised carb. The carb should be mounted to the manifold using either a double thickness flange gasket or an insulator, but not both. There is a vacuum port on the bottom of the carb for the power jet. Make sure that port is not blocked off by the gasket. If it is you have the wrong gasket. If you use the insulator instead make sure it not upside down. The notches should be facing up.

Thanks Jim,
Right now I've got both the insulator and gasket. altho I am using a gasket that accommodates the vacuum port. In the morning I'll give it a go without the gasket.

UPDATE:
well I got up and pulled the carb apart, , and as Jim suggested there is no ball or screen (and no place for one). I tried removing the gasket, but didn't change anything. Sooo... I'm stumped.
A little more info about the problem: if I press the throttle slowly there isn't a problem until the rpms get fairly high (no tach, no idea exactly how high). as for the accelerator pump; its new, and the cylinder it fits into shows no signs of wear.
Once again thank you for you thoughts and help.
-Owen

float height?

the float drop was a little high, fixed it but it didn't help the problem (now at: 1 9/32 & 1 3/4).

Kermit54,

I'll take a guess. Once the throttle comes off idle, you are utilizing a different circuit of the carburetor. If you VERY slowly advance the throttle to negate any accelerate pump function, and the engine still gasps and stumbles, I think the accelerator pump isn't the issue.

It sounds like you have a passageway or metering jet plugged. I would try two procedures before I removed the carburetor again for another inspection.

I would cross two plug wires and start the engine. This will cause a pop back through the carburetor that will sometimes clear a plugged artery.

A second shade tree procedure is to get the engine running as fast as you can, however you can, and clamp the palm of your hand over the air horn choking the engine until it stops. When you do this, make sure the throttle is wide open until it dies. This procedure will sometimes help clear any junk from the carburetor.

These are easy to do, won't cause ill affects, and have worked for this "okie mechanic" in the past. Keep us posted.

Stuart

The only other thing I can think of is maybe you have a vacuum leak at the throttle body shaft. When I rebuilt my carberator (also a model "B") I noticed a lot of slop where the shaft went thru the throttle body. I took it to a machine shop and had them put new bushings in to tighten it up.

Try advancing the timing about ten more degrees and see if the stumble goes away, worked for me. If the engine kicks back against the starter, you have it advanced too far. You are not going to hurt it by trying this unless you get a persistent ping.

Hey Jim, I’m always interested in learning more about the Rochester ‘B’ carbs and their evolution. Where did you find that information about the revisions in 1952 and do you think I can get a copy of it?

Denny Graham
Sandwich, IL

-Atomarc tried both techniques (think I'm gunna have a hickey on my hand) they seemed to help. easier to get around the "zone of death". guess I'll pull the carb and get medieval on it with the cleaner and compressed air.

-Jim, how would I check the throttle body for leaks (starter fluid?)?

-Baldy, I killed my battery with all this on and off business. So I'll give the advance a try in an hour or so.
Thanks to all of you, I think we're making progress!

Well Baldy I tried the advancing trick still no go.
Have I mentioned that any load on the engine and its twice as bad (can't even go two feet).

hmmm. . . this thing got a manual choke ? she stumble hot or cold or both. . . Before i put a Carb kit ( as sugested MR carbking) in my GMC it would do about tha same thing i found i had to run full for about the first half min it run then shut the choke all 1/4 of the way it would run fine shut all thway ideled fine but would die when i tryed to go. . . :confused:

Denny,

Carburetor design changes for 1953

Okay everyone, problem resolved!!! after frankinsteining my current carb with an ancient one I had arround I made it to the gas station and back without incident. It appears that the issue was the main metering valve. I say this because when I first put the hybrid carb back on the truck I still had the problem, but after swaping the mmv, evereything ran great!! Thank you all for all your ideas and suggestions, I don't know what I'd do without stovebolt.com.
P.S. I'm still saving up for a carter yf thow