My carb needs some help

boggerted · #1 (**permalink**) 04-14-2008, 08:41 PM

On my 84 F250 351w 2bl carb, if you are driving at low rpms, then punch the throttle, it bogs down and starts popping through the carb. If you let up on the gas, it stops and accelerates fine. Ive rebuilt the carb and it runs fine otherwise.

Franklin2 · #2 (**permalink**) 04-14-2008, 09:12 PM

Take the aircleaner off, and with the engine off, look down the carb throat, and just barely push the throttle back. Did you get anything out of the squirters for the accel pump? You can try again, and while watching the squirters, and making a mental note of how you are pushing on the throttle, push it back all the way. The streams of gas should start right away, and be very strong, especially since you just rebuilt it.

You can't have any delay in the fuel squirting down the carb throat, or you will get a bog and the popping. The popping is the engine leaning out. Don't experiment too much with out starting the engine, or you will flood it.

If that all looks good, then the timing could be way off, and it can have this symptom, but if it did not do it before, and after the carb was rebuilt it does it, then I would suspect you may have lost the check ball out of the pump circuit, and forgot to put it back in.

boggerted · #3 (**permalink**) 05-28-2008, 09:49 PM

Do you have a diagram of the springs inside the accelerator pump? Mine uses the diaphragm with the spring permanently attached if that helps at all, because Im not seeing any fuel squirting in, and the diaphragm is new.

Franklin2 · #4 (**permalink**) 05-28-2008, 10:13 PM

Here's a exploded view.
Carburetor Factory - American Motors 2100 Exploded View

More than likely you are missing #41, or #33 or #34.

boggerted · #5 (**permalink**) 05-28-2008, 10:45 PM

I know 33 and 34 are there because I had to redo it after forgetting the check ball the first time. The rubber part (41) was replaced, but it doesnt seem to fit tight on the metal, it flaps around loosely. Is that normal?

85lebaront2 · #6 (**permalink**) 05-28-2008, 11:11 PM

No, you have to pull it through until the "bump" comes through the hole.

Piffery1 · #7 (**permalink**) 06-01-2008, 01:31 PM

The elastomer valve shank should pass through the hole in the center of the pump chamber. You may have to apply a little grease to get it to pass through the hole and seat properly.

boggerted · #8 (**permalink**) 06-01-2008, 03:09 PM

It did pull through past the bump, it just doesnt seal right. I think though that the metering rods not opening is also causing me problems.

Piffery1 · #9 (**permalink**) 06-01-2008, 03:27 PM

Sounds like you may have the wrong size elastomer valve. Do you still have the old one to compare? I think there may be two different (at least) sizes. The metering rods are actuated by a removable cam on the throttle shaft; is it still properly in place?

boggerted · #10 (**permalink**) 06-01-2008, 06:43 PM

thats the problem, that cam isnt a tight fit on the shaft due to wear, so it takes a while to engage, and sometimes, it wont engage at all, it just spins around.

Piffery1 · #11 (**permalink**) 06-01-2008, 09:55 PM

I think your best bet is to get a rebuilt. Or, find a cheap used one and get the parts you need off it. I sent you a PM with a link to one on ebay that looks pretty close to what you've got.

boggerted · #12 (**permalink**) 06-02-2008, 06:26 AM

Thanks piffery for the link. I think im going to get a new holley 4412 as a replacement

Piffery1 · #13 (**permalink**) 06-02-2008, 04:50 PM

Ooooh, I'd hate to spend that much money for a new carb! Can you crimp or wedge the cam to fit tightly on the throttle shaft?