The Stovebolt Site Forums The Shop Area Engine Shop What the heck is going on with my carb?!?!?!?

My truck has been bogging out under acceleration, it will rev, but the power isn't there and it seems to only happen when the peddle is pushed at any rate faster than very slowly. I figured a rebuild would be in order, so finished with it, same problem. It was a total rebuild with new jets and all. The truck is a 1951 4400 with a low pressure 235 and a rochester carb. Runs and sounds great otherwise. ANY ideas?
Thanks in advance

Lunchbox...look for the thread titled, Climbing Hills here in the Engine Shop forum....should answer you question !!!

Is the accelerator pump shooting fuel when you open the throttle?
The pump is the first thing to check and or repair, next thing to check is fuel flow. Filters, lines, pump, fuel tank, all can cause delivery problems. Work you way back to the tank, checking each piece. Run the engine with out the line hooked to the carb, the fuel should fill a small bucket pretty fast, ( it should idle long enough for this test on the fuel in the float bowl). If you get a weak stream or very little fuel, your problem is the pump or the tank outlet. Pull the line at the tank and see how fast or slow the fuel drains. Is the fuel cap vented? does the tank make a sucking noisy when you pull the cap? Any number of these can cause slow fuel flow.

Joe

Just a guess check the vacuum advance.

Marv.

Vac advance is working fine. Just checked the accelerator pump. can't see any fuel squirting when I pump it... although I just rebuilt the carb and installed a NEW accelerator pump. Not sure what is going on with it. I made sure all passages were clean and clear of debris when I rebuilt it friday. Guess i'll pull it off again and see what happens.

Joe,

Carbs can be difficult beasts - they do many things, both at once and at different times, and I don't think it's unusual to have to go through it twice or three times before you get it where it's supposed to be.

I agree with Joe H - test the fuel flow first, because without good flow, the best carb won't work right. So get that out of the equation first.

You should definitely get a squirt when you goose the throttle (looking down the throat of the carb, air cleaner off, engine not running). And the problem you describe DOES sound like the accelerator pump failing.

But check that fuel flow first. Pump may not work because there's not enough fuel in the bowl!

-Michael

you know what? that makes alot of sense actually. Lately while driving it has been low on power, and on the highway it tended to sputter a bit unless i floored it and then backed off. Tested the flow, very little is actually flowing to the carb. New fuel filter didn't help. So I would have to imagine that its the pump? Thanks for the help so far guys

Check the fuel pump before replacing it. The 60-year old tank and feed line may have become clogged with sediment. The 51 is a gravity feed to the pump, so it should gush out if you disconnect the hard line at the pump. I had a 53 3100 that the feed line was clogged enough that the carb bowl would fill at idle, but it couldn't keep up with the fuel demand while driving. It would start and idle fine. Then after being driven about 1/2 mile it would quit.
It would restart and idle okay, then die again just as I got back to the driveway at home.

regards,
Leon

Crud lodged in the valve at the bottom of the tank can create these symptoms.

Mine bogs out like that too, unless it's been running for quite some time. EVERYTHING fuel related on it has been replaced with brand new, so I'm assuming that's just the way these old engines are. Kinda [censored] me off though when a Dodge truck close to the same age as mine (it was a 66, mine's a 61) started up beside me, revved quick (nice Vroom Vroom, not sputter, then vroom like mine) and took off rather fast. He had a 225 slant six in it, I chatted with him for a while. Were these Chevy 235s with the rochester really that finnicky? It runs good but I feel that it could still run better.

I had the same problem. Mine was severe enough that the engine would actually stall out.
I fixed mine by setting the timing with a vacuum guage attached to the manifold while keeping the idle speed and mixture in specs.

Jim

Alright, update time. A new pump gave me slightly better performance, took the carb apart again and noticed I installed the T that holds the accel pump spring and ball in a way that partially covered the fuel port! Doh! Fixed that, reassembled, fired up and ran great! Thanks for the help everyone!

When you say you replaced everything in the fuel system. Does that mean replaced the filler tube too? I replaced everything but that and I still got a couple of little chunks of rust stuck in the fuel pump. The filler tube was in very good shape, other that a slight bit of rust which I didn't even think about until it started running very very bad. I had the same thing happen on my mustang.

Brokenhead, yes, everything including the filler tube. The carburetor was the first thing to be replaced however. It was run several times with a new carb and old everything else, so maybe I messed up my new carb. May rebuild it and see what happens.
The carburetor has a fairly loud sucking noise, especially under load. I can even hear it very well from inside the cab, windows closed.

Alright gang, update. Drove Cecil to work and back the other day, all was well. Yesterday I went out to start it, and noticed that there is a problem when goosing the throttle again. hmm me says. Turn it off, take off the filter and give the gas a pull, nice strong squirt out of the acceleration pump port. Fire it back up, same problem. Take a look in the carb with the engine runing, give the throttle a pull, and notice no squirt. The only thing I can figure is that my bowl isn't filling up enough, meaning my float level is wrong? I thought I had it dead on, and why would it be a sudden development? Just as a recap, Carb = fresh rebuild, Fuel pump = New, Fuel filter = new, Fuel lines = all clear. Any ideas? Also, checked fuel flow to make sure the pump wasn't faulty, or didn't "wear out" in the week it has been on. All was fine.