The Stovebolt Site Forums The Shop Area Engine Shop 55' Rochester carb runs 45 sec, the dies

I am about to disassemble a new rebuilt carb, as I have already disassembled my head on this. The carb runs good to perfect, (only slightly weak), then it acts like no fuel is getting to it, even though I can see it getting pumped in through clear filter.
Upon vigorous revving, it's smooth until some backfiring happens., sometimes revving rescues the operation and sometimes it is not enough and it dies.
The gas tank is clean, the fuel line is clean, its fuel pump is brand new, things are very tight. I tend to think a sand particle may have gotten into the carb. I know I need a mechanic, I feel like I am way beyond my p-principle, but I also know that this cannot be that hard, not with all the info and great minds out there.
I certainly could use some suggestions before I screw up the carb by taking it apart. It seems to be what I do. PS This is manual choke Roch. I think its a bb.

Do you have access to some form of remote gas tank such as from an outboard motor that you can put a known pressure supply of gas to the carb by manually pumping the bulb?

You don't say if it does this sitting in driveway or just when driving. If in driveway then homer's idea will be easy. Hose from a gas can to pump inlet as a test. Can on the ground, stick hose down in thru mouth of red plastic 1 or 2 gal $9 gas container, no bulb necessary (bypasses all your system up to pump). This will isolate it a little.
causes:
1. Vacuum leak somewhere
2. Float level
3. Internal carb dirt
4. Gas cap not venting
5. Plugged filter somewhere
6. Bad new pump
and a bunch of other stuff, but first:
1. look down carb throat and see if gas is squirting into venturi. After is dies.
2. Seeing gas in the clear filter is not much help. Maybe it's flowing and maybe an optical conclusion.
3. Sounds like someone has been working on it recently (new pump,etc). Don't know history of this event.
4. Don't tear into carb until you hear from others and do various other easy tests.

One step at a time. As in: Check for vacuum leaks and observe squirt.

Does it idle forever but no acceleration? Won't idle? Won't start right back up? Info, info, info

My vote is #4

Sounds like a timing issue to me, mainly that the timing needs to be advanced.

Unless you have checked the fuel pump volume by pumping gas into a container with the engine idling, you can't be sure you've got fuel flow. You need at least a pint in 30 seconds at idle. I've recommended this hundreds of times, and most people ignore me- - - -don't know why I waste the keystrokes!
Jerry

Jerry, appreciate your info anytime. I've learned allot from you.
I've done the pump/container test many times and I know you have.
When many read that they think it's a dangerous, fire happy, messy, smelly, eye splashing job. Which, of course, it is.

I understand how you can disconnect the line, run the starter, and pump into a container to check volume.

However, doing this with the engine idling has me a bit confused. Run the engine on a plastic gas can while the pump is running into a container?

I would check the timing as Bill suggested above and would also pull a couple of spark plugs to look for overly rich or lean fuel condition.

DON'T TEAR DOWN THAT CARB JUST YET!! I'm with Jerry on this one! Sounds like a fuel delivery problem to me. That "NEW" fuel pump may be BAD. Won't be the first time I've gotten "BAD" NEW parts. Disconnect the fuel line at the fitting going to the carb and put a threaded fitting with a barb into the fuel pump. Attach a rubber fuel line to the barb and out to a container. Disconnect the coil to the distributor. Have someone crank the engine and watch the fuel volume and pressure. That is where I would start.

Tim

To whom it may concern:
IF YOU ARE POSITIVE YOU ARE NOT JUST OUT OF GAS!,

1. Take off gas cap and test motor. Still stalls? Then:
2. Check squirt in throat of carb, after dying. Not running. Report.
3. Check flow. Disconnect at carb, disconnect coil so it won't start, crank motor, observe how much volume and how strong the pulse is...into a container. I think Jerry did not mean to say "at idle". If Jerry did mean at idle, I don't do it that way.
4. If above test shows good, report here and move to next step. If that test shows insufficient flow, hook hose from can to pump inlet and observe outlet again. still insufficient? bad pump. If flow is good after hose from can, there is an upstream block.
No. 2, 3 & 4 is with motor not running, just cranking.

(P.S. JW51, I did confuse the testing. You can run the motor with truck sitting in the driveway from a gas can sitting on the ground. With pump outlet still attached to carb. This is usually done when checking a truck you want to buy that has been sitting for years. To see if it will run without sucking in bad gas. NOT in this case. In this case it's not for running, but to isolate the upstream flow and prove it's the pump or carb or neither)

If tests show flow is good and you see squirting in throat, probably not fuel delivery.
Put all back together and
Then check vacuum for leaks, be sure there are no vac leaks.
Vacuum leaks:
1. At carb base
2. At carb spacer
3. Intake manifold gaskets
4. Any carb or manifold port, fitting or hose
5. Make sure exhaust manifold heat flapper is not stuck
6. Wiper hose leak
7. You can use gauge, carb cleaner or propane as a detector. Wait for instructions on this if you don't know.

All good?:
Then check timing and begin thinking spark problem/loose ignition wire somewhere. Bad battery or charging. Choke closing.



Some of the advisors have a different sequence of troubleshooting and different ideas of what is wrong. This is normal and healthy. Using a different way of figuring it out is OK and may be a faster track. This is just what I think I would do, without being there. The goal is the same from all of us. We go buy what a poster says, their answers to questions and a feeling we get about the issue. It's always based on good fuel/air, spark, compression. Because it runs, kind of good, then dies, but "backfires, does not seem like timing at this point. But never sure. Agree Must check sooner or later. "Backfire" is also a vacuum leak. Backfire is a very subjective word.

Hey fellers, slow down. Ole Ziptadoda has not responded back even one time yet.
You may be talking to a wall.

Carl, I thought about that too (to whom it may concern) but it's only one day sinse he posted. After all, his name is not Zippitydoda.
I guess it's good to have a lot of info for when he comes back and to build a search archive for someone else....and wanted to be clear for JW's good question which was a big safety issue.

If an engine won't idle for 30 seconds on the gas in the float chamber, even if you have to fill it through the vent tube, you've got a lot more problems than just a weak fuel pump.

The volume check is part of a 3-part test which also includes checking pump pressure and vacuum, and yes, all of them are done with the engine idling. Anyone who is unable or unwilling to do it safely needs to sell his truck and his tool box on Ebay and take up knitting as a hobby.
Jerry

I would do that but afraid I might get stuck with the needle or chafed by the yarn.

No knitting for me.
Wool makes me get the hives like I was swimming in a ball pit full of loose fiberglass insulation.
I would rather risk catching myself ablaze than that.
I do like the tip for removing the pipe from the fuel pump rather than the carb. This would eliminate buggering up the carb where the fuel line goes in (I hate when that happens), and it eliminates the potential for fuel to splash around above the potentially leaky exhaust manifold.
Carl

If you don't check the line from the pump to the carb, how do you find that microscopic rust hole that lets the gas leak partway back to the fuel pump every time the engine gets shut down? I use a piece of rubber fuel line about 2 feet long attached to the line I remove at the carb and hold my catch container away from the air horn and any possible lean backfires, hot manifolds, etc. Like I said, safety awareness and common sense are becoming a pretty uncommon trait these days.
Jerry

OK Carl, you were right. We are talking to ourselves. The poster is on my list. Good Bye.

Well, where else would we find such good folks to talk to if we don't talk to each other?
Jerry

My care center.