a loud pop from carburetor

[krumpelsaurusrex]

After a few days of sitting I went out and attempted to start the truck. It would start for a second then stall. Even with my foot all the way on the gas, it would stall. the only way to get it to start is to keep foot on the gas and turn the key for a few seconds, after 5 or 6 chugs it starts then acts normal. If I turn it off it will turn right over again. So I am assuming it's the power valve?

[george worley]

One way you can check for a blown power valve is to turn both idle mixture screws in [that makes it lean] if the engine dies the power valve is usually not blown, but if it runs better it it it is most likely blown. I have used this method on Holley carbs with good success. I believe it would work on Autolite and Motorcraft carbs as well. Older model Holley carbs were bad about blowing power valves. If your valve is blowed you can get a new "blow proof " power valve from Holley.

[krumpelsaurusrex]

Well I took it for a drive to dinner, where I'm at now. When on the fwy in 4 th gear it started to surge and jerk. Based on what had been described before in this thread, Any ideas to narrow it down a bit? According to my father in law who drove it home frome previous owners house, it did not surge on him.
Trying to get it ready for 4 th!

[fordman]

here are possible guesses on the generic situation of the description. in general a loud pop from the carb. could be a - backfire? incorrect timing ? a slip of the timing chain or distributor gear on the bottom of the dist shaft? maybe a bad or wet dist cap. and or crossfiring spark plug wires. can create the same running issue. a bad or clogged fuel pump or line. the duraspark system on hte later trucks can also give a running condition such as a surging or bucking when the duraspark box is trying to get hot and go out on those systems. but they wont always give those signs. sometimes they just quit dead too. these trucks can aslo get things dropped down into the gas tanks that will temporarily or completely clog the fuel line inside of the tank. until fuel line suction has had a change to decrease and let fuel past it or the blockage fall of of the suction for a few seconds. just long enough to let it get enough gas to let it keep running. this is all just some guessing on this type of symptom. things that sound similar to how you describe it.

[BobbyFord]

Generally, a backfire from the carb indicates an intake valve open at the time of spark. It's very common on FE's that sit for a while to develop sludge/gunk on the valve guides, causing the valve to hang up in the guide. Sometimes, depending on where in the guide the valve hangs up, a bent pushrod can be the result. Sometimes the valve only hangs up for a second in the full open position and the pushrod does not get bent. If the pushrod was bent, you'd be experiencing a cylinder misfiring accompanied by valvetrain tick. If you suspect sludge build up, I'd run a high detergent oil with maybe a quart of ATF (4 qts. oil and 1 qt. ATF) run it for 500 miles, change the oil and go from there.

[krumpelsaurusrex]

here are possible guesses on the generic situation of the description. in general a loud pop from the carb. could be a - backfire? incorrect timing ? a slip of the timing chain or distributor gear on the bottom of the dist shaft? maybe a bad or wet dist cap. and or crossfiring spark plug wires. can create the same running issue. a bad or clogged fuel pump or line. the duraspark system on hte later trucks can also give a running condition such as a surging or bucking when the duraspark box is trying to get hot and go out on those systems. but they wont always give those signs. sometimes they just quit dead too. these trucks can aslo get things dropped down into the gas tanks that will temporarily or completely clog the fuel line inside of the tank. until fuel line suction has had a change to decrease and let fuel past it or the blockage fall of of the suction for a few seconds. just long enough to let it get enough gas to let it keep running. this is all just some guessing on this type of symptom. things that sound similar to how you describe it.

One way you can check for a blown power valve is to turn both idle mixture screws in [that makes it lean] if the engine dies the power valve is usually not blown, but if it runs better it it it is most likely blown. I have used this method on Holley carbs with good success. I believe it would work on Autolite and Motorcraft carbs as well. Older model Holley carbs were bad about blowing power valves. If your valve is blowed you can get a new "blow proof " power valve from Holley.

Thanks again for the info. It's gotta be something with the carb or fuel delivery. To start the engine pedal needs to be to the floor. On the 4th we loaded her up and took her out to the speedway for a day of tail gaiting and fireworks. After a few min on the fwy it started bucking and acting like it wasn't getting enough gas. I tried letting of the gas and also pumping it, nothing helped and it stalled. I pulled over for a few min. It had a hard time starting until I pumped the gas, then we were good. If I took side streets he runs like a champ. Just fwy in 4th it surges and stalls. Needless to say I signed up for AAA at the speedway when I got there!

On my way back I drove it to a family gathering and a few said it smelled a bit "rich" when I drove by. A good amount of gas fumes. So I'll try the mixture settings that george mentioned, and also check for obvious fuel blocks as fordman says.

[NUTNDUN]

I am guessing the idle mixture needs to be set but first the timing should be checked. The surging on the highway sounds like a lean condition. Have you replaced the fuel filter? Another thing that fits the bill would be a vacuum leak.

[VirginiaCityFord]

Change the oil and filter and put a can of Marvel Mystery Oil with the new oil. Run it a week and change oil and filter again. Marvel Myatery oil cleans the varnish out of the lifters and helps clesn the sludge out of the engine.

You can also do the same thing with ATF, works exactly the same