Too much vacuum?
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Tuned
Joined: May 2004
Posts: 334
Likes: 4
Too much vacuum?
1966 F100 240 six cylinder one barrel carb. This is to the point of rediculous. I keep running out of fuel. Is it possible to have too much vacuum, and the fuel is being pulled out of the carb faster than it refills? The truck runs like a top, but will just run out of gas. Lines are new, pump is new, filter is new, carb is rebuilt, but swapped carb with same results. Compression is 115 and vacuum is 19.5. Vacuum seems high vs compression, but I am grasping at straws now. Fuel pressure is good, and if I loosen the line at the carb after it quits fuel pressure is evident. I am really at my wits end. This should not be a difficult problem to solve. Please help!
Tommy
I do have gas in the tank
Tommy
I do have gas in the tank
Last edited by tommyleea; May 19, 2008 at 07:22 AM. Reason: add comments
Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
Having 19.5 in/Hg of vacuum is good. If it was lower then you'd have an issue or a big cam with lots of overlap. You could also have a hole in the gas tank pickup tube, junk clogging the end of the pickup tube, a hose clamp not tightened all the way, or the non vented gas cap.
Double check your hose clamps or fittings to make sure they are tight.
Try running the engine without the gas cap on. If it keeps dieing on you then continue down the list.
I had to replace the pickup line inside my tank. That was after pulling hair and a lot of curse words flying out when it kept doing the same thing. It ran like a champ until the gas level dropped below the top of the tank. I had a pin hole right where the pickup exits the tank. It would run all day long idling but when I used more fuel then the line could support it would die on me.
You could also have a large rust flake plugging the pickup line then floating away after the suction is gone. To see if it is junk clogging the pickup, remove the fuel sending unit and watch when the engine dies to see if something is blocking it.
Double check your hose clamps or fittings to make sure they are tight.
Try running the engine without the gas cap on. If it keeps dieing on you then continue down the list.
I had to replace the pickup line inside my tank. That was after pulling hair and a lot of curse words flying out when it kept doing the same thing. It ran like a champ until the gas level dropped below the top of the tank. I had a pin hole right where the pickup exits the tank. It would run all day long idling but when I used more fuel then the line could support it would die on me.
You could also have a large rust flake plugging the pickup line then floating away after the suction is gone. To see if it is junk clogging the pickup, remove the fuel sending unit and watch when the engine dies to see if something is blocking it.
Posting Guru
Joined: Dec 2000
Posts: 1,793
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From: San Diego CA
You say "running out of gas" please elaborate is the carb not getting fuel or the tank emptying. Does it run fine until you put a load on it. Runs good for a while and just quits. Runs out at 1/2 tank all the time. Don't spare any details. So far if it is a fuel problem and not ignition, it could be... not picking up fuel, air leaking into the fuel line, a defective fuel pump, clogged fuel line, vapor locking, very low float level, a gas theif in the neighborhood.
Posting Guru
Joined: Dec 2000
Posts: 1,793
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From: San Diego CA
After rereading you post I would wonder if it wasn't an ignition problem. If it's getting fuel into the carb and two different carbs had the same result then a fuel problem would not be likely. What has to happen to make it restart.
Posting Guru
Joined: Jul 2003
Posts: 1,398
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From: Davenport, IA
There should be no way to suck more fuel than your pump can deliver unless something is still clogged. You do have a vented gas cap, right? Could be something like the coil the coil failing when it gets hot, but I would think something like that would take a while before you could restart.
If you can restart after cranking a bit, I would guess it's still fuel delivery. Is your float set correctly?
Just throwing out some thoughts...
If you can restart after cranking a bit, I would guess it's still fuel delivery. Is your float set correctly?
Just throwing out some thoughts...
Thread Starter
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Tuned
Joined: May 2004
Posts: 334
Likes: 4
OK guys, this isn't my daily driver, and I have been tinkering with several problems for the past year on and off. The fuel issue is the lastest. After installing my old carb again, the symtoms are a little different. The idle is unstable, but if I adjust the idle up it will keep running. I did drive it down the road, and it didn't cut out on me. I disassembled the new carb (remaned) to check it out. It looks like the float assembly is binding up. Looks like a wishbone. I mean it is tight. I took the top off the carb, and cranked up the engine, and had to physically push the float assembly down to open the needle and let fuel flow in. I may be dreaming, but I think the float would stick in the up position, and the engine would use up what is in the bowl, and then quit. I squeezed the floats together so they would clear the walls of the carb, and it seems to move freely now. I also see that the rubber piece on the accel pump is missing some of its seal area. I am going to see if I can return the carb today. If this doesn't fix it, I guess I will pull the tank out next. Thanks for all the ideas. More than one set of eyes always helps. Thanks again.
Tommy
Tommy
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Cargo Master
Joined: Jul 2006
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From: Concord, CA
After what you say about re-manufactured carbs I really wonder if they are worth the money. Would seem that either you rebuild it yourself or have someone with a known reputation do it. All 4 of my cars running carbs have had them rebuilt by Pony Carbs. A little expensive, depending on type, but well worth it in my opinion. They come back looking like works of art and run like a swiss watch with never an issue for me in the 2100, 4100 and 4300 versions. I know one guy who thinks the owner is full of it but that is probably because that guy is a Holley fan and Jon, of Pony Carbs, thinks the Autolites are still the best.
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Postmaster
Joined: Nov 2001
Posts: 3,351
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From: Escondido, CA
The other night I pulled a reman carb from Holley off the shelf where I work and I had to send it back. I was debating on buying it for myself to replace the carb on the wifes Fairlane. The threads for the choke port were cross threaded and cracked but it was reanodized. How's that for a quality job from a known name brand. Afterwards we all talked about randomly pulling remain parts and spot checking them for quality when time permits.
