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Mystery stall, Take 53

Mac2Night

Bronco Guru
Joined
Aug 10, 2005
Messages
2,199
After reading all of the archieved posts on similar situations I still need some help with my specific problem.

My'73 (302 with 3sp manual) starts up and runs fine (loping idle due to cam) but runs well for anywhere between 5 miles and 50 miles (problem has happened as soon as ten minutes after driving to an hour after driving) and then it starts acting like it is out of gas (or has a bad fuel pump).

Once it dies, it is hard to start again (lots of pumping needed and heavy pedal once running). Put it in 1st gear and it will run for about 20 ft and bog down again..... over and over again until I limp home. Pulled the breather off and looked to see if I got a spray of gas when I manually worked the accelerator (it gets gas).

Some factors to consider in helping me diagnois is: I replaced the points last year with a Pertronix unit in distributor; I have a slight oil leak at the rear of the manifold; it seems to run better with the breather off (not for certain though).

I know that it could be a vaccum leak at the back of the manifold (or somewhere else) or could be trash in my tank/lines or even a coil heading south or fuel pump and plan on checking all of these this weekend, BUT why would it not start until it had been driven (well) for a while and why does putting it in gear and letting out on the clutch cause it to bog once this whole mess has started?

Any other ideas would help before I jump into this over the weekend.

Thanks,
Mac
 

WyleCoyote

Bronco Guru
Joined
May 2, 2002
Messages
1,739
Oh the dreaded Vapor-lock...That happened to me on my '70 mustang. Had a metal fuel line really close to the header. Once it go hot the fuel would vaporize in the fuel line and the stop getting to the carb. Took me forever to figure that out!
 

csjr

Sr. Member
Joined
Apr 18, 2007
Messages
675
Loc.
Lighthouse Point, FL
Although you found gas pumping through the carb after getting home, you could still have some line blockage that manifests itself only while fuel is being pumped through the line. You could test this by disconnecting the inlet line to the fuel pump (assuming mechanical) and running a short line to a fuel can under the truck. Make sure if you have a filter in line between the pump and the carb that it is new. Run the engine for a while--5 min. If seems OK I would still change any other before-the-pump filters. I had a similar problem after buying a new gas tank and it was just junk in my cheapo filter. Bought a better filter and was good. Blow out the steel line with air while filter is off to make sure you don't have a chunk of rust or gunk blocking flow in the line. Check all electrical connections/wires in your ignition system. Recently I had a signal wire pop off my coil while driving and the truck totally died. Fortunately I could pull over and after looking at things for a couple of minutes I found it and fired right up and went home. Check your wire from coil to distributor for cracks. Maybe pull the carb and flush it out to make sure there isn't gunk in the float that works it's way up to close off the jets. If it's an intake vacuum issue you can spray starting fluid around the vacuum connections with the truck running. If rpm's increase then there is vacuum leak. With your description I would guess it's fuel delivery. Usually with electrical problems there's no running at all--just dead. Good luck!
 

doghauler

Full Member
Joined
Dec 7, 2006
Messages
187
Loc.
Western WA State
I vote for vapor lock too....but as a shot in the dark, I had a similar issue that you might check.
I run a stock Ford electronic distributor which has two wires going into it for the magnetic pickup. On the old one, one of the wires was broken part way through. The truck would start fine, run great, but intermittantly it would stutter and die. What was happening was the broken wire was "sometimes" making contact, but either due to heat, rough road, gremlins, etc the connection would fail. Looking at the distributor it looked fine, you could not see the break until you pushed on the wire and it the split would open, breaking the connection.....truck die.
Took me forever to find that since it was so intermittant. Fire up the engine and start wiggling wires.
Good luck. Intermittant issues are the worst!
 

Socal Tom

Bronco Guru
Joined
Feb 12, 2004
Messages
2,442
Loc.
San Diego, CA
Make sure your key switch is good. My brother had a problem, where his bronco would stall if he made a hard left turn. Turned out, that his keys would yank on the old key switch and the EB would die.
Tom
 

WyleCoyote

Bronco Guru
Joined
May 2, 2002
Messages
1,739
Another possibility - Happened to me in a boat once: There was a small piece of something floating in the gas tank, it would get sucked down and block the pick-up tube until the engine died, then it would float back up again. was really random.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
Mine did that a few times. But I had a wierd problem. Someone patched the gas tank with clear silicone. Every once in a while it would shift and plug the fuel filter. I found it by accident once. I pluuled the fuel line off the fileter and this booger thing was hanging out the end of the filter. Pulled the partially disolved silicone out (about 4" of it). It was a clear filter and you could not see the silicone when the filter had gas in it. Did that a couple more times then replaced the fuel tank and lines up to the filter. Been good since.

But I think it is a fuel delivery problem. If you can put a fuel pressure gauge semi-permenatly right by the inlet to the carb. note if you loose fuel pressure when it acts up. I bet it does. What could it be? bad valves in the pump, vapor lock, pinhole in the suction line, bad filter, the list goes on.
 
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