Heay load problem
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Heay load problem
My 1971 F-250 4x4 runs great until I pull my 22 ft travel trailer under load, up grades only. I think it is a ignition problem, like timing. New Holly 4 bbl carb on it, also new plugs, dist cap, rotor, points, condenser. Can anyone help me out with this issue? Thanks.... fish...
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From: O-O-O-Oreilly's
You're most welcome!
If its the vac advance, I am assuming it is a little down on power? It might be a good idea to check the timing again. Any issues with pinging? It is a new carb, is it adjusted and tuned properly? Is your fuel economy within a reasonable range? How does it drive unloaded?
If its the vac advance, I am assuming it is a little down on power? It might be a good idea to check the timing again. Any issues with pinging? It is a new carb, is it adjusted and tuned properly? Is your fuel economy within a reasonable range? How does it drive unloaded?
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It is not stalling, I replaced coil also, maybe jetting prob, I do not think so , but maybe, Fuel mileage is , will we all know 8-10, up hill , down , backward or sideways. 6-7 with my trailer under load is only when I have this prob. Carb new 1 yr ago. Maybe vacuum advance is not holding under long heavy load. I am not going to give up , it is prob something stupid.. I hope to find it soon
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From: O-O-O-Oreilly's
The gas mileage seems to be normal. Check to see that the vac advance is not leaking. Is it a recent problem?
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It is not firing right or something, not backfiring, not pinging, just seems to be cutting out under heavy load, I have never seen an issue like this, I don't believe it is fuel shortage because it does not do it when I am pulling hard on it while not towing. I am still going to try to figure it out some way. Thank you 351 Cleveland. I still think it is electrical, timing, advance, just don't know. ( It is since I put the new carb on it though.) Thank you both for your time and response
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Observe timing marks for smooth advance and back through RPM ranges with vacuum advance both connected and disconnected, note total mechanical "all in" timing and check vacuum diaphragm. Distributors wear out and get sloppy. They don't cost much more than a tank or two of fuel.
Newly manufactured points, and condensers, are mostly overseas crap. Only good NOS from 50s-70s or Motorcraft should be used.
Newly manufactured points, and condensers, are mostly overseas crap. Only good NOS from 50s-70s or Motorcraft should be used.
Lead Driver
Joined: Aug 2003
Posts: 7,592
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From: **** hole San Jose ca.
With all the info you gave us, it sound like your just under powered. No stalling , No backfiring of any kind, You don't say what it is really doing other then the truck won't pull your "Heavy Loaded trailer"
You may be expecting a 390 to pull any heavy load. You've run out of the power band by over loading the truck. Those f250 4wd weigh in at 5,300 to 5,500 empty.
Then add a heavy loaded trailer with a 390 eng. with xxx power has then craped out.
I think you just over loading your 390 may be go with a 460 with more TQ to do your heavy towing.
Orich
You may be expecting a 390 to pull any heavy load. You've run out of the power band by over loading the truck. Those f250 4wd weigh in at 5,300 to 5,500 empty.
Then add a heavy loaded trailer with a 390 eng. with xxx power has then craped out.
I think you just over loading your 390 may be go with a 460 with more TQ to do your heavy towing.
Orich
Fleet Mechanic
Joined: Oct 2005
Posts: 1,369
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From: Gainesville, GA
There is no vacuum advance under heavy load, only cruising with a light throttle. Now a vacuum leak is another thing. You eliminate a few things if you install a Pertronix ignition module.