Help! My 72 f250 (360) starts and runs well but backfires thru the carb and loses power on upgrades at 60mph or more. Plug wires are new. Please help, no F250 should be creeping along on the shoulder as chevies whiz by! I'm spending a fortune replacing burned air filters, too.

 

Have you by any chance checked your timing? Then again it could be something else. Fords are finicky after all. But then aren't we all?


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Joe, I think just maybe you posted your answer with the new wires. Sounds a little likely to me that you have a couple of wires crossed.


John
jowilker

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

I had the same problem this summer, I chased it through the carb and timing before settling on another set of new wires. After pulling the wires off, I checked the resistance through each one. One of them was bad, after closer inspection, the end that goes into the distributor was charred and not making good contact. Even though my wires were only 4 months old, something burned the conductor off the end. Be sure to check all your wires and nothing is cross-firing.


Dave,
79 F-150 4X4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished

 

HI! you failed to say if your truck has point ignition. the year of the truck says it has.i would be in stalling a new set plus a new condenser/ if the points are set with too wide a gap, it will cause backfiring through the carb. hope this helps. good luck.

 

thank you all for the tips. Despite the many suggestions, my mighty F250 continues to backfire through the carb if I try to maintain 60mph up hills for more than a few minutes. I can keep up with traffic on grades for a thrilling few minutes, though. I've checked the timing and made sure all plug wires are going to the proper plugs. Some wires cross to achieve correct routing. I routed #7 and #8 wires as far apart as practical. Wires are only 1 week and one test drive old and look OK on an ohm meter. Previous owner replaced points with white "igniter" pickup. This unit has no visible air gap between itself and green tape-like material on the distributor shaft, but shows no sign of rubbing. Is it properly installed? Could my truck be rejecting this non-Ford gizmo? A friend suggested I look at the carb's power-jet diaphragm. I did. It's fine. I have heard that the resistor wire from the ignition switch can break down and cause backfiring through carb. Does the '72 Camper Special XLT with automatic have the resistor wire?

 

Joe your timing chain could be slipped or streatched. I have thought it was in the timing somehow. It is hard to deceifer from behind a computer screen. :-)


John
jowilker

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

 

you may need to check for a burned valve, that is the problem with my 390

 

Have you done a vacuum test, or put a vacuum gauge on the old girl? I'm wondering if your advance is working right, might be something to check, pretty easy to pull the line and plug it off to test. Especially if it was one of those dual diaphragm gizmos that advanced on decel too (if OEM), might not be getting the timing it wants or needs, especially under heavy load.

 

try spending as little money as possible before looking at the heads. if no valves are burned, it would only cost 35 to put everything back together.

 

does it idle smooth.backfiring is caused by cracked dist,cap,crossed wires,pushrod off,head gasket blown between cylinders,out of time,bent intake valve.

 

maybe you have to richen the mainjet.

 

OK, before anyone jumps to club me just listen.. i know it may sound stupid, but check your voltage( battery/alternator).. my alternator is putting out VERY low voltage, but since im broke as crap right now i just stick it on a charger every 2-4 days. About 2 weeks ago i was trying to make it home as it was dying and for about 3-4 minutes before pulling in the driveway it was back firing like crazy. but only under hard throttle.. I doubt this is your problem, but always good to eliminate easy things first. do you still have your old wires? i would put them back on and see if the problem goes away. if so get another set of wires..

 

Hmm yup sounds like over heated exh seats causes by unleaded gas. If the head have never been converted to run the unleaded gas. Or Very common problem. The unleaded additives does help. But it will not correct a burned seat or valve. But if you using the lowest octane gas this adds to the problem.
Burning seats start out on a heavy pull like your doing up a hill or with a camper on it trying to pass another vehicle and it take a nose-dive popping back out the carb. Also could be a combo of intake gasket bad and burned valves & seats.. Do a compression test first. Then no more guessing games. ...
orich..