Mechanics

MISSING AND LOW VACUUM

1978 Ford F-250 • 170,000 miles

My F250 started having problems when I put gas in the aux. Tank and I shouldn't have. It started stumbling and sputtering after about 20 miles. I limped on home going 20 mph and knew it was the bad gas in the tank. I cleaned the system up and changed the fuel filter, ran all the bad gas out of the lines, pulled the carb off and cleaned it out inside and out. Still ran like crud. This time I checked the plugs-ended up changing them out with new cap, rotor and coil pickup. Pulled carb off a second time and cleaned again with carb cleaner, inside. (Even pulled jets out and blew all orifices out) Bottom line- still has low vacuum (10-13 in.) And lacks any power. Still acts like its missing for some reason. Tried to narrow down the vacuum leak by spraying carb cleaner around the carb and vacuum lines. Anything I may have missed? Oh, I also put my timing light on it and had 8-10 deg. BTDC timing. Even checked the distributor vacuum advance, it has a slow bleed off; not real bad.
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Tygnren
April 24, 2013.



If the vacuum is low like 15" or lower suspect a plugged exaust or converter. -Also these beasts as I imagine it's a 360 would wear the vacuum advance arm and or pin on the dist plate so wouldn't work very well. Also look for the pivot inside the dist being worn out. The plate won't advance right and drives like crap. I really don't think that gas is your problem. Try disconnecting exaust first and see if vacuum comes up. Try at engine first

Hmac300
Apr 24, 2013.
The truck is a 78 with a 400. I may try that. I have dual exhaust that funnels into a single muffler with a 2-3/4" -3" outlet. Seemed like it was breathing ok. No cat converter. I have plans to check compression also. Regarding the dist. Plate: I pulled the dist apart as it was in the engine to replace the coil pickup. I reassembled and put my vacuum tester on it and it worked like it should. It pivoted just fine. The old one was so rusted on there. No way the advance would work. Thanks for the suggestion.
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Tiny
Tygnren
Apr 25, 2013.

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