1977 Ford F-100 - Suddenly running like crap


Old 05-09-05, 07:09 AM
kc robertson
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1977 Ford F-100 - Suddenly running like crap

Please Help!!!

I have a '77 Ford F-100 (6cyl - 300) that - all of a sudden - is running like crap. I don't know if I ran some bad gas through it or what...
About a week ago this started...

When I start it in the morining, it runs well. When I get out on the highway, it runs well. Once it's warm, and at an idle, it sputters and coughs and emits horrible fumes. I don't know if it's me, but it seems to be using more gas, too.

I changed wires and checked plugs, but I think it must be carb related.

There is also a hissing noise that wasn't there before - it's very noticable after I turn it off.

Any suggestions would be greatly appreciated.... I'd love to keep this thing running.

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Old 05-09-05, 08:31 AM
the_tow_guy's Avatar
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Join Date: Feb 2001
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I would be thinking either the choke is sticking and not fully "unloading" or you have a problem with the float in the carburetor - either the float needle is not fully shutting off the flow or possibly the float has become waterlogged, not an uncommon on the old carbureted stuff. To check the choke, just get it warmed up and remove the air cleaner lid; the choke plate should be fully opened, If not, check for linkage hang-up. If the choke is not fully unloading and you can't get it to work properly, one cure is to replace the "automatic" choke mechanism with a manual, cable-operated one like in the good old days. You'll have to listen closely to the hissing noise and try to pinpoint the location.
Old 05-09-05, 08:33 AM
Join Date: May 2004
Posts: 341
There are lots of things that could cause that, so looking over the engine for cracked or disconnected vacuum lines would be first. I spray wd40 around areas I suspect, if the speed climbs there is a leak there. A coil can start acting bad after heating up which would cause missfiring and condensor (near points in dist.cap) could be bad (more likely wouldn't work all the time). The slow speed circuit in the carb could have probs like the air screw could have fallen out(highly unlikely) ,etc., cracked spark plugs, rotor, cap (all tune-up stuff should be changed as it is cheap and needs to be done sooner or later. Definately change plugs. Could be fouling at idle. Hissing noise indicates vacuum leak (vacuum assisted brakes?). good luck
Old 05-09-05, 10:14 AM
kc robertson
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?!?...I did just change my brake pads....?!?

Thanks for the response...

I just changed pads on the front of my truck the day before this happened....

I didn't remove the calliper... I just pushed it back with a C-Clamp.

could it have caused/ be related to a vaccum leak?
Old 05-09-05, 06:39 PM
Join Date: Dec 2002
Location: Pittsburgh, PA
Posts: 553
I read your description, the hissing after it is shut off caught my attention. Do you by chance hear hissing near the brake pedal inside of the truck? Does the hissing change when you push on the brake? I blew a diaphram in a brake booster once and it did what I described. Remember, you have a huge vacuum line running from the manifold to the booster. You could disconnect and plug the booster and see if the idle changes of if the hissing stops. Don't drive it if you disconnect the booster.

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