Rough at low rpms
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Rough at low rpms
So I just bought a 1986 ford f250 460 4x4 and it's running really rough at lower rpms and almost sounds like it's miss firing. I don't know a whole lot about the truck or that motor can anyone help me trouble shoot this?
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It has a Edelbrock carb on it that's really all I know so far.. I'm 18 and just getting into the truck world and am basically a noob but I want to make this truck run well and last a long time as it is a daily driver as well as offroader
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Joined: Jan 2001
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From: Virginia
Take the aircleaner off. Then get it to idle by itself as well as you can. Does the exhaust smell rich? If so, while it's idling get a flashlight and carefully crawl up there without the fan chewing you up, and look down inside the carb as it's running. Do you see liquid fuel going into the engine? If you do, the float level inside the carb is too high. Probably there is a piece of dirt under the carb needle. Or this truck has sat for a few months and the fuel has gone stale, gumming up the needle.
If you see liquid fuel going down the throat of the carb, I would rebuild the carb first.
If you see liquid fuel going down the throat of the carb, I would rebuild the carb first.
Laughing Gas
Joined: Apr 2013
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Over the years most of my 460 low speed rough running problems have been bad wires and vacuum leaks.
Check and make sure all the plug wires are firmly seated on the spark plugs and distributor cap and see if that helps.
If the wires, spark plugs, distributor cap, and rotor are old and funky then it's time for a tune up and replacing them all could likely solve your problem.
Too check for vacuum leaks remove the air cleaner, start it up, and spray a little carb cleaner or starting fluid around the base of the carb and vacuum lines and ports around the intake. If it suddenly smooths out for a moment then you may have found a vacuum leak that need fixing.
Check and make sure all the plug wires are firmly seated on the spark plugs and distributor cap and see if that helps.
If the wires, spark plugs, distributor cap, and rotor are old and funky then it's time for a tune up and replacing them all could likely solve your problem.
Too check for vacuum leaks remove the air cleaner, start it up, and spray a little carb cleaner or starting fluid around the base of the carb and vacuum lines and ports around the intake. If it suddenly smooths out for a moment then you may have found a vacuum leak that need fixing.
Cargo Master
Joined: Oct 2005
Posts: 2,298
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From: NJ
Spray out the air bleed with carb cleaner. Hold the can of carb cleaner with hose on the nozzle right to the air bleed and a quick full blast in each, safety squints engaged.
Check where the idle air mixture screws are, they are probably around 1.5 turn out each. Lightly seat them and turn 2 turns out for each. One at a time turning in until idle drops, then back out 1/8 to 1/4 turn. Repeat this again. They should be about the same turns out for each side.
Check initial timing and that it advances properly. Initial timing spec is probably fairly retarded for emissions reasons, but 10* initial is a safe number for better performance. Repeat idle mixture adjustment after setting initial timing.
Of course check cap, rotor, and spark plug condition. Clean or replace as needed. Check condition of wires, too much resistance can cause a misfire particularly if other components are in poor condition.
Check where the idle air mixture screws are, they are probably around 1.5 turn out each. Lightly seat them and turn 2 turns out for each. One at a time turning in until idle drops, then back out 1/8 to 1/4 turn. Repeat this again. They should be about the same turns out for each side.
Check initial timing and that it advances properly. Initial timing spec is probably fairly retarded for emissions reasons, but 10* initial is a safe number for better performance. Repeat idle mixture adjustment after setting initial timing.
Of course check cap, rotor, and spark plug condition. Clean or replace as needed. Check condition of wires, too much resistance can cause a misfire particularly if other components are in poor condition.
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