I have a 1986 ford f150 with a 300 engine. Came home one day and the truck died in the driveway. After checking everything the problem was no fire to the plugs. Check coil, was ok, distributor cap OK, end up replacing the whole distributor, new cap, rotatory button, plugs, wires, they set timing, engine cranks now, but has rough idle, and skips, when engine is under load. If you get rpms up to 2700 skip goes away, it makes me think it has something to do with spark advance. I went to auto zone and bough a new distributor, but the one they bring out did not match my old distributor, it had a vacuum advance on it, my old one did not have a vacuum advance. They told me the old one I took out was for a 1991. So that’s what I put back in it. Does anyone have any ideal that the problem could be. I have been to three shops no one has fixed it yet need help from an expert!

 

I will take a picture of what mine looks like for comparison.

 

no, the old one is the right one for your engine/year. go somewhere else, the guy at autozone doesnt know what hes talking about.

you have the feedback carb which uses a computer to contol mixture and timing advance and does not use vacuum for timing advance.

 

and once you get the right distro in there use a vacuum gauge on manifold vacuum to set timing at warmed up idle (get it to 18")

 

I say more vacuum. Mine is rock solid and I have over 20"

 

18-20 is factory new and too high he can get PING, depends on the engine, gas, altitude etc

 

While I agree about ping, the engine is only got like 8:1 compression.

The timing is going to be set at like 4* IIRC and once it is set you can increase or decrease the vacuum as you see fit. But once you get a good 750 RPM idle the engine is only going to make a finite amount of vacuum for that timing setting.


The higher the vacuum number the better the engine will run to an extent.


Also check to make sure that the carb nuts haven't backed off. When I first got this truck it ran like crap. It had a lot of vacuum leaks. One of the biggest was that the carb was sucking in air at the flange. I think one nut was like 3-4 turns loose.

Another thing is the PCV grommet. They rot out and cause leaks.