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my 1978 f150 has been given me problems for about 3 months now. it runs, but not the way it should. timings been adjusted, rebuilt carb, checked all my hoses, changed out spark plugs. its sputtering and backfiring through carb occasionally. i am going nuts trying to figure this one out. i have searched this forum and tried some new things but still not running right....HELP...any ideas would be greatly appreciated. thanks
also...i was thinking either i need a new timing chain or its my vacuum advance...but i was wandering what thje difference between a vacuum advance and a mechanical advance is...thanks for all the help.
why would someone plug the hose leading from the vacuum advance? i took them out, their were 2 of them, and it doesnt run any bettter or worse. their are about 180,000 on the engine. the guy i bought the truck off of swears up and down the odomoter has never rolled over but i dont believe him...would be hard to believe. i took the distributor aparet last night just to look everything over, i didnt notice anything oout of the ordinary. i thought about replacing the whole damn thing, what do you trhink?
put a vacuum line on the vacuum advance ad suck on it to see if the plate is actually moving inside the distributor. If not, the the diaphram has ruptured or the plate is seized.
The mechanical advance uses weights and as the rpm increases, the swing open and advance the plate in the distributor.
thats great advoce about testing the vacuum advance, thanks a lot, ill try it as soon as i can...the timing is correct, but i have no idea how to do the other test.
One way to check for slack without removing the cover is:
To get a power bar and socket for the crankshaft bolt.
Take the distributor cap off and slowly turn the engine one direction until you see the rotor start to move ,then stop > Now,turn the crankshaft the other way and measure how many degrees the socket handle goes before the rotor starts to turn.
Normal is about 10*
Get back here with the results.