Engine runs poorly.
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Engine runs poorly.
1974 F-100. Single points on a 302/3-speed auto. Gets plenty of spark. Gets plenty of fuel. Sometimes it will fire and then immediately die. Other times it will fire, rev high, and then slowly die. Others it will run great, but when you shut it off it won't even try to fire. Points and condenser are new. Vacuum advance only and it works good. Coil is good. Complete tune-up besides wires just performed. What could make her run so unpredictably? 
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Yes-she gets plenty of fuel. I actually had to turn the idle set screws up to 3 turns cause they were out only one a piece. I had thought about rebuilding the carb but when it runs it runs great so I was hoping I wouldn't have to. O-ya, great ground throughout.
Post Fiend
Joined: Feb 2004
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From: nebraska
Maybe its time to take it to a mechanic or ask somebody you know that is a mechanic. Tell them whats happening exactly how it acts that is the key. The more information the better. How many miles on this motor.
Fleet Owner
Joined: Jan 2004
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From: Brentwood,CA
it is possible you have a slipped timing chain it was commmon for plastic gear tips too be used and they broke off and will move the chain
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Postmaster
Joined: Apr 2000
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From: SD
Was it acting this way before the tune up? Did you use a dwell meter to set the points? Dwell should be 28-30, it's more accurate than feeler guage.
Marty
Marty
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It has the motorcraft 2bbl on it with the auto choke. I don't suspect the mechanical timing because when it runs it runs very well....when it runs. It's like something changes everytime I try to start it and I'm stumped. The distributors vacuum advance plate actually migrates all over the place when it is run so I shimmed the sides in 3 places with part of a marlboro hardpack. That seems to keep it pretty stable. It does not have a lot of dwell-I can see that. Come to think of it, the if you grab the rotor you can twist it a little, like about an inch one way. That is the only thing I question about the mechanical timing. Whew-almost makes me wanna buy a new car...well....how bout no.
Postmaster
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From: SD
Originally Posted by mary-kate
The distributors vacuum advance plate actually migrates all over the place when it is run so I shimmed the sides in 3 places with part of a marlboro hardpack. That seems to keep it pretty stable.
It does not have a lot of dwell-I can see that.
Come to think of it, the if you grab the rotor you can twist it a little, like about an inch one way.
It does not have a lot of dwell-I can see that.
Come to think of it, the if you grab the rotor you can twist it a little, like about an inch one way.
Do you have a dwell meter you can check the dwell with?
The rotor should move some and then snap back. If it doesn't seem to snap back to place - you may need a new distributer. They can be had at any auto parts store for about $35 plus the old one for core.
If you do decide to get a new dist, this would be a good time to upgrade to the duraspark II electronic ignition. Very good system, replaces points and cheap/easy to work on. You will need the module, wiring harness and dist. All can come from a salvage yard (but you may still want to get a new dist). I think there's a tech article about swapping this in (link at top right).
Any one of these three problems could cause the trouble you are having. Try to eliminate them.
Marty
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Joined: Dec 2000
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From: Garden City Kansas
He said the rotor will move an inch one way.. this is corect and should happen. Your distributor has mechanical advance in it and that is y it moves. Like marty said though it should snap back to the original position otherwise something is sticking inside of the dizzy. What exactly do you mean by the vacuum advance plate moves all over the place when its running? With the cap on and it running you shouldnt be able to even see that the advance is even working. if it is moving check the mounting bolts on it or see if the canister is broken somehow. if it is get it replaced first. You should get a dwell gauge to check the the points as it is more accurate but a set of feeler gauges will get you by. Any haynes/chilton manual will tell u how to go about that. Sounds like the carb is in a need of a rebuild. If it is starting and then reving higher than it should sounds like the auto choke isn't working right which is a pretty common prob with the age of these trucks. First check the advance. Next check the dwell as its the easiest then adjust the choke and make sure it is working right as it will cause you tons of problems if not right from not starting to running rich all the time to dieing, and then all the sudden running like a champ. If that doesn't work buy a tub of carb cleaner and take her apart and clean everything. Hope the advice helps
Dick
Dick
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I know the vacuum advance works cause I pulled the hose off of the carb and did the old suck it test. I know the vacuum advance plate moves cause I can center it and then run it and it will be in various places toward various sides when I take the cap off(usually toward the rear) The choke is sticky, but that is what I've been using one of my screwdrivers for. No-I dont have a dwell meter but with the shims it stays pretty centered so I set gap to .012 and I've checked all the hoses. Hmmmmm.
Elder User
Joined: Oct 2004
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From: Winnipeg, Manitoba
Since your choke is sticking, it might be time for at least a good cleaning in that department. Grab yourself a can of carb clean and once you have the engine running, spray it down the bore of the carb and all around the moving linkages as well to free them up. Should be able to eliminate the sticking choke problem that way. Dwell is more important than gap, as the distributor cam that pushes the points opened and closed does wear, as well as other parts. One thing I would check for is up and down movement on the rotor itself. You're checking for movement of the shaft it resides on. The easiest way to check this is to pull it from the engine. Since your vacuum advance tends to stick, I'd look at replacing it as well. I could be wrong here, but likely, if you were to gut the top end of the distributor, you'll also find two moving weights, with springs attached to them underneath where your points are attached. This is the mechanical advance, and if this truck has sat for a while, things could be a bit rusty, or possibly you have a broken spring as well. These springs are what will cause the rotor to spring back into a static position if you twist it one way.