Hi,


I don't typically work on things older than the 80's... and I am in a pickle. I have a 71 F250 that won't start. It will crank, but not start. I turn the key and there is no voltage on the coil. I know it should be 7-9+ volts? What is happing with this truck? Thanks for any help!

 

Hotwire the coil. Run a jumper straight from the battery to the positive side and see if it starts then

 

Remove the wire on the coil that goes to the distributor. Measure from it to ground (engine block) with an ohm meter. If it reads 0 or a very low number, pop the distributor cap and make sure the points are open. If they are, then you probably have a bad capacitor (silver can under cap with one wire coming out of it, also called a condenser).

 

If you have no voltage on the + side of the coil with the ignition switch on, your problem is not in the distributor. It is upstream, in the "pink wire", ignition switch or wiring to it.
As suggested above, run the hot wire and see if it fires. Then work back to and through the ignition switch to trace the problem.

 

hanks for the replies... I looked at the coil wiring and found a break in the +. I fixed that and it starts intermittently it takes a few cranks to turn it over... I have power, spark and the fuel is good. I took the liberty of adjusting the carb when it was running and it seems ok.


So I'm thinking the timing may be off a bit. It is picky on when it starts and bit rough. I really don't play with ignition systems on older naturally aspirated rigs past 1990.


And would a weak condenser cause the issue? Worth replacing it? I am researching now how to set the gap on the points at .017. As old as the points are they surely need adjustment.

 

Sounds like you're on the right track. Tune carb and ignition for highest vacuum rating.

 

Replace points and condenser with good quality parts. Ford stuff is best. Set timing to 6 degrees advance with vacuum line plugged. Rock idle mixture screws and idle speed back and forth until turning in idlers slows motor. Set speed to around 650, or wherever you are happy.
These motors are very forgiving.

 

6-8 is the spec, I like to run 12-14

 

Thanks again guys. Will report back with hopefully good news

 

One thing these old classics had for a couple yrs was a short good starting live due to fords screw up by putting in a sure to fail Ign key switch. They slowly cook the starting circuit.

The Ign switch has round copper terminals at the rear of it. Also the Ign. switch plug itself over heats too. This condition mimics a weak condenser. Where as the engine almost starts but fails when you let off the key.

The replacement ign switches to correct this problem has flat spade terminals with a matching plug.

So you may want to check out your ign. switch at the rear for any plug over hearting a small terminal will be blackish burnt.

orich

 

OK... just an update. I may have resolved it, but have just a last question.


What I have: Step Dads snow plow that he has basically used as a bulldozer for 30+ years- 1971 F250 4wd w a 390.


It wouldn't start. So I found a broken wire in the harness AT the coil It now reads 6.79 V w the key on.


It kind of started intermittently, then would die and not start again. So I adjusted the carb when I had it running, set the idle and looked under the dis. cap (yikes). Looked to be a very old set of points and prolly the original capacitor.


So I replaced the points/ capacitor, set the gap at .17 at the highest ridge on the shaft (sound right?). It started up on the 5th crank or so... then kinda stuttered out. Then I figured out the timing advance vac tube was broken also, ugh. So I set the timing to 10 deg advanced. Is that right? I read 6, but it really chugged, even with the vac advance set back up... at ten it starts on the first crank and has just a slight miss. Not sure what that's about, but I am sort of content to let it ride... Sound like I have this thing set up right? This old school tech is a pain, lol.

 

The voltage at the coil is correct, with the points closed. With points open, battery voltage.
These things do not much care what timing you put on them so the difference between 6 and 10 is not your issue.
The thing has obviously had a lot of neglect. Start looking around for vacuum leaks, replace rubber hoses to carb, rebuild carb, replace filters... There is a ton of information on what you have to do. Search or come in and ask us.

 

I second John. Sounds like you might have a vacuum leak. Spraying carb cleaner or ether around the carb base, intake ports can help find it.

 

Boy if I run 12 it doesn't like to start when it's hot. At 14 I would have to put a switch to the hot wire to get it to turn over enough to start. I am currently at 11 and seems to do fine.

OP, with all the trouble with cheap parts these days ie condenser, if you can't find quality points as suggested you could always switch to the petronix ignition. As many will attest hard to beat but not as much fun as adjusting a set of points.....

 

If you stick with the points I strongly suggest Genuine Ford (motorcraft) parts. Still available from Ford. And don't forget to put a small dap of dielectric silicone grease on the inner edge of the point's rubbing block.
points.....B8Q12171A (DP12).
condenser..C9AZ12300A (DC13A)