I have a 1970 F-350 with a 390 in it and I am having a hell of a time finding the problem to my truck. I just can't get it started anymore. It has been starting on and off. when it doesn't start, it sounds like the battery is dragging sometimes it will catch and start up but it's to the point now that it won't start at all. First I replaced the distributor, coil, wires and plugs. started right up and purred after dialing in timing. Then same problem, sometimes sounding like battery draw. I have since replaced, all battery cables, alternator, voltage regulator, starter solenoid, rebuilt the carburetor, I pulled the starter and ran juice through it and it worked fine..... WTF can be causing this thing not to start. at my witts end..................................

 

It could be a weak starter. Yes I read what you said about pulling it and running juice through it. Also could be a weak battery if you haven't replaced it. Did you time it with a timing light, vacuum line unplugged if it has one?

 

ya, brand new battery this morning. and it turns over fine for a while, then back to acting like battery is real weak. batteries should not go weak this quickly.

 

TRUE. Are you sure the new battery was fully charged? They should be and usually are. Maybe the battery was sitting on the shelf a long time. Does the battery have a build or ship date on it?

 

Once started and running, the voltage at the battery should be 14.2 to 14.8. If it's less the alternator isn't putting out right or it could be in the voltage regulator. My 74 F100 has a separate regulator next tp the radiator, I assume yers is the same. If you have the correct output and voltage at the battery, you may be having issues with the voltage being pulled back into the alternator via a bad regulator with the key in the off position, assuming a stock system. If it has an alternator with the regulator inside, the final diode may be bad and allowing voltage to seep back into the ground via alternator. This is easy to check. Take the large wire off of the alternator with the battery hooked up like normal. If you see any small amount of arching, you're losing voltage back to ground. Another area to check out and this is real easy, make and connect another ground strap from the engine to the frame of the truck. Sometimes this helps a lot with the older trucks as the old one gets corroded over time. Without the proper ground, nothing works right.

 

well now it's trying to start turning over. had a big poof now I have smoke coming out of the breather.... think the engine might be blown...... and thats why it wont run....

 

Labnerd, this issue has been happening both before and after replacing both the alternator and the voltage regulator, which are separate items.....

 

If you have a manual transmission you might try giving it a pull start. If you try doing a pull start don't forget to turn the ignition switch on. If you have an automatic transmission that idea is out.

 

Pull all the spark plugs and do a compression test - if it will turn over fast enough.

 

Smoke from the breather doesn't mean it's blown. More than likely since it didn't start, gas accumulated inside the engine and it fired off in the crankcase causing the "poof" and smoke. Sounding more like the engine has jumped time. I'd still suggest the extra ground strap. It can cause all kinds of issues. If you have a timing light, I'd take a look to make sure it's in time. If it's in time, that is, the timing marks line up as the dizzy fires, it can still have a cam that's out of time. That engine has points and condenser. Have they been changed out? Gap on the points should be 0.017 and if you have a dwell meter, that's 26-30 degrees. Bad points can cause the issues you have.

How many miles on the engine? Has the timing chain ever been replaced? Has the truck ever backfired while it was running? Do you get any backfiring thru the carb if you hold it wide open while starting? You do know that if the carb catches fire in that fire is coming out of the carb, the easiest way to put it out is to hit the starter, It will suck the fire inside the intake and just burn all of the oxygen in the intake and go out. You can use a wet rag too by throwing it over the carb.....that's wet, not dripping water.

 

I was thinking that it might have jumped timing.... all new distributor, with new points, not sure how many miles on engine, says 81,000 but don't know how long speedo cable has been out. It's a big truck and probably hasn't done much time as a daily driver. Like I mentioned, it was running fine, then sputtered and died.