Usually what I've seen with running straight 12 volts to points is harder and harder starting over time, especially hot, and popping and backfiring under hard acceleration. Does your truck have metal timing gears or the cam gear of fiber? It almost sounds like a timing gear coming apart.

 

The truck did get progressively harder to start in conjunction with losing power. I picked up a new set of points, condenser, and new spark plugs. It already has new cap/rotor/wires so there will be nothing left to change once I install the new stuff. If that doesn't fix it, I'll look into the electronic trigger conversion.

 

If doing all that doesn't fix it I would do a vacuum test. If it does fix it, check the voltage to the coil. You may need a resistor block or resistor wire to get the running voltage down to 6v and the starting voltage to 12v.

 

I went out to replace the points yesterday and couldn't find them in my "unique" organization and storage system... I tested the coil and got 1.5 or 1.6 ohms so that's right on spec. The voltage at the (+) terminal was 6.1 and the (-) side read 0.2. My dwell meter is probably stored right beside the new points along with my feeler gauge set. I decided to quit being a cheapo and contacted Pertronix about getting an Ignitor trigger. They said the model 1281 fits these trucks so it's ordered and should be here in a few days. Since others may be looking for this info, here's a few pics of what I'm working with.

 

I found my new points and condenser. The dwell meter was not with them. In the interest of being scientific about figuring out what was wrong, I decided to do one thing at a time and see what happened.
1) Adjusted the points. They were WAY too tight at about .008. Adjusted to .018. Tried starting. No luck.
2) Replaced all the spark plugs. Tried starting. Fired right up, but didn't quite seem to be running as smooth as I hoped.
3) Connected the other 4 spark plug wires...
4) Plugged the vacuum advance line and checked timing with a dial-back light. It shows 10-11 degrees at 800 rpm and goes up around 15 at 1500 rpm. I reconnected the vacuum line and snapped the throttle a few times to watch for some vacuum advance. I couldn't really see much difference. Not sure if that's a realistic way to check it.

The truck purrs like it's supposed to, at least while it's not working. Since it's running nice and the Pertronix ignitor will be here Monday, I'm not going to install the new points and condenser. Anybody want them? Just pay shipping.

Now that the fires are lighting, I need to get the carburetor idle adjusted right. It seems to still be running a little lean because I have to keep the choke applied about half way for it to idle smooth. As soon as I open the choke all the way, it stumbles and dies. It has the 2v Holley 2300 carburetor with mixture screws on the back side. I started with them 1.5 turns out and went all the way to about 3 turns out before I noticed much difference. I still can't open the choke or it dies. I'm going to look for vacuum leaks next time I play with it.

 

OK. One last update for today... I looked up how to adjust the Holley idle mixture screws and found lots of videos and text that contradict what I was trying. The idle mixture screws are on the sides of the metering block, not the back of the carburetor. So, what the heck are these screws for?

 

I looked close at the sides of the metering block. I can see where adjuster screws would have been but the holes have press plugs in them, not screws. I guess those ports got rerouted to the screws shown in my previous picture so I was doing it right after all. Still chasing down why it's idling super lean and can't seem to get it rich enough with the adjuster screws. I might go back to a previous idea I had and solve a $10 problem with a $1200 solution. https://www.holley.com/products/fuel...parts/550-851K

 

Mr Pilotron. I can't believe nobody has replied to this yet so I'll give it a go. Btw, I share your "unique" storage system and I too have been known to forget to connect a spark plug or 4 when I got in a hurry.

Anyway I've had very good success setting idle mixtures with a vacuum gauge. I have one semi permanently connected to manifold vacuum on my C850.

Just run it a bit to get some heat into the combustion chambers, then slowly experiment with each screw, going back and forth until you get the most vacuum you can. I'd periodically open the choke more and more to see if you can get it to idle properly. What you want is the most vacuum at idle you can get with the choke fully open.


Having to run it with the choke on is a bit worrisome though. It might just be way out of adjustment but it could also just need a good cleaning. The rebuild kits for these aren't all that expensive. I did a similar one on my 60 f350 (with the idle screws on the sides) for around $25. I got some acetone and a shallow container to pour it in so I could soak parts.
The truck had been sitting pretty much continuously since the mid 90s. I had to use some tiny plenum brushes to get everything clean. .I think they were around $4 for the set on amazon.
At any rate it was tedious because almost every passage was full of hardened crud but it went back together and runs for cheap so I'm satisfied.


Have you gotten that Pertronix setup yet? I'd be curious to know if there is a noticeable difference in the spark with them. I'm tempted to get one and just keep a set of points (or my spare distributor) in the truck. I keep a box of odd spare parts in case something breaks because almost everything for it is a special order these days.

 

I went through the carburetor last year and again this spring. It was really clean to start with and I didn't spend a lot of time probing passages since it was so clean. It's possible that I was fooled into believing that the passages inside would be clear. I'll pull it apart again and probe all those little passages. I'll also look to see if maybe the gasket kit I got is missing a hole that would allow the idle circuit fuel to flow down to those alternate mixture screws since they don't really seem to make much difference. As a side note: I used the new environmentally friendlier NAPA carburetor solvent bucket. It seems to basically be mineral spirits. Nowhere near the "snort" that the old Berryman bucket had.

The Pertronix kit showed up, but I haven't installed it yet. I will do that after I put the carburetor back together again. I'm trying to only change one thing at a time in order to keep a scientific method of working out the problems.

 

Been reading as I too had carb running I issues with my 391 4V. (had to have the choke on to run). After multiple times of cleaning, reseting i got a used one from a friend for $100 and without rebuilding bolted on and FIXED!!

BEFORE you even consider a $1200 FI I would take a stab at a 2brl Holley I see them at swap meets NEW for $100. JUST so you can rule out carb and NOT deal with linkage drag on TPS, gobs of wire and patching in a high pressure pump.. (noisy on frames)

Fondly Mark
PS I WILL take the points and condenser send your PayPal with to
Mark Haas
5497 Highlawn Way
BRIGHTON mI 48114