When it starts, does it get worse with acceleration? If, when the buck/hesitation/misfire starts, you press on the accelerator harder, does it get worse? If it's fuel supply it will generally get much worse when you accelerate.

Hmm, I hadn't thought of that, but no it doesn't.  So I'm guessing that it is an electrical issue.  Coil?  Points? Plugs?

@bowtiefan 

Hi Ken

I would check the point gap.

If the gap is too wide, reset it.

If it's where it belongs, narrow it up .002" anyway and try that.

We had a combine engine that ran at 3000 RPM that would miss at full speed but was fine below that. (you are probably running about 2750-2800 at 60 mph if you are running the stock 3.70 rear end)

We always had to run the points a few thousandths narrow, then it ran and performed just fine.

Essentially, the problem may be a slightly weak coil that just isn't getting enough saturation time at higher speeds.

Narrowing the points a little will increase the saturation time a little and may be enough to do the trick.  (remember to check the ignition timing afterwards)

Also, when all else seems fine, try changing the condenser.

Condensers can do weird things.  🙂

Thanks, I'll give those ideas a try.

Ken

Well, when I got into it, I wasn't real thrilled.  I found the contacts in the distributor cap were corroded as well as the rotor, and the coil wire into the coil as well as the coil itself were corroded.  I cleaned them as best as I could, put in a new coil just for luck and set the points, but not much changed.  So, I have a new cap, rotor, points and coil on order.  Hope this works.

Ken

@bowtiefan AS mentioned by Stovblt don't forget about the condenser. 

. 

Oops, I meant to say I put in a new condenser, not coil.  The coil is on order.  Thanks for catching that.

Ken

If you recently replaced the fuel pump, be mindful that the fuel pump has to have an ethanol resistent diaphgram.  There's a special kit available that works, but you have to rebuild it.  I went thru this issue with my 56 and 57 Chevys. Just another thought to go with the other suggestions.

After some fits and starts, waiting for parts and a rebuild of the carb, I got all the ignition parts replaced.  New cap, rotor, condenser, points, coil, and it still bucks at highway speeds.  But more problematic is the issue that started all this.  I had recently replaced the fuel pump, maybe a month before when on the freeway, it suddenly lost power.  It seemed to still be running, but it would not keep up.  I tried dropping the clutch that seemed to work sometimes, but it continued to slow down to nearly a stop even though I was pumping the gas pedal and then took off and continued to run normal for a few miles and then it started all over again.  I first thought it was water in the gas, but after putting 3 bottles of some stuff to eliminate water problems it continued.  I don't know if the two issues are related.  For the electrical I'm wondering about the plug wires or maybe the plugs.  At lower speeds it runs fine.  As far as the lose of power, the only thing that I can think of was the fuel pump even though it was new.  I've cleaned the fuel line from the tank to the pump by running an old speedometer cable in my electric drill and the blowing it out with my compressor, so I'm sure there is nothing in the line.  I haven't dropped the tank, but I'm saving that as a last resort.  Once when it died completely, I opened the hood and checked the glass fuel filter, I had changed the filter earlier, and it appeared full.  I'm at a lose.

Thanks for any help

Ken

@bowtiefan 

Hi Ken

Are you saying you have not changed the spark plugs?

Question... are you by any chance using a lead substitute/octane booster in your gas?

I have had 2 vehicles where I was adding a lead substitute (note: not the old lead "supplement") to the gas thinking I was doing the engine a favor.

In both cases the engines eventually started to run rough, with the problem first showing up as missing when accelerating.

Like you, I tried about everything except the plugs before figuring this out.

I thought "it can't be the plugs, I just put them in".

I even had the carburetor off the '46 twice.

Eventually I discovered that the additive was depositing something on the spark plugs that was shorting them out.

I couldn't actually see anything on the plugs, but a new set completely eliminated the problem.

When it happened again, I stopped using the additive.

Just a thought.  🙂

After I rebuilt the carb and made the correct adjustments, a couple were way off, the off idle is much better and otherwise all seems good.  I did pull one plug and it looked good, but I'm still wondering about them and the wires.  The coil wire was corroded in the coil.  I cleaned it as best I could, but I still wonder if that maybe part of the problem.  I'm considering new wires because of this.  I'm not using any octane booster, so that can't be the problem.  I'm also considering a new fuel pump as well, even though I've replaced it once already.

Ken

I had the same thing. Ran fine then not. As you're hearing from the rest of us, it really is just a puzzle to figure out. And... as much as we'd all like to suggest otherwise, it is never just one thing. It sounds like you're removing one obstacle after another and that is good. No one ever said old cars were easy to love. So here's another thing to watch for. Old fuel tanks will never be REALLY clean. Therefore they will continually be sucking up crap and feeding it toward (or into) the carbs.

On mine and now that I've hopefully pull up all the bigger stuff, I'm finally only seeing the finest particles accumulated in my filter. But those are still enough (if I don't keep a close eye) to clog the filter and therefore the line to the carbs and kill the engine. And then to throw me off a little, when it DOES get clogged enough to die on me, if I pull over and sit for just a few seconds, the crap will settle a little to the bottom, unclogging the filter a little and then it start back up and runs fine. Five miles later... rinse repeat. 

Solution: If you don't already have fuel filters, add them and monitor them often. One before the pump and one before the carbs. Get the kind that's paper and a clear outside so you can see what's going on. They're cheap and they work. The pretty glass and chrome ones with the screen inside is way to course. The inclosed metal ones work fine I'm sure until they don't. At which time you'll never know they're clogged because you can't see. 

And finally, this might not even be the problem nor the solution... but more filters can never hurt.

I pulled the tank and found a thin piece of plastic, about like saran wrap, a couple inches square.  Pretty sure that was my main issue, but I hosed out the tank and did get some small junk out.  Someone had coated the inside with some type of sealer.  I've heard that that eventually goes bad.  Anyway, I put the tank back in, changed the fuel pump and filter again and still had the same issue, but not quite as bad.  The fellow I talked to at The Filling Station suggested it might be the gas cap, so I took it off and drove into town without a problem and I was real hopeful, but on the way home it happened again.  I have given up and I have a new tank on order.  Keeping my fingers crossed!

Kind of a moot point now but when I had mine out and was attempting to clean it, I dumped in a bunch of nails and shook those around for awhile. Figured that'd break loose whatever was still hanging on and for the most part, it did. I'm in a pretty dry climate here so im going to assume it'll be ok. I painted the outside and left the inside alone. Did I mention Filter, Filter, Filter? Let us know if that fixes it.