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