Mark Maras

Measure the diameter and spline width. Google "9 splined shaft couplers". It also looks like Mcmaster Carr has a good selction.You may get lucky.

I wouldn't worry too much about the rise in heat after that much idling. The carbs don't need to be connected to the cooling system. The early four screw carbs had no cooling connection. I'd determine if the dampener has slipped first before buying one. You'll need to determine the exact position of TDC on #1 cyl. There are a number of ways of doing this. A M14-1.25 bolt screwed into the #1 spark plug hole (when the piston is down) will act as a piston stop. SLOWLY bring the piston up until it bumps the bolt. Mark the dampener at the timing tab TDC mark. Turn the engine the opposite direction (piston will go down and come back up) until the piston LIGHTLY bumps the bolt again. Mark the dampener at the TDC timing tab again. Actual TDC is halfway between your two marks which should be the same as the factory TDC mark on the dampener. That's a brief explanation. I'm sure there are plenty of videos on Youtube that explain it much better. I don't see how the #4 fouled plug can be balance tube related or carb related. That's why I'd do yet another dry, wet compression test. Don't ask why, it's an ugly subject and I sooo want to be wrong.

I'd weld a nut on it.

A couple of questions? Did you use a straw over the valve stems to prevent damaging the new seals? Are those plugs a new set? Don't pull the head yet. You need a good reason to do that. If you're absolutely positive you didn't damage the new seals, I'd do another compression test, dry and wet.

After a few tries at adjusting choke cables and not being satisfied, I settled on what I think is the opposite of @Captain Obvious's method. I would pull the choke knob about a 1/4" to the on position, then connect the choke cables. My logic was the choke cables having a bit extra slack would ensure the nozzles were being pushed all the way to the top by the choke cables. I lost a bit of choke because the cables wouldn't pull the nozzles all the way down but I never had starting problems in cold weather.

The flat bar (ish) choke linkage that attaches to the nozzle can cause the nozzle to bind and not return to the top. The ends of the linkage must be parallel to their mating surfaces. A slight twist to the linkage piece, with pliers, is usually all that's required to align it. Unfortunately, the carbs have to come off to check the alignment accurately.

I don't know if it's recommended but many years ago a friend and I matched piston weights by add TIG weld to the inside of some of the pistons. It was a weird project. 510 pistons in a 128 FIAT engine to bring it up to 1300 CCs. (The wrist pins were the same size) It worked for us.

I use zinc rich primer for steel. Great protection and you can weld without removing it.

Another question. Does the clunk volume increase during hard acceleration or deceleration?

Is the clunk there during acceleration and deceleration and is it louder under either condition?

You can try filling the holes with weld but you'll have to clean the rust from around them first. After removing the rust, you'll probably find you've enlarged the hole out to solid steel and have a dime or quarter size hole to patch. I can assure you that inserting a piece of sheet metal into a clean hole is much easier and satisfying than chasing a hole in rusty sheet metal with a Mig.

We may have been pioneers but we were crazy to do that. Steel wheels on asphalt and concrete had little to no cornering capability or control. We thought ourselves to be bulletproof back then but we were little more than passengers on a gravity express. No slalom course, just a schuss to see if we could stay on till the bottom of the hill. Frequently, we didn't. The adrenaline addiction stayed with me for years

Plywood and steel wheels purloined from street skates in the early sixties. Sixty years later a few of the old memories (scars) remain and remind me of the good old days of adrenaline fueled afternoons and the painful recoveries.

@PatconThat resembles the 4 barrel Carter carb we recently removed from a friend's 55 Packard Patrician. It sat under a shelter for ten years, air filter off, and the carb was filled with nut shells and squirrel pee. We got the primary throttle shaft unstuck but no luck on the secondary shaft. A replacement carb was unobtainium. He sent it to a carb. rebuild shop in Cal and got it back in about 5 weeks, cost was less than $400.00, and the carb looks and runs like new. I don't remember the shop name but if this sounds like an option I can get it for you. They were very informative over the phone.

Just my opinion, which is worth exactly as much as anyone else's opinion, but I failed to see the humor in it. From one sides perspective, this is the actual reality that they fear is on the horizon. It feeds fear, distrust, and delusion. ----- Self induced reality check. I stepped back for a moment and realized that I failed to take this from a satirical view point at first. I do hope it was intended that way. I've seen too many people who come very close to these people. I discovered I'm a bit hyper-sensitive on the subject. I love satire. My only fear is that we're seeing "Natural Selection" shift into "Impulse Power". I don't want the planet to experience "Warp Drive". I've learned to ALWAYS QUESTION AUTHORITY. I've found the Authorities on the side of vaccines to be much more credible than the Authorities on the no-vax side. Are there other options among the existing drugs? Yes. At a cheaper price? It's your tax dollar) Yes. BUT to vaccinate with new vaccines or refuse to be vaccinated are the only two choices most of us are given. Please get vaccinated.

According to your diagram, the middle wire is solid green.

Yes it does. Not enough coffee to fully engage my memory that early.

There's one more big plus using the bread method. No grease to clean out of the center of the flywheel.

I mentioned this a few weeks ago. I don't keep the components in my toolbox. To remove a pilot bushing, a slice of bread and a bolt slightly smaller than the inside diameter of the pilot bushing in the flywheel. A hammer and the bolt take the place of a grease gun and the bread acts like grease without the squeeze out.

I'd reconnect the return line. I'm surprised the engine starts to miss at 3.5 once in a while. Have you tested the pump for volume? A restriction in the supply line can up the pressure and lower the volume.

@Captain ObviousPlease define "cracking pressure when the valve is closed". I'm not familiar with the term. My point about the carbs not needing pressure is they can operate with a gravity fuel feed to the float bowls. If the float bowls will fill to the proper height at full throttle using 3.5 psi why up the pressure to 4.5? In the late 60s we ran a small dragster with a carbureted 327 c.i. Chevy. No fuel pump. Just a one gallon, non vented, fuel tank with a pressure gauge and a small bicycle air pump. We'd pump 3.5 psi into the tank, warm it up, do a burnout and just before staging the car we'd give a couple of more strokes on the pump to bring the tank pressure back up to 3.5 psi. We never experienced a fuel starvation problem.

A 1/2" x 3' length of garden hose that I use as my go-to stethoscope.

I'd love to see the specs for that "containment vessel" on wheels.

Keep in mind that carbs don't rely on fuel pressure at all. Volume is all they need and enough pressure to push or pull the fuel from the tank to the bowls. Extra pressure will try to only defeat the purpose of the needle and seat valve.

If I remember correctly, there's a reducer (restricto) in the return line. Nothing there to go bad but it could become plugged or corroded. I believe C.O. is the one who looked into this previously.