2N still sputtering

Hi guys. I have been keeping an eye on all the recent posts on rough running issues to try and figure out my '46 2N 6V 'missing' issue. She starts reasonably well. It has started down to 15F with no engined heating.
I have good blue spark. To test i am pulling a plug gap to about 1/4" but it never really sparks to the terminal tip because it is jumping back to the threads anyway. Do i need to get a spark gap tester to make sure? I run her on 3 cylinders for a while to make sure it is consistently making. Looks good on all 4 cylinders.
I have decent fuel flow out the carb. I think i could get a pint in 2 minutes as has been mentioned in other posts. I have pulled out the carb screen and bowl screen to verify and clean. In fact, i am soaking the bowl screen to get the last bits of crud off of it and just running w/o it for a day or two to test.
I have replaced plugs, cap and rotor recently, mainly because I had them laying around. Still a sputter. Sputters/misses throughout the whole throttle range. It seems to sputter just a bit less when I have her loaded up with the finish mower or shreader on some decent flora and fauna.
I have cleaned the air intake screen and replaced the oil in the breather cup.
When she's running, I can pull the choke and she shuts down. (normal)
I do think it needs a rebuild on the engine so pressures at cylinders are probably lower than spec, but as long as she starts and I can tune the carb for low smoking I am putting this off for now.

I think i have two more things to check: 1. remove the screen (if there is one) inside the fuel tank checking for blockage and 2. check for manifold leaks. Besides doing these things, what other things can you think of?
When checking for manifold leaks, is using the ether spray around the manifold seams still the best way, or are there other ways to check for this?

Other carb issues possible?

Thanks for your help.

Did you do a compression test?

sputter / miss when running?

do a wet / dry compression check.

have you pulled the valve covers and checked for a sticky valve?.. might have one marginal one.

condenser ???

"To test i am pulling a plug gap to about 1/4" but it never really sparks to the terminal tip because it is jumping back to the threads anyway."

This caught my eye, are you grounding the plug to the head? or holding it away 1/4"?

just grounding to the head. Just letting it lay up on the head.

I have an extra one of those i could try.

Yes. I am afraid to check compression. I do forsee low comp on at least one of these cylinders. If my plugs are coming out dry though can I rule this not being my stuttering problem for now? I know my 437s are burning some oil, I'm trying to push off the ineviditable (sp) or do I just live with the stutter for now if that is the case.

Why think you have good fuel flow out the drain plug? Measure it! If you have good flow, a pint in 2 to 3 minutes, then the stand pipe in the tank is not plugged.

But that said, if the flow was blocked it would not run at all for very long.
You might fire it up in the dark and see if any of the plug wires are shorting out. if you have the wire tube, it might be hard to tell tho.
assume you have adjusted the carb at full throttle. some say two turn out and leave it along, I don't agree with that, each carb and engine are different and the carb needs to be adjusted for the engine it is running on.
I agree with the valve problem idea. Compression check will help with that idea.
Good Luck

Or to say it another way, i am a chicken in holding the wire and plug while it is running. I guess i could find something insulated to hold it away from the head that far.

2ruNgineer,Do you have a plug or two that is fouling out,if so get some non foulers.
Non Foulers