22-36 missing on number 4

I’m early in the process of restoring a 1929 22-36. I’ve had the head done. The bottom of the engine is good. I cleaned and put the carburetor back together. It’s the side draft brass version. I’ve put it back together and got it running. It runs on three cylinders except for engine acceleration, that is, from a slow idle to a fast idle. During the acceleration, it hits on four, then back to three. The plugs in cylinders 1, 2, and 3 are dry and clean after running. Number 4 is not as clean and slightly wet. I’ve changed plugs (using both 3076’s and 3077’s). Plug wires are new. I’ve changed magnetos. The current magneto throws a good ¼ inch blue spark and starts and runs an F-20 fine. Compression on all cylinders is about 75 lbs., and can be verified by a hard pull on the crank through all four cylinders. I’ve squirted oil around the rear intake manifold gasket while it is running to check for vacuum leak with no change.
I feel like it must be a vacuum leak, but can’t figure out where it could be considering the construction of the head (primers are gone with brass plugs in their place). All the valves operate smoothly and all have more than sufficient lifter to valve gap.
I have three running F-20’s (one overhaul and lots of tweeking on them), so I’m familiar with the engine type. I’ve about run out of ideas and any help would be appreciated. If you think conversation is in order, send me an email and I’ll call you on my dime.
Thanks, Roland

take the mag cap off & check the carbon brush contact & spring on number four, bet it's either broken or not making contact through the cap, except maybe except at full advance.

Youve changed mags and its still doing it,put another # 4 wire on it.Obstruction in the manifold?Remove the valve cover and watch the valves as the motor is running,with # 4 plug being wet its got to be lack of spark.Was your head checked for cracks,Im just rambling

jimmy

Well, if you have changed mags and plugs, I'd try changing that one wire even if it is new. I suppose it could be an internal leak. Are your primer cups closed?

Pardon my ignorance about this engine.
In combined intake/exhaust manifolds there may be an unintended leak (break through) between exhaust and intake "channels", causing it ot run lean.
My 2c, Hendrik

Thanks for the suggestions. I'm going to stay with it until it's running correctly.
Roland