1 cylinder not firing

A thumb over the plug hole is not much of a compression check. You could have a tight valve clearance that is letting lots of compression out but leaving enough to lift your thumb off. I would check valve clearances and then do a proper compression check with a gauge, throttles wide open and at least six kicks.

Did you verify flow through EVERY passage using aerosol solvent, like brake cleaner?

solvent. wire. air every passage, all clean and now cleaner.

Did you verify choke slides do what they supposed to?

yes

Next, take an extra spark plug, put the RH lead on it, lay it on the cylinder head. Start the engine (on the left cyl) rev it, watch for spark. Easy 2 minute test.

Done before I took carb apart. Good, strong spark, plus switching leads made no difference

had a similar problem ..... not firing on right cylinder.
Problem due to excessively rich mixture.

I believe richness to be the problem. I have the concentric carbs. I'm not sure what you mean by "the jet block gasket". There is the O ring at the flange, there is the big gasket at the intake mount, the float bowl gasket and the O rings on the adjustment screws. The screw O rings, the float bowl gaskets are new. the others look in good shape.

A remote possibility but a quick and easy one to check is the engine earth.

I double checked all grounds when installing turn signals- but if the carb reassembly doesn't do it, I'll re check that.

A thumb over the plug hole is not much of a compression check.

Yes and no- I'm not talking moving your finger, I'm talking about blowing it off when I'm pressing down as hard as I can to avoid such. So while thats not a true compression test, and the valves might be off, its enough of a test to see if the bike has enough compression to at least fire. Might miss, might run like crap- but it takes a VERY low compression to not fire at all- and I've owned antique bikes since they were new in the 70s, and know the feel of compression lost. But I take your point. And if the carb isn't the fix, valves will be my next step- I just hate taking things off that don't leak unless no choice. And since my thumb test told me they had to be pretty close if not spot on (all were set to .008 and .0010 less than 1000 miles ago) and valves rarely work themselves tight. and no unusual valve clatter, but it does happen , I skipped this for now.
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Torrential rains last night and for today, so doubt I'll get to it, much as I want to. I'm literally a shade tree mechanic.

trappnman said:

I double checked all grounds when installing turn signals- but if the carb reassembly doesn't do it, I'll re check that.

Click to expand...

On mine the earths checked with continuity on the meter, however internally hidden under the insulation there must have been a break leaving a few strands connected, only a new wire from head to battery worked as the current of 2 sparks would not pass without it.

kommando said:

On mine the earths checked with continuity on the meter, however internally hidden under the insulation there must have been a break leaving a few strands connected, only a new wire from head to battery worked as the current of 2 sparks would not pass without it.

Click to expand...

Are you talking the ground that mounts to the top of the heads? Its a new wire, but it might not be fully grounded. I did have to run a direct wire ground to my rear turn signals to ground them. Will keep that in mind, thanks.

The std engine ground is from somewhere at the bottom of the engine to a Z plate bolt. I ran the extra one from the headsteady bolt directly to the battery, then when it worked I ran it from the headsteady again to a red wire near the rectifier. I wanted to eliminate any possible lack of continuity due to a barrel gasket etc but instead it showed the normal earth was on its last legs.

kommando said:

The std engine ground is from somewhere at the bottom of the engine to a Z plate bolt.

Click to expand...

The standard engine ground connects to the head steady.

The red ground wire ring terminal (attached to the inside of the rear RH footrest mounting to Z-plate bolt secured by a nut) is the connection to ground (harness red) for the Zener diode.

Success.

Not really sure what the problem was, but 100% carb and 100% flooding condition.

I can think of only 2 possibilities:

1) that the needle cir-clip, somehow became caught on the spring. It puzzles me that both cylinders ran last year, and on several good mileage trips this year (albiet it seemed to miss a little, and definitely ran better at higher rpms) and wasn't into carbs since then, but.... Having the needle caught in the spring, would certainly cause a flooding condition.

2) An air passage was partially or completely blocked. This too would cause such condition.

I think one can rule out float bowl/float needle and seat since it flooded the bowl only when tickling, and there was no evidence of overflow during testing.

and choke cutouts were up.

So one of those 2...

Not 100% sure its 100% right- started it half a doz times (1st kick after the 5-6 on initial start w/o choke) and was strong on both sides- but only had time to ride it around the literal block- hopefully a long distance ride next day or two to confirm all is well. Running the NGKs now, see how I like them-and the upgrade on wires and caps should be a bonus.

Once again, thanks to all that helped- it DOES help...trap