one cylinder not firing at low rpm

[TR5TRIDER]

Esteemed listers,

My 96 Steamer will run on all three cylinders above 3k rpm. At idle and up to about 2500 nothing from the #3 cylinder give her some stick and sail right on thru 2500/3000 rpm zone and she pulls strong after that all the way to redline. I can actually touch the #3 exhaust header w/out burning my fingers. Checked compression and have virtually the same on all 3 cylinders.  Checked for spark and have same. Changed spark plugs, coils and wires and no improvement or change. Did note the new plug installed in #3 smelled of gas and did not turn black but only ran for a short time. 
I am thinking too much fuel, have just pulled carbs and see that the floats are set at 12.5 mm rather than 14.5 mm that Haynes recommends. Have pulled float assembly from #3 carb and see that orings are past their sell by date ( cracks and loose fit around float assembly). The needle valve looks OK with only some polishing where the rubber tip seats on the plastic float assembly. How critical is float level? I am thinking that I am seeing an additional 2 mm of gas level in carbs, and that is all 3 of them but only the #3 cylinder is misfiring.  I know that the float assembly orings need to be replaced. I am thinking that the low  speed dropping out of the #3 cylinder is caused by too much gas and that as the engine speed increases to 3k zone the air to gas ratio changes to bring in more air to the volume of gas and this allows combustion to begin.  Am I on the right trail? All advise and recommendations are encouraged.

TR5TRider

[Mustang]

Replacing the o rings will cure it .
Fix those pronto.

[TR5TRIDER]

Thanks Mustang, will do.  Have a bagful of the little buggers that I ordered from McMaster Carr.  Will head out to the barn after supper with a beer and some orings.

[TR5TRIDER]

I started on the carbs last night and finished with them (new float assembly orings, cleaned pilot & main jets and all passages) this morning. I then mounted carbs on bike w/out air box to check for leaks and to run engine and synch the carbs. Now synched and sounding much better as they were way out of synch. this afternoon removed carbs and put air box in frame then set carbs in place  and it is now early evening and cannot get air box boots to slip onto carbs. Not my first rodeo Joe, as I have a Sprint also and have had the carbs in and out several times. I am done! Tomorrow is another day. All forking day and haven't got her back together.This is definitely a love/hate relationship. Anyone have success with binning that brokedik air box??? If so I want to know about it.

[Mustang]

Leave the boot clamps loose on engine side of carbs and lift the rear of carbs .
Voila air box slips right on .
Get the #1 air box boot on first and tighten down clamp
Don't worry about if the other two come out
Now get #3 on and tighten boot clamp
At this point #2 should have slid on by itself. Tighten the clamp.
Don't forget to tighten the engine side boots now.

EASY. RIGHT?

[TR5TRIDER]

Must go see eye Doc. this A.M. will try as you say.maybe this evening. The engine boots when sighted from side view appear not to be symmetrical (clamp grooves are not parallel) what should the orientation of these boots be? I placed them with the greater space between clamps at the top.

TR5Trider

[Mustang]

You have them right

[Sin_Tiger]

A hairdryer helps if it's not warm, which is most of the time here 

[TR5TRIDER]

Went to the barn after dark in the cool evening air (77F.) and in a short time had air box boots in place and secured also remembered to tighten clamps at engine side, did not resort to hair dryer. Thank you all. Now for final check on synchronization then a test ride.

[qbto]

My moneys on you have a duff coil !

[TR5TRIDER]

Back at home base after several weeks with grandchildren on Gulf coast and West Texas. Put the plastic back on bike and did some hwy. miles..... how sweet she runs now. I am in love again, what a great bike. Thanks to all for the helpful advise. Now for some work on me Sprint, if I can stay off of the Sprint.