Stuck needle valve?

Just looking for confirmation on what I think is happening. If my 750 sits for 5 -6 days in near freezing weather. It will start, but it's only firing on 1 3 and 4. #2 exhaust stays cold. If I wait for a few minutes until the other cylinders warm up the engine, then if I tap the #2 carb a few times with a big screwdriver, I start getting some backfiring and the exhaust starts to heat up. The backfiring becomes more rapid then stops and I can tell all 4 are firing normally. I'm thinking the needle valve is sticking shut during the lay over and once I knock it loose and gas starts to fill the bowl, then the low amount of gas is causing it to run lean - hence the backfiring. Once the bowl is full and enough gas is being delivered the backfiring disappears. Does that make sense? The carbs were cleaned and checked during the summertime and it ran fine since then.
Does this scenario make sense?

thanks, Rick

 

I think that you have diagnosed your problem.

 

I concur.

 

With below freezing temps, I'm not too inclined to pull the rack and clean out any gunk that might be causing the problem. Anyone have any luck with any magic in a can type solutions? Or I suppose I can always just carry a big screwdriver in my pocket.

"Hey sailer .... You glad to see me?"

 

There's a product in the UK called STP Fuel system cleaner (for carburettor engines) I used it on my 125 when it had been sat for 3 months. It spewed out some pretty shitty smelling black smoke, but after a having difficulty starting it, once that stuff went through it started & ran fine. I put half a bottle in a full tank on that occasion then, once a month on a full tank put a cap full in keep scum from building up that way