I've had two occurrences so far. When bike sits for a week and I go to start it it starts rough and I need to play with throttle to keep it running. Takes several minutes 3-4-5 and it clears out. Yesterday same thing but it started to back fire. This went on and off for 3-4-5 minutes then cleared up. I'm in Florida now (Tampa area) and there has been a lot of moisture in the air and its rained a few nights ago. (I don't have a garage so its parked outside.) I put a large piece of plastic sheet over the gas tank covering the air filter and then a full motorcycle cover while its layed up. It has a Mikuni HSR42 carb, K&N air filter and the OEM air filter box/ chrome round covering the air filter. I think there was a 1/4 tank of gas and I went and recharged the tank after it settled down. The backfiring is similar to running with only 1 coil wire attached....I checked this and there both snug. The air filter was cleaned and sprayed per K&N about 2 months ago. Coil & plugs have about +/-10K miles. 70K miles on bike and when running its runs and pulls normal/strong with no hiccuping on acceleration on gear changes or at highway speeds. TIA for any input.

 

Sort of sounds like your enricher is not enriching.

 

Or a vacuum leak when the engine is cold, intake manifold seals, voes switch, does you bike have a vacuum operated petcock? all things to check for proper operation and all places for a vacuum leak

 

and 10k miles Id throw an other set of spark plugs in her and try that first

 

- I don't think I've used it since I installed the carb but I will pull everything off around carb for a closer inspection. I have the carb manual and will poke my way thru it. thanks!
- No vac on the petcock
- Retract 10K plugs less than 5K on the current plugs.

 

So you replaced the carb? have you had a chance to jet it properly?

 

Mikuni HSR42 carb can be a bit tricky to jet and tune

 

Jets same as delivered. The carb swap and set up from FI was some 3-1/2 years (10K miles) ago.

All good suggestions and will run all to ground thanks!! .

 

Sounds Intake gaskets dry rotted or vacuum hose on the Voes

 

I had time over past two days to go over the bike. Nothing seems to be out of place. I lubed the throttle linkage and that's about it. It was time for a new battery after 3.5 years. On the startup last week the battery was just a breath above dead and getting the engine to crank enough to fire wasn't going well. Also pulled the primary derby cover to check fluid level, topped off, and check the bendix gear and ring gear and all looks ok. Got the new battery in and it fired right up to normal idle. No backfire or hesitation, smooth. Went out for a hours ride and all normal. I appreciate everyone's input.