backfire.. then sputtering. ?

[Toddxs650]

Hello again, after a ride for about 20 min on city streets, a small backfire then sputtering still runs but not full power "sounds like loose spark plug wire?" i checked all sparkplug wires. ign.coil sparkplugs/ gap all ok, also voltage at idle reads 14.20 then at about 2000rpm reads 14.42 volts. and befor ride 12.70volts In the past it would run like crap with low voltage, once left me stranded and did'nt even start, but fixed that problem with new battery/Brushes and rewired the bike. I only run headlight on a switch only at night/taillight, kick only.I hope it's not the carb because i don't know much about fuel/ air mixture adjustments and needle valves. i'm Running duel mikuni carbs on a bracket/linkage with a inline filter that is clean, so is the petcock. And i don't see any gas leak/ seals ok. please help, Thanks Todd

[Toddxs650]

Follow up,I checked sparkplugs again,cleaned them narrowed gap a touch. Then started and backfired once, but runs great "for now ?".Question now what's the best sparkplug /gap to run now on a 1980 xs 650. Fyi I took old plug from clutch side it was dry with a little black carbon buildup. The stator plug side was wet with oil and black carbon, that also was the side Carb the backfired. fuel /air Setting. To rich /lean? PLEASE HELP Todd

[drooling-bloodhound]

Here is a link you will find the gap settings. http://www.biker.net/650_service/650service%20main.html

Black and sooty is too rich.

Make sure your carbs are syncd then check timing as well and you should be pretty well off. I gap my bike about twice a year.
I run these plugs
NGK Iridium Spark Plug BPR-7EIX

[Toddxs650]

Hello i'll check, carbs+timing. Does look sooty on the left side.thanks again.