wierd POPing sound on downshift - only one time

[3imo]

I was riding today. downshifted and heard a loud POP.

It wasn't a backfire. I am very sure of that.

The sound came from the carbs.   

what ya think?

[MarkusN]

Upstream "Backfires" do happen. It's normally a sign that you are short of fuel.

Also a possibility: floating valves due to high RPM during downshifting -> backstream igniting in the carbs.

[3imo]

ha!!.    On the same ride I was on my way home. the bike popped about 3 minutes into the trip.
10-15 minutes later I was on the side of the road begging a guy for gas.

I let my buddy take her out this weekend and he left the petcock on reserve for some reason.

good call.  I didn't know that. do you know why it actually happens?

[MarkusN]

Not really. I was just taugth an obviously old German adage "Wenn's im Vergaser patscht und knallt ist der Sprit zu Ende bald" (When there's popping and banging in your carbutettor your fuel is running low.)

I assume that the sinking fuel level in the bowls changes carburetion to a point where you get ignition as soon as the mixture enters the hot cylinder.

[3imo]

I spent 8yrs (total) in germany and don't know a lick of the language.

your in Switzerland?  cool.   I went snowboarding there in 03'   beautiful country.  especially from the slopes.
and the ladies....mmm....mmm...mmm

[LimaXray]

The same thing will happen on a efi engine with lean acceleration enrichments, you get backfires in the intake... probably the same idea... don't remember why it does it tho