Help! Strange xr400 problem in Chile...

[glasswave]

I am touring on a Brazilan made Honda nx400 Falcon that is based on an xr400 motor. Today, directly after filling with gas (93 octano), it made a ppwwwfffffttt sound and died. I shrugged it off and went for a ride up the coast with a friend. I added 5 liters to a nearly full tank.

Soon, it happened again. At this point, I also noticed that when I pulled the choke out, it would act like a throttle and rev the bike up to 4000 rpm. This seems super strange. As we continued to ride, perhaps about 40 to 50 km in all, the problem seemed to worsen. Choking the bike would get it up 6000 rpm, and the pwwwffffttts became more frequent. The idle revs fell from 1500 to 1000 and I started having to keep it reved to keep from stalling. At speed the bike feels fine and seemed to be running normal. By the time we arrived back at the hostal, I noticed my bike was flaming hot!!! eeek!!

Any ideas on what in the world could cause these symptoms? I´m totally baffled, but obiviously can´t set out to Iquique until I get this sorted out.

Advice please.

thx