Well, the list of burnt down Amazons DID NOT get a new name on it tonight!
I pretty much did everything all of you suggested before setting off and everything vent smoothely: I cleaned the valves, checked the floats (in case they would leak & fill up with gas), emptied the bowls, and followed my first intuition: the pump. Then I made it safely home with the lady...

OK, this doesn't mean I'm out of trouble, since I discovered with the filters off that the piston in the front carb would not come down by itself, leaving 3-4 milimeters between its bottom & the bridge. Looks like I'm in for a second carb dismanteling in 1'500 miles. Love it! This is not related to my flooding pronlem though. Well otherwise I should learn mechanics again...

BUT there is some info that might be useful to you guys. As you know if you read the prvious topic about flooding SU's, I was running a Pierburg (the latest model, the one you cannot dismantle) on my B20B, wich I thought was a reliable unit. After taking the pump out tonight, I checked it & there is something strange about it. I'l try to describe it with my "swiss English"...: when you put your finger on the intake of the pump & pump 3-4 times, you can hear a strong "suction release" noise when you take your finger off. Same applies with the output hose, except that it's a "pressure release" noise. Now what is odd with this pump is that when you close the output hose, the lever becomes loose after 3-4- times pumping. It feels as if the diaphragm was stopped in the "full spring compression" position, with "high" pressure built up between the diaphragm & your finger with no possible release in the pump body (through the valves I presume, although I'm not familar with the way a pump does stop pumping when the output is closed). When trying the same with another pump, you could still move the diaphragm with the lever when the output is blocked, which logically results in the pressure to be "lost" or released in the pump. On the new used unit I installed tonight (same Pierburg one, I like risk...), the release in the body was possible. In the discarded unit, when you block the output, pressure builds up to a certain point (I will measure the Psi ASAP) and then the diaphragm does not move until the output is released. But the "blocked pressure" is certainly high enough to push the floats down in the filled up bowl... and then comes the flood!

So I'm pretty amazed myself but at this point I'd say that YES, a mechanical pump can all of a sudden put out "high" pressure...

If this makes any sense, I hope it can help. What do you think of this little mystery?

Cheers!
Séb "beware of the Pierburgs!"