Well guys all is fine finally.
I checked the fuel tank and the fuel system again like Jim Laguardia told me but there was nothing special in the tank. There was some dirt in it but nothing unusual and thank God no red death. Anyway now I'm sure this side of the fuel system is clean.
I rebuilt the carbs and they were not that dirty. After the rebuilding I checked the camshaft timing by making sure that the rotor was on the first cylinder when the piston was at TDC at top compression. All was fine.
Tune the carbs and the ignition at 7 degrees at 800 rpm. Both carbs are at 10 on the scale on the balancing gauge.
Now everything is back to normal, the Pinz start as good as ever and I have good power at all rpm.
One thing I did was to check if I was taking air in by the Eberspacher fuel system, remember it is a K. I never had problem with it but I haven't used it in a long time and maybe there was no fuel in that side of the fuel supply. So I start it to make sure the fuel line was fill and not leaking anywhere. The Eberspacher pump a little at the begining but after the first priming it was as usual.
I don't know for sure but the back firing in the carbs is due to low fuel supply to the cabs. Now by cleaning them I'm sure that the fuel is going to the cylinder properly. I will rebuild all the fuel system to the Eberspacher when I get the 5mm hose and that won't be a possible source of problem anymore. Jim told me to make sure that I use 7mm and 5 mm hose for the system and not 1/4'' and 5/16'' hose so I will follow what the professional says.
Thanks for all the suggestions and the help.
It sure helped me with all my thinkering on how to fix it.
Pinzgauer Pete if you have any question next week when you do the same as I did this week it will be a pleasure to help you as much as I can. I like to see people happy with their Pinz as much as I do.
Now back to another trip.
Denis