I just bought a 86 C10 with dual fuel tanks & a 305. It ran great however it did have a little (2-3 second) engine ping when taking off or goosing the throttle in park or in gear. This is a machanical fuel pump style, not electric fuel pumps in each tank. I was told the fuel selector switch was bad and you could not switch over the tanks and it was using the passenger (right) side tank. I got it home and with the key on/engine off I hit the switch on the dash to switch it over to the left tank. I heard the valve "move". It only made noise for a split second, maybe two. In the past any dual tank chevy valve (86 and older) the valve would open/close for several seconds (5 sec or more-usually) The gauge went to full and I monitored both tank levels to verify it actually switched over to the left and was drawing from there as well. By the time the left gauge was reading half full the engine developed a dead miss. I put new Champion plugs & wires in it as well as a distributor cap & rotor--no change miss is still there. I replaced the thermostat and adjusted the timing to 4 degrees as recommended. Engine runs great at idle, however when you put it in gear it was severely under powered and didn't run very good. I don't have very good throttle response after 1/4 throttle. If I floor it , it just looses power or very very slowly builds speed and takes forever to gain 3-5 mph. Meanwhile the "choke" light on the dash is lit up and stays on. I can adjust the timing and get it running good for highway speeds but it suffers on the low end, and vice versa. When I do this the miss goes away except when the timing is close to where it should be then it returns. I have replaced the fuel filter and the fuel pump, with no results/improvements. Is it possible that the fuel tank valve is not opened all the way for one tank or the other? I did not have this problem prior to switching the tanks. Truck is in great shape and tanks look brand new so I don't have any leaks anywhere on the fuel tanks. Is it possible that the crappy almost 1 year old fuel caused a problem withthe carb. The carb has the 2 wire connector at the top right side of the carb. Any help or info would be greatly appreciated.