As stated, it sounds like it is starving for fuel, any restriction in the fuel line could cause that. Float in carb set a bit low, fuel pump startign to go, clogged filter, or, assuming the fuel line routing is similar to my 55 and 58, make sure the flexible fuel line from the tank through the floor of the cab is not getting real old and collapsing or swelling shut. I cleaned the tank and lines on my 55 recently and filled it with some fresh gas. (had been sitting for 3-4 years before I got it). It fired up and ran fine but after sitting with new gas in it for a couple weeks, it swelled shut and would not run. If I let it sit overnight, it wold dribble enough gas through that I could start it and it would run for a bit.... then die.