I am the proud owner of a beautiful 1974 Ford P350 Van Ice Cream Truck / Step Van. It has a straight 6 300 4.9L and a single barrel carburetor with an automatic choke. We have replaced a lot of parts (new alternator, rebuilt carburetor, ignition coil, distributor cap, rotor, wires, spark plugs, fuel pump, fuel filter, transmission gaskets/seals, motor mounts, transmission mounts, thermostat, break booster check valve, gas cap, radiator cap and exhaust manifold). The carburetor is hooked up a little weird. The intake manifold carb mounting area has the one large hole and then a small hole next to it. There is a gasket and then a piece of thick sheet metal on top of it which covers the small hole and then another gasket and then the carburetor. When I search carburetor gaskets for the truck, they all have just the one big hole? So anyway, it runs great until you get off of the highway and then it wants to stall at the first light that you stop at. When I arrive at places after a longer drive, it’s hard to keep it running. It will also often stall when warm and you shift into reverse or drive. Short drives are no problem.
When it stalls, you sometimes have to hold the gas pedal down to restart it. It was running hot and once after a highway trip on a warm day, coolant was “bubbling” into the overflow. I have since installed a fan shroud (since it didn’t have one) and now it seems to be running cooler. My mechanic used his IR thermometer and didn’t think that it was running hot, but it sure seems to heat up fast and get pretty hot. When it’s hot it also seems to be “idle hunting” and then sometimes stalls while its in park or neutral.
I have tried adjusting the idle screw and the fuel mixture on the carburetor. When it’s hot, I have to turn up the idle enough so that I am worried about damaging the transmission, so I have kept it lower. No matter what settings I try, I can’t find an acceptable setting.
I had my mechanic check for vacuum leaks and he said that he didn’t find any, however I tried spraying some starter fluid and found some problems. When I spray it at the base of the carburetor or at one spot on the intake manifold seal it immediately stalls. I thought that when you find a vacuum leak this way, the engine revs higher when you introduce fuel / richer mixture into the engine. It’s also really hard to tighten the carb mounting nuts.
I have thought about trying to get it running cooler with a new fan clutch or a new radiator. I have also thought about a thicker carb mount gasket or maybe 2 gaskets. I don’t know what the extra hole is in the intake manifold and if I even have the right carb mounted.
Any ideas or help would be greatly appreciated. My knowledge is limited, but I’m always learning. Anyone who helps and is near Albany, NY gets a free ice cream!