Hi
Been through this but not with M37. Couple questions what is the air temp when this problem happens? Is it cool and damp? Is the manifold heat riser stuck?
Quick check to see if this is the problem cover the radiator bring the truck up to temp with the grill covered then take it for a short ride. Does the problem occure?
OK what was the problem when this was happening to me, fall cool damp, vehicle would stumble like no fuel stop open the hood check carb, clear fuel filter and look down the carb could not find the problem. Yes there was frost around the outside of throttle. Went through this several times until I had the problem, stopped removed the aircleaner look down the throttle throat with the throttle held open (engine off) could see ice in the throat.
Figured the ice was forming because of the ventury effect cooling the flow below 32 even thought the outside temp was well above freezing. Once I saw the ice started checking the manifold heat riser and repositioned the air intake tube to take warmer air. Problem went away.
Please let us know what you find.
Cheers Phil
