I guess this must be a carbureted 951 engine? If one carburetor is malfunctioning (dry) the associated cylinder won't receive fuel. If that's the case, that's not good for the cylinder b/c fuel is responsible for carrying lubricant through the engine. Thus, no fuel = lack of lubricant.
I would perform a compression test, but before starting the engine again though I would pour a few ounces of oil in the dry cylinder for lubrication in case there isn't enough lubricant on the cylinder walls. Hopefully you have at least 120psi of compression pressure/cylinder, a very healthy condition engine will produce around 130psi
If you want to verify there's a fueling problem of some sort, the best quick test involves mixing up an ~32:1 or so oil/fuel mixture and pour that in a squirt bottle such as a windex bottle. Start the engine and squirt the pre-mix directly into the offending carburetor while the engine is running as a fuel source for the dry cylinder. The fuel mixture provides something for the cylinder to burn, thus if the cylinder begins firing this confirms the carburetor isn't fueling (for whatever reason).
If the carburetors are "factory fresh" and have not been rebuilt by now, it's well past time. Also, the factory fuel lines should be replaced as well, especially the gray colored 1/4" ID lines made by Tempo, they corrode inside and will plug up the fine passages inside the carburetors.
While performing fuel system maintenance, the reserve/off switch valve should probably be replaced b/c as they age trash in the fuel collects inside the valve and the o-ring seals dry out.
