New Vanguard starter only spins slowly even when

I had one year old 18-hp Vanguard suddenly develop the problem of starter not spinning engine fast enough to start. ( This happened after it had just successfuly started the engine at a temperature of 18-degrees F.) After trying 3 x known to be good starters that all showed heavy current draw and would not spin the engine-- I checked the valve lash and found it to be in tolerence.

I tried assisting the starter with my Milwaukee Hole-Hawg drill, (the one with the WARNING-NOT FOR STARTING ENGINES!), to no avail. A Briggs mechanic said to remove the plugs and see if the engine will spin easily. "No spark plugs = no compression = Who cares what the valve lash is. My engine is shaft connected to Hydrostat Tranny in a John Deere 318. Engine did not turn freely with no sparkplugs. Mechanic said something internal was hanging and to try flushing engine by draining oil and adding two quarts of Diesel fuel to crankcase. I did this and motored the engine by spinning it with another engine through the electric clutch belt pulley. After 5 minutes of this treatment, I replaced the sparkplugs and tried cranking with the starter. The engine immediately started. I quickly shut it down, drained out the Diesel fuel from the crankcase, changed the oil filter, and added new oil, Mobil-1. The engine continues to start and run "normally" for the past 5-months on snow removal and lawnmowing. This worked for me without having to tear down the engine . I have no idea what the hang-up was but a Diesel fuel enima made the problem go away. I had one year old 18-hp Vanguard suddenly develop the problem of starter not spinning engine fast enough to start. ( This happened after it had just successfuly started the engine at a temperature of 18-degrees F.) After trying 3 x known to be good starters that all showed heavy current draw and would not spin the engine-- I checked the valve lash and found it to be in tolerence. I tried assisting the starter with my Milwaukee Hole-Hawg drill, (the one with the WARNING-NOT FOR STARTING ENGINES!), to no avail. A Briggs mechanic said to remove the plugs and see if the engine will spin easily. "No spark plugs = no compression = Who cares what the valve lash is. My engine is shaft connected to Hydrostat Tranny in a John Deere 318. Engine did not turn freely with no sparkplugs. Mechanic said something internal was hanging and to try flushing engine by draining oil and adding two quarts of Diesel fuel to crankcase. I did this and motored the engine by spinning it with another engine through the electric clutch belt pulley. After 5 minutes of this treatment, I replaced the sparkplugs and tried cranking with the starter. The engine immediately started. I quickly shut it down, drained out the Diesel fuel from the crankcase, changed the oil filter, and added new oil, Mobil-1. The engine continues to start and run "normally" for the past 5-months on snow removal and lawnmowing. This worked for me without having to tear down the engine . I have no idea what the hang-up was but a Diesel fuel enima made the problem go away.