Small Engines (Lawn Mowers, etc.): Tecumseh Engine, friends and neighbors, throttle plate

Question
Hi Marc,
   I also fix lawnmowers for friends and neighbors as a pastime. I've got two 3 1/2 hp Tecumseh mowers like this. They will start after pushing the primer bulb about five times, but refuse to stay running unless I hold my hand partially blocking the carb. I've cleaned out the carbs and set the float levels properly. Have also replaced both intake gaskets. Checked for vaccum leaks. Compression is ok, spark is good. Got anything ?
                           Thanks,
                                  Mark

Answer
If you can keep them running by holding your hand partially over the carburetor inlet, this indicates there is still a blockage inside the carb.  When you "choke" the carb with your hand, you are affecting where the low pressure occurs inside the carb because the restriction is no longer the throttle plate or the venturi but your hand.  This will allow the fuel to be drawn from all available passages in the carb and give the engine enough fuel to run.  Hope this helps.