Small Engines (Lawn Mowers, etc.): Tecumseh 4hp

Question
My Toro 21" walk behind mower w/ Tecumseh 4hp dies off at high rpms and lacks power to run at any speed.  I discovered oil at the top of dipstick/also oil spatters out when it is run with the fill cap off.  Suspect rings or valves not seating?  Good old mower, but . . .  
If engine replacement is recommended, can you give me cost estimate?

Answer
Engine prices vary for some Toro mowers but you may be able to find a new engine from $140-300.

As for your current engine, oil will splatter out with the carb removed...normal.

If I were you I would do the following:

Drain the old oil
Check the dipstick tube o-ring, I'd replace as these wear and can cause a leak
Clean the valve breather.  You will probably have to remove the flywheel to remove the breather.
Check the head bolt torque...seen these loosen on Tecumseh engines.
Refill with new SAE-30 oil.

Test operation.

On of the URL's should be your engine repair manual:

http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_L-Head_E

http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_4-Cycle_

If neither are the service manual for your engine, send me the Toro 5 digit model number and the engine model, spec and serial number so I can look up the manual.

Eric