Small Engines (Lawn Mowers, etc.): Troy Bilt Junior Tiller, tecumseh engine, excess load

Question
My tiller runs Ok at low speeds but if I try to run at a high speed the engine gets
hot and seizes up. When this happends you can not pull start it untill the engine
cools down then it runs ok again. It has a new carb. and the oil is full. This tiller
is 20 years old but is not used for more than 2 hours a year.
Engine # H35-45572N  s/n 2237B Tecumseh engine

Answer
Have you checked the valves and removed the engine shroud to make sure the engine cooling fins and flywheel are not clogged with debris?

Hot running is not very common unless the engine is running too lean, not getting enough fuel, or the cooling system is clogges with drebris.

The link below is the repair manual for your engine:

http://www.cpdonline.com/692509.pdf

ENGINE OVERHEATS
1. Make sure the engine is not being overloaded. Remove excess load (sharpen blades, limit operation speed, process less material).
2. Check the oil level and viscosity. Add or replace as necessary.
3. Check for clogged cooling fins or obstructions to the air flow. Remove the blower housing, clean and reinstall.
4. Check the carburetor for correct adjustment or remove and clean the carburetor using tag wire and compressed air. See Chapter 3 under "Service."
5. Check the engine R.P.M. setting using a vibratach or other tachometer and compare it to the R.P.M. settings found on microfiche card #30 according to the engine model and specification number. Adjust as necessary.
6. Make sure the correct spark plug is being used. Check the ignition timing. See Chapter 8 "Ignition - Service."
Correct flywheel key or partially sheared key.
7. Remove the cylinder head to check for excessive carbon buildup. Clean as necessary.

Take off the engine shroud and let me know what you find.  Also, let me know what spark plug is in the engine?

Eric