Small Engines (Lawn Mowers, etc.): muffler glowes red

Question
QUESTION: I have a Tecumseh HM100 on a generator that runs on 1/4 choke, muffler glowes red, runs rough, Tried opening main jet slightly, small help. Replaced both valves, lapped in at .009 and.010. Engine starts easy but backfires. Runs a while then dies. Have not pulled flywheel because of easy starting, steel half moon key. Am at a loss as what to do next.

ANSWER: Sounds like it is running lean.  Have you dis-assembled and cleaned the carburetor with compressed air from an air compressor and good quality spray can carburetor cleaner?

How old is the engine?  Does is have points?

Eric

---------- FOLLOW-UP ----------

QUESTION: Engine spec no. 159463R near the end of the list, no points. I have not ben able to determine why it is running lean. I cleaned the carb before I did the valves. Used fresh gas.

Answer
Copied from the repair manual:

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.

How long have you had the engine?  
Did is just start running hot all of a sudden?
What spark plug are you using?  
Are you sure the intake gaskets are sealing and they are the correct size?  I once had a customer use too small of a gasket on the intake and caused many weird problems...cut a larger hole in the gasket to match the intake hole and it ran great.

Have you considered replacing the carb?  Carburetor, Tecumseh 640260B, $15.88 on Ebay.

Eric