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


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?


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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.

Copied from the repair manual:

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.


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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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