Small Engines (Lawn Mowers, etc.): Tecumseh timing problem?, excess carbon, exhaust valve

Question
I have a HM 100 Tecumseh with points ignition that will start and run but it backfires through the muffler.  I took the head off and the exhaust valve slightly opens when it shouldn't.  I don't understand how to correctly time this engine, any help will be greatly appreciated.  Thanks Todd

Answer
Hi Todd,

Check if there is a wrong or fouled spark plug. Make sure it is properly gapped.

Make sure the carb is properly adjusted.

Valves should not be sticking or seating improperly.

Make sure the timing is set right.

Check to see if there is excess carbon build-up.

Improper Valve lash or Weak valve springs.

This should get you started anyhow.

Regards,

Howard