g_monk

Thanks Jonathan and Jake

Yes the gas cap is venting OK

My experience with 11 small 4-cycle gasoline engine equipment types is that cylinder etc. has to be de-carbonized at least every two years.  Useage is roughly 100 hours per year.

I thought about replacing the ignitiion coil but lowest cost I could find was $44.  A replacement engine is ~$210 which sounds like a better investment on a five year old engine ... and it fixes the problem whatever it is.  May see if my parts house can reliably test the ignintion coil.

Have doubts that ignition coil is the problem because in many cases when the engine quits after about 5 or 10 minutes of operation and the engine is hot ... I can immediately restart it and it and often get another 5 or 10 minutes or even longer.  I can understand an ignition coil failing when it reaches some temperature but I cannot comprehend an immediate restart and continued run.

5 year old engine is on a lawn blower.  Ran AOK until a month ago. Decarbonize about every 1.5 years

Symptoms have been the same for the last 30 days.  Starts on 2nd or 3rd pull.  Occasionally when starting have to give it full choke and then unchoke and repeat. Also when that occurs it will not run at idle.  Eventually that clears up and it runs for 5 to 10 minutes, then starts missing and finally quits.  After a few minutes I am usally able to start it and it again runs fine -even though still hot - sometimes for longer than 10 minutes.

Decarbonized combustion chamber and around valves. Not much accumulation.  Valves appear to seat OK.  Installed new plug properly gapped. Ignition system is the newer type without condenser or points.  Spark tests OK just after it misses and quits.

Totally emptied the gas tank and refilled with brand new gasoline.  Same symptoms

To me it sounds like the carb needs a thorough cleaning OR one of the valves is not closing after the engine gets hot

What would any of you recommend next: (1) Clean carburetor, (2) Grind valves and check clearance, (3) Go for a rebuilt engine including fuel system