L135 Backfiring out Exhaust

[Rosher18]

Good afternoon everyone,

I was mowing my front yard yesterday evening and noticed as time went by that the frequency of muffled popping from my exhaust went from 0 to "rather often", meaning maybe 20 times in as many seconds. I haven't noticed a loss of power yet, but it sounds a lot like it's missing a spark rather frequently. The engine bay was very hot after I shut it down, which seems to support my notion that it's just dumping unburned fuel-air mix into the muffler, where it is burning. I tapped a small cloud of dust out of the air cleaner (which I clean after every use) but haven't had a chance to run it since then. I'm going to pull the plugs today after work and see if either of them show signs of improper combustion.

Has anyone else experienced this or fixed it? What did you do that fixed the problem?

Edit: It has around 340 hours on it, valve clearances adjusted within the past 5 hours of running.

 

[beenthere]

Have the engine cooling fins collected any debris, or mouse nest?
Just a thought...

 

[Rosher18]

Have the engine cooling fins collected any debris, or mouse nest?
Just a thought...

That's a good question. They're all covered with sheet metal. This was my father in law's but he gave it to us as a housewarming gift. We've only put about 20 hours on it since then. I always check the flywheel fan for grass bits when refueling, and if I can see into the cooling fins I'll check those.

 

[Yellowfever440]

The engine bay was warm? As in opening the hood it was warm? How are you judging that, I'm curious because I assume it's air cooled and the temperature under the hood would depend on the time of day and the outside air temp. If the valves were adjusted recently I would doubt check the jam nuts and make sure they are still adjusted properly.

 

[Rosher18]

The engine bay was warm? As in opening the hood it was warm? How are you judging that, I'm curious because I assume it's air cooled and the temperature under the hood would depend on the time of day and the outside air temp. If the valves were adjusted recently I would doubt check the jam nuts and make sure they are still adjusted properly.

Yeah, upon opening the hood it felt a lot hotter than I'm used to feeling when I've just shut it off. I was working it a bit harder than usual so it's possible the heat is a red herring, but the popping is definitely a newer issue to me.

I'll check the lock nuts on the rocker arms as well.