I was out mowing today with the 129, trying to bring under control about 12 days worth of fresh spring grass. I had freshly sharpened blades, so although I was working her a bit, she was handling it in stride for the first acre and a half of my slightly more than 2 acre lawn, but then it started to misfire, like it was starved for fuel. I confirmed it was a fuel system problem by pulling out the choke, which made it run temporarily better, and this let me nurse it back to the garage.
I suspected that something was plugging up the fuel system, so I disconnected the fuel line from the carburetor to see if fuel was making it past the petcock, which it was. I reattached the fuel line and pulled the bowl off of the carburetor, and fuel seemed to be coming out okay, so I put it all back together and after about 20 minutes more, it started starving for fuel again.
I decided to grab a beer and let it cool off for a while, and attacked the problem again, figuring that something was intermittently blocking off the fuel. I pulled the fuel bowl again, disconnected the fuel line, and shot compressed air back through the petcock valve, and made an attempt to back blow air through the needle valve area, but without removing the float, figuring I might dislodge something there.
Well, I put it all back together again, and it ran great for about 10 or 15 minutes, but started to die again. I was within 5 minutes of finishing up when it happened again. I pulled the fuel bowl, made sure there was gas in the tank, and added some extra in case, and repeated the previous drill. This time, it started to die after only a couple of minutes, so I decided to finish up with the Simplicity.
I still suspect a clogged jet or needle valve, but I also noticed a noise coming from the carburetor after the engine was shut off, similar to water boiling in a kettle. I might also guess vapor lock, but I've never had a problem like this before with the 129, or the 102 in all the years I've mowed with it.
I've called it a day for now, but I might pull the carburetor tomorrow and clean it out properly. Any guesses or things I might not have considered?