Working on a husqvarna 128c weed trimmer, which I understand has a catalyst in the muffler. It has probably less than an hour or two runtime, but sat for too long with fuel so the carb gummed up. I replaced the carb with an amazon Zama clone, and got it running decent, but it runs SO HOT. Like, the engine keeps running with the plug wire pulled hot. My understanding of tuning 2 strokes is to bias to the rich side. Traditionally with chainsaws, weed trimmers etc I will set the high speed mix by ear; with the throttle wide open I'll play with the high speed screw to find the highest RPM, and then richen until it just barely starts "four stroking", and leave the setting just barely leaner than that to make sure it has enough fuel to not melt down.
In this case, even running rich like that, the machine seems to overheat, which makes sense from the fact it has a catalyst that is burning up all the unburned fuel in the exhaust. How do I find the happy setting between piston melting lean, and catalyst/muffler melting rich? It seems to overheat, ping, and diesel instead of shutting off regardless of how I set it. Have done a few plug chops and the plug always has a nice chocolate color, but with shiny spots& nicks from pinging. I have a bad feeling this is just the nature of the machine...
In this case, even running rich like that, the machine seems to overheat, which makes sense from the fact it has a catalyst that is burning up all the unburned fuel in the exhaust. How do I find the happy setting between piston melting lean, and catalyst/muffler melting rich? It seems to overheat, ping, and diesel instead of shutting off regardless of how I set it. Have done a few plug chops and the plug always has a nice chocolate color, but with shiny spots& nicks from pinging. I have a bad feeling this is just the nature of the machine...