In early June there were several postings about engine dying problems. Recently I've had engine problems in my 149 and I thought I would share my experience. The K321 would run for about 15 minutes then surge/hunt. Closing the choke slightly would help for awhile, but a few minutes later the engine would die. After a few minutes I could restart the engine, continue mowing, but the surge/hunt and stall repeated.
So this seemed a good time to tune-up the engine. I decarbed the head and valves, put in new points, Kirk's PointSaver and Bosch coil, coil wire, Autolite spark plug, and new gaskets. In the past 18 months I had replaced the fuel filter and rebuilt the carb with the carb kit, so I didn't touch those.
After all that I still had the surge/hunt and stall problem. In hindsight I should have simply turned out the high idle fuel needle, but no, I do things the hard way. I noticed some looseness in the carb throttle shaft. But the Cub FAQ suggests a little looseness in a Kohler throttle shaft isn't always a problem, though I didn’t try the temp grease plug trick. I had also read of a relatively easy fix that didn’t involve drilling out and replacing the bronze bushing. I removed the throttle shaft, applied some JB Weld inside the bronze throttle shaft bushing, and temporarily reinstalled the throttle shaft. After two hours I removed the throttle shaft and cleaned it. I let the JB Weld harden in the bushing. The next day I installed the throttle shaft and the looseness/slack was gone. Of course the day earlier while removing the throttle lever, that tiny #2-56 x 7/32” screw sheared off. So I drilled out the screw and peened into the throttle shaft screw hole some copper wire which I wrapped around the lever. I haven’t yet gone to a hobby shop to find a replacement screw.
So I’m now ready to adjust the carb fuel needles and idle speed. I turned in the needles to seat them, and stupidly forgot to check how many turns it took. I backed out both to Kohler’s Preliminary Settings. I then noticed the main/high fuel needle screw head seemed much higher than before because some clean screw threads were now revealed. Hmmm…I wonder if the Cub Cadet shop that rebuilt my K321 in 1999 only turned out this screw 2 turns (for a K301) instead of the 3 ¼ turns for a K321 and I’ve been running lean all these years?
The cub started right up, and at most engine speeds the governor arm is nice and steady with no surging/hunting. I adjusted the two fuel needles in/out per the manual to find the optimum position, but it seems the preliminary settings were just about the best spot. I’ve got a TinyTach on the 149 which helps a lot in checking engine speed. Adjusting the idle speed screw has been a bit frustrating. At times it runs at 1200 RPM, which is perfect. Other times it is at 1050 or as high as 1400. I haven’t yet figured this out – the screw tip, and not the bevel, is touching the throttle lever – so that seems okay. I do notice that at 1200 RPM the engine and frame shakes and twists, but at 1350 it purrs rock steady. The manual says 3600 RPM is the max engine speed and I’m running at 3340 RPM with the engine under load, ie with the 42” deck running. I can get the speed slightly higher with the throttle all the way up, but then I get some surging/hunting.