I recently rebuilt the carb on my son's LT-A50. There wasn't anything wrong with it, indeed it ran great, but not knowing the maintenance history I figured winter was a good time to do some basic stuff including a carb rebuild.

As it turned out, the carb was nice and clean with no deposits. I cleaned the needle and jets, reinstalled, and the engine started after a few pulls.

However, since then the engine hasn't been as easy to start as before the rebuild. A dead-cold first start of the day usually started on the second pull. Now it was more like 8-10 pulls. And once idling during warm up, the engine had a tendency to stall and require restarting. I played with the carb settings but could not tune out this change in behavior.

Finally, last week I picked up a clip-on tachometer. (Side note: Try to find one these days. They're almost gone. No auto parts store had them, including NAPA. A specialty auto tool store offered to order one for $200+ but warned it would take a couple of weeks since "there is no demand for them anymore". ?!?) I clipped it around the spark plug wire, started the engine, and voila - the idle was set to about half what was recommended in the service manual! I had set it by "what sounded right" and by how much the clutch was trying to engage. I had it at about 900 RPM, but the manual specifies 1800. I adjusted the idle screw, tuned the air screw to accommodate that change, and no more stalling out.

The next morning, I tried starting the engine from dead cold. It started on the second pull, just like before. Problem solved.

Moral of the story: Use instruments, not guesswork!