Oy, I'm such a noob. Took me a week to get a new inductive pickup for my tachometer, the old one died as I was starting to check the mower out. Turns out I was running at under 2900 RPM. Adjusted the throttle up to 3300, and lookin' good. Jeez.
The Harbor Freight automotive super-multimeter is an awesome tool and very reliable except the inductive pickup broke after 7 years and can't be replaced separately. So I'm out another $35 to replace the whole thing, minus whatever I get for selling the old unit on craigslist. Annoying, but $5/year is acceptable.
The other problem is that the inductive pickup is too bulky for small engine work; I had to remove the engine cover (translate starter reel and fuel tank) just to read the RPMs. LCD Automotive Multimeter with Tachometer Kit