Warning: this engine may have a fixed-speed carburetor, which is NOT the same thing as a manual-throttle carb.
Back story.........
I bought a new mower a couple months back and decided that I wanted to put a manual-control throttle on the old one so that I didn't have to run it at full-RPMs all the time. When I asked about adding a manual throttle linkage at the local old-time hardware store, the guys there said that I'd need to get a full-range carb (assuming one was even available that would fit) because the single-speed carbs on most mowers now will not control the engine over its entire possible speed range.
They did not have the info to find out what manual carb would fit, and suggested I go to a dealer for that engine line--which is a Techumseh, so I gave up that route. The mower is ~9 years old and only cost $140 new so I felt it was not worth buying a new carb for.
I went home and just for fun, tried disconnecting the automatic throttle linkage and putting a "manual" throttle on (a pair of small vise-grips on the butterfly control arm) and sure enough what they said was true. Even under no load and the butterfly held open the engine would only turn slightly faster than it's "target" RPMs, and closing the butterfly all the way still left the engine running at around 50% of its target speed.
If you are shopping for a utility engine for motor-bike use, then you want one that has a "manual" or "full-range" throttle, elsewise you will need to get the right carb. If you look around at anyplace that sells small engines online you can see this: horizontal-shaft go-kart and minibike engines always have manual throttle carbs, but almost all vertical shaft <7hp engines now only come with automatic throttles.
...And the Harbor Freight pump engine specifies 6500 RPMs in the specs, which would lead me to believe it's got a single-speed carb.
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