In Reply to: TSX 251 carb? posted by Rusty 2N on March 05, 2018 at 19:57:30:
"I can adjust idle with the power screw,"
If so, it ain't idling. If the power screw does anything, it's turning faster than idle and running on the main mixture.
These engines don't accelerate without hesitation. There is no accelerator pump to compensate for the throttle being opened quickly. Properly tuned, the engine will idle with a mixture that is almost too rich. That borderline too rich idle setting allows the engine RPM to increase smoothly as the hand throttle is opened at a normal rate. Yank the throttle open, or "blip" a foot throttle, and these engines will take a second or two to catch-up.