Mechanical slide carbs rely on differential pressure to push fuel through the fuel jets. The differential is provided by the partial vacuum produced by the falling pistons making it's way to the carb throat, whereby the atmospheric pressure at the top of the vented float bowl exerts force on the fuel pushing through the jets and into the carb throat to be mixed with the air from the intake.
Raising the slide, allows outside atmospheric pressure to flood the carb throat, drasticly changing the differential pressure the carb relies on to operate, either stopping the fuel jet flow or severely reducing it. Lots of air, and minimal fuel results in no power from the engine. I.E. "bog". I call it wheeze, as I use bog to pertain to an over rich condition with associated "burble" during operational recovery. "Wheeze" recovery resumes operation cleanly.
It is unreasonable expect a mechanical slide carb to operate well from whacking the slides fully open suddenly. The physics do not support its continued operation. Unless...
The idle mixture is ridiculously over rich, likely fouling plugs during prolonged idle (and getting very poor fuel mileage). Or, an accelerator pump is included to squirt raw fuel into the carb throat when the slide is suddenly opened.
All my 550's (same carb arrangement) exhibit this bogging/wheezing behavior (as they did when brand new). All my 750's with their mechanical slide carbs have accelerator pumps (77-78). They don't bog or wheeze whatever you do to the throttle.
CV carbs have a vacuum operated slide that prevents the operator from suddenly opening to both ends of the carb throat. So, they generally don't need an accelerator pump. The EPA likes these as they emit less unburned hydrocarbons into the exhaust.
Cheers,
