If your dock is normal strength ? You can do all the idle in forward gear while tied to the dock. Up to a very fast idle should be no problem for the dock. After reliable dock loading tests. I take a boat out on the water for higher power testing.
The compression reducer is normally only functioning during very low engine speeds. Such as rope hand starts.
I went to JLM site and read a detailed parts list. Could not find any words like compression release. About any parts.
So we really do not know if it is really the original carburetor for that year ? How do we determine what model that carburetor is with out some identification numbers ?
Seafoam is a SLOW acting solvent. It does not suddenly dissolve all the crud at once and block tiny fuel passages.
I use it 1 time about each year to regain the lost mileage do to crummier modern gasoline.