Craftsman 6-24 snowblower

I've recently acquired a 1978 Craftsman 6-24 snowblower (model # C459 528540) with a Tecumseh Engine (Model 143686162  Ser # 8155D)   The old blower is in remarkable shape, sat inside for years. 
The fuel was stale, tank dirty. I removed the tank and entire fuel line from tank to carburetor. Cleaned the tank, replaced the fuel line, Changed engine oil, fresh fuel (Stabil), new spark plug, lubed everything I could see.   
Got the unit running.
A little tricky to start, runs, but not smoothly. Have tried adjusting the carb, but still cannot smooth it out entirely.
The running engine does not smoke, doesn't seem to use oil, but doesn't seem to be able to rev up and respond to increasing workload...? Running it into larger snowdrifts tends to stall the engine. It simply doesn't have enough power.
Where might I be able to find a users manual or other specifications....?
Any thoughts, or advice...?
 
Bruce Macd.....

Thank you for your response, Roy.
That's  precisely what it acts like. Like the governor isn't doing it's intended job. I'll have to check that function.
 
The carburetor and linkage/governor connection is hidden under a metal shroud and not readily observable.
I'll need to remove the shroud and watch what happens at the carb when working the machine.
 
While cleaning and lubing the machine, I did notice a spring, (3" or so in length) that appeared to be stretched and loose. That spring was connected somehow in the linkage in what I believe to be the governor control system...?
 
When getting the machine running, initially, I seem to recall seeing some movement in what I think may be a governor connection protruding out between the cooling fins on the front of the engine block.
 
Any idea what the HP rating of that old engine might be...? Any advice will really be appreciated.
This is all kinda' new to me.
Bruce