where is the air fuel mixture screw located on the carb?

[yooper-yahmee]

As the subjtect states.  Mine is running really rich

[Underdog]

How did  the carb's setting change? That would be my first question.  Was the carb removed for service or inspection.  Any other work done that could have thrown the setting off?
Remember, setting the air/fuel mixture when it's 85 degress F will yeild a different air/fuel mixture than when the temps drop to 15 degrees F.  
I only bring this up because I once took my carb off and cleaned it and did not replace the gaskets.
The gaskets leaked just the tiniest bit of air and through everything out of whack.

Is this an 624 or and 826?  Plastic tank or metal tank version?

[yooper-yahmee]

It's a 1979 vinatge (metaL tank) got it for ten bucks and fixed it all up about $200 in parts.  Used it for a season.  we get abou 300" of snow.  It did the job but it runs rich as heck.  The plug is caked with carbon.

I looked at the parts break down and checked the descriptions.  It appears as thogh it is the small screw with spring on the upper left of the carb as you look at it form the side of the machine.  I adjusted it a bit and it seems to be the air fule screw.  Under the rich condition it was running at about 1.5 turns out.. I went to 2.25 turns to lean it up a bit.  We'll have to wait and see how she works when it's cold.

This thing was running so rich that it would strat in the winter without the choke and if you choked it it woul blow black smoke and stall.

[Underdog]

I think it may be prudent to drill a hole in the side of the air breather cover.  A hole just large enough to allow a thin long reach screwdriver to reach the air mixture screw in question.  On my 826 (plastic tank) I have to remove the air breather box from the carb to turn the screw. A real bother.
A small hole would allow access to the screw.

[trouts2]

With 2 1/2 turns instead of 1 1/2 you are going in the rich direction not lean.
The carb and throttle linkages on those stick often so your internal butterflys may
not be in position they should be.  It might be useful to remove and clean the carb, inspect the jets and operation of the linkages.  Look into the throat while hand moving them.