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

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?