I have a Sherwin Williams Powerwasher with one of the above Tecumseh engines, (cant find a model number on engine. Operator manuel is for a OHH550 and OHH55, which is running very rich. I would like to know how to adjust the carb. to eliminate backfire and plug fowling from black soot. Thanks RMC

RMC, you can download the Tecumseh service manual for OHV engines which covers the ohh50 here:

http://www.cpdonline.com/695244a.pdf

Give it a 'look-see' and then if you have any questions, post them back here!