I bought a handfull of 14 mm open ends at the pawn shop for a buck each. I have adjusted the valves about 15 times without any problems. Most pawn shops have a large inventory of tools, at low prices.

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82 300d 194
75 240d sold
Gulfstar 41 4-107 Perkins Westerbeke 4.4 Gen
Puegot Bicycle Legs
AYP Lawn Tractor Briggs 12.5