2000-2005 Yamaha F40B Outboard Service Manual, Page 106Get this manual
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Measuring steps
(1) Turn the timing pulley to match "61" marking on the pulley with "6" marking on the cylinder block(2) Measure the intake valve and exhaust valve clearance on #1 cylinder(3) Turn the timing pulley for 120, and match "6" marking on the pulley with "6" marking on the cylinder block(4) Measure the intake valve and exhaust valve clearance on #3 cylinder(5) Repeat the aforementioned steps to measure the intake valve and exhaust valve clearance on #2 cylinder