Many boat technicians will tell you to never mess with the timing on your outboard motor, but making timing adjustments on your Mercury 7.5 Hp Outboard Motor is relatively simple if you have a dial indicator. Timing adjustments should be made according to your regular maintenance schedule, when you're experiencing problems with your throttle and boat speed, and after you've replaced the timing belt.
Look over the instructions on timing adjustments in your owner's manual. Many of these instructions are much more complicated then they need to be, but the figures will help you to identify parts of the boat that you may be unfamiliar with.
Remove the cowling cover on the power head and take out the spark plugs. Locate the flywheel and timing belt.
Attach your dial indicator to the flywheel. You must have a dial indicator in order to properly adjust the timing. The dial indicator should be attached to the first spark plug hole. Turn the dial indicator to the 0 position in order to lock it into place.
Adjust the timing. Turn the flywheel counterclockwise until the dial indicator reads .550. Now turn the flywheel clockwise until the dial indicator reads .491.
Remove your tools and finish up. Remove the dial indicator from the flywheel and replace the spark plugs so they are secure. Place the cowling covering back on the power head and start your engine.
After adjusting the timing belt, you may want to adjust the timing on the ignition as well. The suggested number settings above are not arbitrary marks. You should follow these number specifications exactly, unless your owner's manual or an experienced technician tells you otherwise.