Google search results revealed these steps on another forum for a guy doing the exact same thing. Search terms 2005 Suzuki DF40 top dead center
Here is some text, but the other thread has pictures:
The service manual directs that "Before installing fuel pump, rotate the crankshaft to the number 1 (top cylinder) piston to Top Dead Center (TDC) on the compression stroke."... not exactly sure why but here the procedure I used.
Remove spark plugs... or else you cannot rotate the flywheel.
Exposing the flywheel is a simple matter of removing one screw (at the rear of the flywheel cover) and pulling up on the cover at both left and right sides to pull the two (left and right) rubber fasteners away from the motor.
With the cover removed, the "built-in" peep hole and indicator mark (that is part of the cover) is no longer able to be used, so I put a piece of masking tape near the front of the flywheel and marked it, to tell me when the No. 1 cylinder was nearing TDC. With some effort, (and with all four spark plugs removed) you can rotate the flywheel by hand... rotate it counterclockwise. While sneaking up on the "spot" and when I thought it was just about right, I temporarily placed the flywheel cover over the flywheel to verify with the "T" (stamped on the circumference of the flywheel to line up the flywheel) to insure the No. 1 cylinder was at TDC
Old-school method of verifying a particular cylinder is at TDC. Wooden dowel pushed into spark plug hole to rest against top of piston. As crankshaft is rotated, dowel will move in and out... when it's at it farthest "out" position, that cylinder is at TDC.
Hope this helps
