I have a Johnson 25e74m outboard, which came with an old 14 ft Hourston boat and trailer. My problem is when I set pistons on motor at TDC the set mark on drive shaft cam is well past TDC and piston is on the down stroke, can't retard the magneto plate to align marks as the brass stop is against the shift lever which also works the start safety switch. Consequently when trying to start it just backfires. I should mention motor has 120psi on both cylinders and strong spark also cleaned carburetor. Thanks in advance for any suggestions.