How important is having the correct spark timing on an outboard? My Merc 25 2-stroke with mechanical spark adjustment should be set to the 25 notch at 3500rpm and the 6 notch at idle. But currently- my idle spark at at notch 11. I hooked up a timing light to the motor and got that result. Adjusting the idle spark screw does nothing. 'Advancing' it by screwing in only raised it a few notches before not doing anything, and 'retarding' it by unscrewing the screw does absolutely nothing to the point where I can unscrew it to where it's not even touching the idle spark arm anymore. My carb is tuned correctly as per factory settings (1.25-1.75 turns out on air/fuel mixture screw) and idle screw is 'just touching' the idle plate with one additional turn in. My throttle linkages are also properly adjusted at 5.5 and 5.25 inches. The other linkage connecting to the spark arm is the timing link, which is NOT adjustable. Schematic for reference: http://www.boats.net/parts/search/Merc2/Mercury/25%20%282%20CYL.%29/0P325500%20%26%20Up/Throttle%20and%20Shift%20Linkage%28Tiller%20Handle%20Shift%29/parts.html The engine is currently running just fine at these stock settings, idling around 800rpm and fast idling around 1500 rpm. When I turn the throttle from 'start' into FWD or RVRSE the gears to do 'slam' and there is a smooth transition with just a nice light click when the gears engage. The only problem I can identify, is the little area where the idle spark adjustment screw contacts the idle spark arm is worn down and the plastic has an indentation in it. I ordered a new spark arm just in case. The engine works fine on the stand, but this issue is getting to me. Any additional ideas? I am using a cheap $35 timing light...do these read badly like a cheap compression tester?