Spark Advance Snap-back Check ?

Have a 1984 120 Merc. When I rotate the rotor and let it snap back (to check the spark advance mechanism under the distributor) it snaps only most of the way back. It seems to not completely return to the original position. Is this OK? Engine has a surge at WOT only.

Re: Spark Advance Snap-back Check ?

Sounds like weak CA springs. I can hardly manual rotate my distrib rotor/shaft without removing the point plate and assisting by pushing on the slotted bars. The advance wants to be actuated by centrifugal force not by manually turning the shafts. It is true that the springs should be weakest at the lower end but they should pull back to start, with no rotation unless they are simply hanging up. (rusted/corroded etc.)<br /><br />It would seem to me if your springs were weak, it would let the distrib max out early but not dither back and forth at WOT, but maybe not.<br /><br />Best thing is to find a distrib guru in your area and have him test/inspect it on his distrib machine. They will also check for worn bushings.

Re: Spark Advance Snap-back Check ?

Check for a hard grease build up between the two halfs of the shaft and for rust(the most common fault). The springs will rust and weaken, the shafts will rust between the halfs and the weights will rust on the pivot pins.

Re: Spark Advance Snap-back Check ?

OK, thanks guys. I am interested to see this "distributor machine".