Have you checked for wear internally, between the lever arm and the starter drive? There should be little or no movement of the lever before the drive encounters spring pressure that is trying to disengage the drive gear from the flywheel. It only takes a tiny bit of slack anywhere in the linkage fron the foot pedal to the drive gear to start the motor spinning before the gear is engaged. Your idea of slotting the switch mounting holes might work, but untold thousands of these starters work right without requiring any modifications. Manufacturing tolerances can stack up wrong to make yours the exception! You could also have a replacement switch that's been assembled incorrectly by a 12 year old kid in a Chinese sweatshop. The malfunction I've encountered frequently is a switch that won't run the starting motor without slipping the screw top from a Coke bottle over the push button to make it engage sooner.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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