Originally Posted by Easyrider
I notice you work for Barrus- is it correct that you have to advance the ignition by 5 deg too, to get the extra power.
If you engine is currently adjusted to 20º, you won't have a full open throttle.
If you engine is already delivered to 25º just change the carb gasket by a 30 model (it's much air wider than restricted 25 gasket)
If your engine is adjusted to 20º, advance to 25º to full throttle, and see if the butterfly is at 180º, adjust by means of stopper. Will have the extra 5 HP at the end for better hole shot, carrying more weight, use on larger boat, etc.
So not to get mixt-up, don't know if all Mariners/Mercury/Tohatsu's 25's are being delivered worldwide to 20º/25º, a matter to check out on each one's individual engine. All cowl 30's are delivered to 25º.
Note: this info is on the 25/30, 2 strokes tech service manual.