Hey guys, first post long time member be easy on me. I have a 18HP Go Devil Surface Drive and stock I have got some decent performance out of it. I have it on a 15ftx40" boat.
Can someone tell me a little more about decking my heads? Is this just milling my heads down for more compression? What about installing heads from a 24HP Vanguard, what can I achieve out of that? I have a 34 Mikuni carb off a old polaris atv, can I use this on my 18? I have read about a few others that have swapped out to Mikuni carb but do i need to modify or change my intake manifold? I am kind of clueless on these 18's, I have found plenty of info on mods for larger engines but not the small. Please give me some input so I can start getting this in shape before big duck season.

Here are some of my performance numbers bone stock.

8" or less water with just me, 27mph.
deep water with just me, 24 mph.

8" of water 2 guys aboard, 22-24 mph
deep water 2 guys aboard 21-23 mph
deep water 2 guys aboard, heavy load for fishing, up current 18mph.

3 guys on board in shallow or deep water and I struggle to get on plane, sometimes I can and reach about 15mph.

4 guys in boat and I am definitely not getting on plane.

I know alot of guys will say there is no way I am getting 27 mph out of a 18hp GDSD, but I am, no reason to bullsh*t, light boat, light load, shallow water, I weigh 160lbs.

I am not looking to make a 30+mph boat, I would like to put a total of 2 guys onboard, heavy load for hunting or fishing and reach a solid 25mph shallow or deep water.

No one?

How about this? Anyone know if the intake manifold from a 23 Vanguard will bolt straight to the 18? I see the 23 has a double barrel carb and intake, the 18 is single barrel. I am sure I could gain some performance and a much smoother running engine if those interchange..