Performance increase expected

[Sprint 277]

150 Mariner Mag 3 shaving heads to 34cc and adding carson reeds. What performance increase can expect and will I need to increase jetting on carb

[JohnG]

In wrong section

[whipper]

You might notice better take off and mid range. Not to much after that. The lighter the boat the more you'll notice it. To take advantage of more compression with tighter heads you need to let her eat fuel! Tighter heads like increased fuel delivery. To get even more ya need to add more air to the equation also. The combination of air and more fuel you will feel at mid range up. Its a little tricky doing this manually. You have to take a run let off {cut} the throttle then go pull the plugs and see if your lean or rich. You want them just tanned not black and wet or partially light tan or burnt looking. Just a nice even tanned. WOT is were you need to check this hence chopping the gas. thats were you should be the leanest. So if ya let her slow down and still running you wont get a true read as the richer lower rpm would have darkened the plugs.
Just bring your tools and a couple sets of NEW plugs on a very calm day with no other boats around and test all afternoon. You should get it in about 4 or 5 passes. Really try and feel and think about what your going for. it then will be worth it. once you get the colour you want you can forget about it and boat with confidence that you tested.