Mercury 70 to 90 hp upgrade

[jclay71]

I have a mid to late 80's 70hp Merc outboard SN 0C122050 that needs some work. I recently purchased it with a 19' Carolina Skiff that I plan to use as a work boat on a clam farm. The carbs are in bad shape so I purchased a set of WME-2XK carbs on ebay from a 2000 90hp in great shape. I need the most possible performance from this motor because I will be carrying heavy loads on a regular basis.

My goal here is to get as much hp out of this little motor without spending a fortune or adding weight. Comression is good at 135-140psi per cylinder so I think it may handle the larger carbs with a re-jet and improved breathing. Yes, I know bolting on another powerhead would be easier and possibly less expensive. I don't to do things the easy way. Here are my questions:

• I'm planning to install CCM reeds and I'm not sure if the reed cage is the same for the 70 and 90. The parts diagram description for the 90 has the word "Handle" in the description and I have no ideas what that means. Should I upgrade to the 90 style cage? Is there a difference?
• The exhaust tube for a 70 and 90 is a different part number so I'm assuming I need to upgrade that also. I'm having a hard time finding one so will a 115 model work without risking damage to the motor?
• Will porting or opening up any passages help?

Any help or cheap parts is appreciated,

John

[Fast Fred]

fiber reeds are a good idea, the rest, well them blind bores are not much for steppin up in power from what they are, it's just not there.