1982 mercury 9.8 only 6mph!!!

[saabsaviorlee]

Hey guys I graduated from my sevylor fish hunter 280 into a 12.5' wood floored inflatable dinghy from newport vessels. Took her on the maiden voyage to lake pleasant in az with an 82 mercury 9.8 it was myself, a buddy, cooler, 6 gallons of gas, 1 marine deep cycle battery, 30#minn kota, and assorted fishing gear total weight including passengers inside the boat would be around 700lbs. GPS clocked us at 6.2 mph does this speed sound normal? I had the motor serviced before the trip with new plugs fluids and overall bill of good health. Should I be getting faster speeds? Does octane affect speed in this 2 stroke motor? The prop pitch is 7" with a 8.25" diameter. Would upping the pitch be wise given the weight load? Ive seen countless videos of similar setups reaching speeds of at least 10-14 mph. Any advice would be appreciated!

 

[hystat]

that's a fair load, I suspect you might want to go down in pitch rather than up - but check what rpm you are achieving. prop the motor to achieve recommended WOT rpm (I would guess 5500, but consult specs)
You can get a simple tach on ebay that just has a wire that wraps around 1 spark plug to check rpm.

does it go well with just you and no passengers/gear?
the motor may be firing on 1 cyl. or otherwise not tuned correctly.

 

[guyjg]

What did you expect w/an elephant on a skateboard?