70hp merc only going 16mph

[russelleotero]

i have a 70 hp i just got back from the shop, i have never ran this motor so i wouldnt know how fast it went before, well, anyways i got this motor on my 67 glasspar tacoma boat which gross weight is only about 1400 with everything, the boat is a 16 footer fiberglass v hull, now, it gets wot and tops out at only 16 mph according to my gauge, and it takes a while to build to that speed, now i know this motor should be getting more speed then that, but is there a problem far beyond the propeler pitch, the motor is the inline 6 cyl. super marothon block.

 

[Bob_VT]

Re: 70hp merc only going 16mph

Was the motor always on that boat? Sounds like the trim could be set wrong or the motor was mounted too low too. Photos? What is indicating the speed? GPS or a vintage water/air pressure speedometer? Is the boat able to plane out?

 

[russelleotero]

Re: 70hp merc only going 16mph

the motor has always been there, and yes it is a water air press. style guage.

 

[russelleotero]

Re: 70hp merc only going 16mph

yeah, i am able to plane out the boat, but takes forever at full throttle.

 

[menditt]

Re: 70hp merc only going 16mph

possible problems i can think of are timing sync, fuel pump with low pressure, spun prop, float levels in carb not set right

do you have a tack, are you getting full throttle, if you are i'd guess its the prop spun,

anyway i hope you find out the problem as they are really frustrating at time,

Later
Menditt,