low rpm at full throttle on mercury 115 hp

[zeus7888]

at full throttle i am only running 2200 rpm,i have a 1976 mercury outboard,with a 1980 power head,i have changed the switch box with a new one,rebuilt the carb.s,checked the coil,and distributer,it starts very good,runs great,but when i go full throttle,it only gets up to 2200 rmp,planes out good,could it be faulty rmp gauge???speed gauge show running 25 to 28 mph.
Thanks for any help i can get

 

[Chris1956]

Re: low rpm at full throttle on mercury 115 hp

It sounds very much like the Tach is incorrect. 2200 RPM won't get you on plane.

What kind of boat and what prop pitch are you using? Your speed is reasonable if you have a heavy boat or too large of a pitch on the prop.

 

[zeus7888]

Re: low rpm at full throttle on mercury 115 hp

i have a 21 pitch prop,and the boat is a 1976 sea charmer,that i rebuilt from the hull up,it is much heavier now that it was,new ribs and more flowtation

 

[verado7]

Re: low rpm at full throttle on mercury 115 hp

sounds like the tach is faulty - 28mph sounds reasonable on a boat of that size - theres no-way you would be doing that speed with only 2200 rpm

 

[zeus7888]

Re: low rpm at full throttle on mercury 115 hp

thank you for the help,i think i will change the rpm gauge and see what happens,thanks again

 

[Droll]

Re: low rpm at full throttle on mercury 115 hp

i have a 21 pitch prop,and the boat is a 1976 sea charmer,that i rebuilt from the hull up,it is much heavier now that it was,new ribs and more flowtation

Don't know your boat but a 21 pitch propeller sound a bit big for a inline , unless it's a very light boat ..

Had to go down to a 17 pitch propeller on my boat to get the WOT rpms up to spec. ( relatively light 15 foot boat ( a 60s hull design ) with a early eighties 90hp ported to 140 spec ( 1972 140hp ) ) .


Arne Kjetil