Poor low-end performance

[CSUGDEN]

I have a 91 Mercury 135 Outboard - Black Max and it has performed flawlessly up until last year when it started having problems attaining it wide-open throttle max rpm of 6600. Now it maxes out at 5500 and it crawls like a snail when I try to pull a skier out of the water.<br /><br />The carbs had some problems a couple of years back when it was laid up for a year but everything seemed to faill back into place. Now I have a rebuilt gearcase and am trying to resurrect the past great performance.<br /><br />Any ideas on how to recover the lost rpms?<br /><br />Charlie

 

[LubeDude]

Re: Poor low-end performance

Originally posted by Charlie Sugden:<br /> I have a 91 Mercury 135 Outboard - Black Max and it has performed flawlessly up until last year when it started having problems attaining it wide-open throttle max rpm of 6600.

Well, there will be more chime in on this eventually, but your max RPM is about 1,000 RPM too high. It is even possible you may have damaged something internally as you say "it started having trouble"! your max should be in the 5,500 RPM range. Give us some more information as to what prop you are running and are you sure you still have the same gear ratio in the lower unit, or is it the same one just rebuilt? Also, take a compression check and report back.

 

[CSUGDEN]

Re: Poor low-end performance

Originally posted by LubeDude:<br />

Originally posted by Charlie Sugden:<br /> I have a 91 Mercury 135 Outboard - Black Max and it has performed flawlessly up until last year when it started having problems attaining it wide-open throttle max rpm of 6600.

Well, there will be more chime in on this eventually, but your max RPM is about 1,000 RPM too high. It is even possible you may have damaged something internally as you say "it started having trouble"! your max should be in the 5,500 RPM range. Give us some more information as to what prop you are running and are you sure you still have the same gear ratio in the lower unit, or is it the same one just rebuilt? Also, take a compression check and report back.

 

[CSUGDEN]

Re: Poor low-end performance

Well maybe the tac was off but from day 1, 13 years ago that engine maxed out at 6600 rpm with a standard 17 pitch merc prop on it. The boat seller specifically asked me about the rpm back then and he saud that was where it was supossed to be. Never had any problem for 13 years till I bent the drive shaft (ever so slightly).