93 Mercury SportJet 90 Fuel Consumption

[d.andolsen]

I have read through the correspondence associated with the Mercury Sportjet 90. <br />Although I have experienced the dreaded "black stator" and "rev limiter" problems, my question relates to performance and fuel consumption.<br /><br />My Sportjet 90 reaches a top speed of about 25 mph and consumes an enormous 8 gallon per hour. Based on information from the Clymer Shop Manual my inclination is to begin looking at the Fuel Recirculation system. Does anyone have experience correcting a problem of this nature ?

 

[SB]

Re: 93 Mercury SportJet 90 Fuel Consumption

My 94 Bayliner Reflexx Sport Jet 90 has a top speed of 35 and uses about 10 gph. It uses less if I keep it at a lower speed. I don't really have a way to track comsumption except seeing how much it takes when I fill up. I do use a gps for speed however.<br /><br />From what I have heard these numbers are normal.<br /><br />Scott

 

[d.andolsen]

Re: 93 Mercury SportJet 90 Fuel Consumption

SB. Thank-you for the reply. It seems 8 gph is to be expected with this engine. I also saw your comment from another posting of 1 gal/hr per 10HP. So it adds up.<br /><br />Any ideas on the 25 MPH performance at WOT. Would you suggest that I not focus on the Fuel Recirculation and focus on other items such as fuel pump rebuild, ride plate adjustment, carb. rebuild or jet drive rebuild.

 

[SB]

Re: 93 Mercury SportJet 90 Fuel Consumption

I won't pretend to be an expert on these but I have been playing with mine for a year.<br /><br />First of all are you sure that it is only going 25. My speedometer is very inaccurate so I use an inexpensive GPS. The next step is to determine if the engine is reving properly. Mine doesn't have a tach so I just ordered one and will be replacing the speedometer with it. If you are attaining the WOT rpms then I would look at the ride plate. Not so much for adjustment but for leakage. This will really slow the boat down.<br /><br />If you aren't getting to WOT rpm, about 4700-5300, then start checking the engine.<br /><br />One thing that I did to mine is I added Nauticus trim tabs. Before I put these on it would porpoise badly. These solved that problem and made the boat handle much better. It also dropped about 2 or 3 mph from my top end since they do add a little drag, but they are worth it.<br /><br />By the way, what kind of a boat do you have? I figure that mine weighs about 1400 lbs with two people.<br /><br />Scott

 

[d.andolsen]

Re: 93 Mercury SportJet 90 Fuel Consumption

SB. My boat is a 13.5' - 93 SeaRayder. I really like the style and size of the boat. It is perfect for my small family. As with your boat I do not have a tach so I am not sure of my RPM's. The speedometer came stock with the boat so I am also not sure of its accuracy. Therefore I am shooting in the dark.<br /><br />I guess my first step as you mentioned should be to install a tach. Thanks for your advise.