MERCURY SPORT JET 90 HP TOO SLOW

RICHRICH26

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Please someone help me. I have a bayliner jet jazz 90hp sportjet which will not go above 5 mph. Things I have done so far: Rebuilt carbs, compression 120-120-122, .032" clearance between impeller and housing, impeller looks great, new ride plate gasket, engine rpm's within spec. As you can see I have invested alot of money so far and any ideas no matter how small will be greatly appreciated. Thank you
 

Trent

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Have you checked the rev limiter?
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

No I have not checked the rev limiter the rpm's seem fine 4000 or better engine sounds and runs great seems like problem is in the jet prop
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

sorry something else I wanted to say is I am open for ANY suggestions
 

ODDD1

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Re: MERCURY SPORT JET 90 HP TOO SLOW

rich, if you actually have the impeller hooked to the motor [no gear failure] the only thing that will cause you to make rpm's and not move is air in the inlet water stream of the pump....exhaust gas or air ...it is getting in there and screwing things up....
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

about the air thing... it is my last resort, but with the ride plate gasket making a good seal i cant figure any other way of air getting in there. is .032" clearance satisfactory for impeller to housing??? is there any time of slip device on the impeller? i can turn the impeller and feel the compression strokes of the engine with no slop or play.
 

Terry H

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Rich...There is a spline on the shaft that can shear if impeller gets jammed. Check the spline and the lock washer on the nut...Make sure these are ok and make sure the nut is properly torqued. I think the torque specs call 18ft.lbs...Impeller clearance should be .020-.030, .032 should be fine.<br />just a Thought
 

muskiedaze

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Re: MERCURY SPORT JET 90 HP TOO SLOW

rich, one other possibility: is the reverse gate locking properly in the forward position? if it kicks back ya won't go. but my best guess is the key on the drive shaft is broken and the pieces can jam up and let you turn the motor.<br />john
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

About the spline on the impeller, I thought about that but the shaft is actually a threaded rod in which the impeller screws directly on the shaft so there is no option for slippage on that part the gate thing sounds like a possibility but the gate is staying up and out of the way of the nozzle. I am back to thinking possibly the drive plate gasket how well of a seal is needed??? Is there any other way for air/exhaust to enter the intake and cause the pump to cavitate???
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

The reverse gate needs to be up and out of the way of the nozzle to work doesent it??? It seems like the boat just doesnt want to plane off.
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Thursday 4/18/02 put a little silicone rtv gasket maker on ride plate gasket seemed to do better for about 3 minutes in water then went back to her old self... Could the ride plate gasket be giving me all of this grief??? The gasket looks fine any suggestions anyone???
 

ODDD1

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Yes rich, ride plate gasket/ ride plate itself will cause this...have seen many ride plates 'sneezed' off the bottom of the pump by people starting them up out of water...recheck all fasteners on the plate, caulk the gasket to eliminate any leaks between plate an hull, it has to be a PERFECT water tight seal....
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Ok got new ride plate gasket today $57.00 not to bad but in stock got it on the boat put boat in water boat is better but not the best she will do 20 at best it just doesnt seem right for a mercury 90 with a 14' boat, could I be wrong??? If someone has their opinion on this boat I would greatly appreciate it. And thank you guys for all of the input so far it has helped alot
 

Ledif7

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Re: MERCURY SPORT JET 90 HP TOO SLOW

I have a regal rush 1994 , same mercury 90 hp . I just got it. I tested it in the bay and seems to go too slow. mileage metter broken. I will try the same thing put a gasket to see if it goes faster. When I hit the trottle it makes a noise like the impeller runs out of water. I will keep you posted on the results.
 

ODDD1

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Rich...last jazz I fixed ride plate on an 'Adjusted' the trim......42 mph....with a 90 SJ...you got a ways to go....
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

42 MPH would be like hitting to lottery to me at this time. You raised a good question how do I adjust the trim on my jazz does the gate have to be totally up and out of the way of the nozzle or is there some tricks I dont know about???
 

ODDD1

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Rich, the gate doesnt hang down in the nozzle...make sure it clears....trim is accomplished with the rear two ride plate anchor bolts....they had spacers on them, didn't they? Add additional washers to push the back of the ride plate down....will help boat run flatter, especially with a light load...
 

Ledif7

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Re: MERCURY SPORT JET 90 HP TOO SLOW

I have a 94 reagal rush a 90 hp. The rudder has a opening at the bottom end . About 2 inches wide and 2 inches deep. Is that the way it is suposed to be? At the bottom it has a screw with something round atached to it but it seems it has no used for it. I was wondering it something was missing, thankyou.
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

ODDD1, I am scared that if I space the ride plate rear I will lose a good seal with the ride plate gasket or am I misunderstanding you??? you are talking about the 2 screws closest to the nozzle that bolt in to the stator correct?
 

RICHRICH26

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Re: MERCURY SPORT JET 90 HP TOO SLOW

Led, the nozzle is suppose to have a notch in it to direct some of the water down. The round thing you are talking about is your zinc. If it is badly pitted I would replace it before you start getting galvanic corrosion on your engine parts
 
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