Sportjet 90HP once again..HELP

[Thena]

One problem after the other.. I wonder if it is really worth it!! After changing half the engine..pistons-carbs-stator e.t.c. I had the boat running for about a month with no problems and suddenly one day I was running low on fuel but going about 25mph when the engine increased in rpm but the boat stopped moving!!!<br /><br />The boat now goes up to 5mph no problem and the engine sounds fine but when I increase the throttle rpm goes up and boat slows down as if the axle is turning without the prop turning. <br /><br />I checked to see something went inside the jet drive but I couldnt see anything..<br /><br />My boat is a donzi 152 medallion. Any suggestions?

 

[SB]

Re: Sportjet 90HP once again..HELP

It sounds very similar to what happened to my Sport Jet 90 when a "mechanic" blew out the ride plate by backfiring the engine. There are two types of flush attachments for that engine. One is designed to allow the engine to be run and the other is just to flush without running the engine. Guess which one he used. <br /><br />Anyway, maybe your engine backfired when you were running out of fuel and damaged the ride plate or gasket. I couldn't straighten mine and it cost around $200 to replace. That was the last time I let anyone else work on the engine.<br /><br />Good luck,<br /><br />Scott

 

[wakataka]

Re: Sportjet 90HP once again..HELP

Lucas - <br />I've recently purchased a Bayliner Jazz with the Sport Jet 90 that had the ride plate blown out by a backfire in the trailer. When the plate was leaking exhaust, my boat acted like you describe. <br /><br />The leakage comes not from the rubber gasket around the outside of the plate, but from between the ungasketed metal to metal seal where the ride plate meets the impeller screen. There are 6 or 8 phillips head screws that hold the ride plate up to the jet drive unit. It can be leaking enough to cause problems and still look like it is tight up against the bottom of the boat. On mine, I was able to seal the leaks (at least temporarily) using blue silicone. I used a hydraulic jack to push the ride plate up against the boat while tightening the screws. Be sure and use LocTite thread locking compound on the screws so they don't vibrate loose. It doesn't take much exhaust leakage to cause cavitation in the impeller.<br /><br />Hope this helps.

 

[Thena]

Re: Sportjet 90HP once again..HELP

Thats exactly what happened. I had a chance to look at it this weekend and discovered that for some strange reason I was missing half the screws on the plate over the impeller. The other half were extremely loose. How could this have happened??? <br /><br />I will push the whole plate back in because the larger plate behind it also came out a bit. From what I understand the rubber around the larger plate is not the problem but the space around the smaller plate. Where should I put the silicone? Around the smaller plate?<br /><br />How could the screws be so loose? from vibrations? Is there more damage to it or do I just push it back up?? Did I damage anything from the inside? i.e. gasket e.t.c.??<br /><br />I am on vacation now. Should I push my luck and continue using it (Maybe making matters worst) or should I stop and wait till I get back???<br /><br />Furthermore just a question to everybody.. Are jet drives and jet engines this sensitive or am I the only one who visits the mechanic once every week!!!!!!!!!!!<br /><br />Thanks<br />Lucas

 

[kenimpzoom]

Re: Sportjet 90HP once again..HELP

Search the forum on the Sport Jet.<br /><br />These engines are junk, specifically the electronics.<br /><br />Mine just went out yesterday, and my buddies went out last summer and now we are trying to fix both.<br /><br />Ken

 

[wakataka]

Re: Sportjet 90HP once again..HELP

Lucas - <br />If your plate is not bent, you can probably just put in new screws and be done with it. The manual says these screws are self locking and should not be re-used once they are taken out. In a pinch, I would just put them back in with LocTite. <br /><br />If you want to see a drawing of the jet assembly, go to<br /><br /> http://www.stemtostern.com/partsimages/SPORTJET/820612/47.gif <br /><br />I put silicone around the big rectangular hole in the inner portion of the ride plate, which is part number 54 in this drawing.<br /><br />This plate can be damaged if the boat backfires while being run out of the water. The ride plate covers a large cavity that is effectively the muffler on these boats. This cavity is full of water when the boat is afloat. If you run it on the trailer, the unburned gas that is pumped from the engine while cranking accumulates in this cavity, then when the engine finally starts, KABOOM!. The ride plate can be blown off the bottom of the boat. I bought my boat after this happened to the previous owner. It was very obvious that the plate was bent. It was hanging down about 1.5 inches in the front. My efforts at straightening it were not successful, hence the silicone fix. This is only temporary. I have ordered a new ride plate.<br /><br />Good luck!

 

[wakataka]

Re: Sportjet 90HP once again..HELP

Lucas - <br /><br />Regarding damage from the loose screws, there is really nothing other than the screw holes themselves that should be damaged. There is no gasket around this inner lip of the ride plate. <br /><br />Running the boat with cavitation (engine revving with boat not moving) is not a good idea. The cavitation can damage the impeller and I suppose that it might also put a lot of air bubbles into the engine cooling system. If you can run it at low speeds without cavitating, it shouldn't hurt anything. That's my free advice, which may be worth what it cost you!<br /><br />Martin B.