1998 Seadoo Sportster Single Engine

[jim7]

Hi I am doing a complete rebuild of a 1998 Sportster I was told the engine was replaced by SEADOO in 2002.... Long story why..... I just now realized from the manual... these come stock with a 720 SINGLE CARB engine.....This one has a 720 dual carb set up.... The engine serial number is 4677207 Is there any way of telling what year this engine is??? I also pulled the carbs apart and they have1.2 needle and seats. Anybody have any ideas what year this engine is ...or when they went to a 2 carb set up at seadoo>? should I replace the seats with 1.2 or go to the 1.5 that is in the manual??? keep everything the same or go with what the book says???On more thing what pop off pressure do I use for a 2 carb set up???? like this......HELP

 

[CaptSteve]

From what I have read, the 1999 Speedster SK and Sportster 1800 used 717 engines with 2 Mikuni BN-40-38-51 carbs per engine. If this the carb you have, then the pop-off is 36-40. The main jet is 167.5 and pilot jet is 70

 

[jim7]

Ok Quick update ....... I have totally disassembled the carbs and here's the info..... Needle and Seat 1.2 Main Jet 130 Pilot Jet 67.5 BOTH carbs are built this way and both were set 1 1/4 out low speed and 1/8 out high speed screw..... I cannot find any machine that had these jets and setings????????????Where the did this engine come from>>>

 

[Dr Honda]

That's the stock jetting for a 96 Sportster. (pop-off should be around 38-50 psi)

You can leave it there if you like... it should run fine. If you start playing with the N/S size... you will have to jet it closer to one of the jetski models.

As an FYI... the low needle should be at 1-1/4 turns out, and the high should be at 0. (but 1/8 turn out will give it just a little more fuel up top)

 

[jim7]

Thanks guys I guess it's a 1998 boat that Seadoo replaced the engine with one they had sitting around and it turned out to be a 1996 720..... Now two quick questions did the 1996 sportster have dual carbs??? Also how can I tell if they replaced the coil/plug wire box??? Just in case I have a coil or part in that box go bad should I be looking at 1998 parts or 1996 parts like the engine??would rge mpem firm those two years be the same two???

Thanks

 

[CaptSteve]

They also used that jetting on the 1997 Explorer with the 717 engine. The carbs on the 1997 were MIKUNI BN38i-37-17 on the MAG and BN38i-37-18 on the PTO. These had a pop-off of 36-40. The 1997 Explorer was a single engine dual carb setup.

 

[Dr Honda]

Thanks guys I guess it's a 1998 boat that Seadoo replaced the engine with one they had sitting around and it turned out to be a 1996 720..... Now two quick questions did the 1996 sportster have dual carbs??? Also how can I tell if they replaced the coil/plug wire box??? Just in case I have a coil or part in that box go bad should I be looking at 1998 parts or 1996 parts like the engine??would rge mpem firm those two years be the same two???

Thanks

The 720 engines, and their electrical systems are the same. The 720 is a simple ignition, with a HV CDI system. The Ignition coil has the CDI built into it. You can use a coil from ANY 720 engine, and make it run. The rest of your electronics are probably going to be for a 98. I'm not sure if they changed the MPEM, but I'm going to assume they were not changed. You can verify that with any of the online parts stores. Regardless... they are discontinued from SeaDoo... so if you have an MPEM go bad... you will have to find a used one, or just replace it with a jetski version. (not a big deal) AND... if you don't short it out... or try to jump start the boat... you will probably never have a problem with the MPEM.

 

[jim7]

Thanks for all the help... I got myself the 96 manual for the engine and the 98 for the rest of the boat.... Waiting on a couple of more parts and the assembly process will begin.... Thanks again....Just cleaned the engine bay today... letting it dry.... thru hall mod next weekend and then put everything else back together....