1999 Seadoo Challenger 1800 Sportboat surging

[old44272]

Hello all,

I've got a 1999 Seadoo Challenger 1800 sportboat with the 787 Rotax 110HP engines. The starboard engine surges at a higher RPM. The boat comes out of the hole fine and will maintain 3500-4000 RPMs no problem. However, any further push of the throttle and the engine will surge....it will go up in RPM and then come back down to 3500 or so and then surge back up and then down. I replaced the firewall fuel filters and hit the carbs with cleaner, however I have not had the carbs off of the engines or taken them apart. Does this sound carb related, or could there be something else going on like fuel pump, etc.? I'm not very knowledgable of these motors, but in reviewing prior threads here and other places I'm learning. The boat is bone stock and has not been apart other than having the exhaust manifolds off to have the round plugs rewelded on (they corroded). The port engine seems ok, so I don't think it's bad fuel. Thanks for the replies!

[Technical Support]

Re: 1999 Seadoo Challenger 1800 Sportboat surging

rebuild the carbs first, see if that solves the issue. Carbs should be rebuilt every few years.

[old44272]

Re: 1999 Seadoo Challenger 1800 Sportboat surging

Hey SBT, Thanks for the reply. I have read your online article about rebuilding the carbs and it looks like something I can handle. But I had a couple of questions:

1) Should I replace the needle and seat? If so, how do I know what size to order?

2.) I have read about pop off pressure....I would need to order the pop off pump as well. But how do you use it? Specifically, what the heck do I do with the thing?

Thanks from a newbie backyard ski mechanic!

[Technical Support]

Re: 1999 Seadoo Challenger 1800 Sportboat surging

Use a magnifying glass to see what the needle size and jet sizes are if you are replacing them. The pop-off gauge is installed into the fuel inlet of the carb, the diaphragm is removed and all other hose ports are blocked off. You will spray wd-40 around the needle area to keep things wet, then pump up the pressure pump to see if the needle pops at the recommended psi for your model. Try to down load from seadoomanuals.net a factory manual for your boat or from a ski that yr that uses the same engine it will help you out with all the repair issues you may encounter.

[old44272]

Re: 1999 Seadoo Challenger 1800 Sportboat surging

Great! Thanks! I ordered the rebuild kits from you guys. I guess my question about the needle and seat is whether or not it is recommended to replace these during a rebuild? Thanks again.