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TOPIC: 1998 Seedoo GS Jetski 717cc Rotax engine

1998 Seedoo GS Jetski 717cc Rotax engine 17 Apr 2012 23:03 #1

  • phil
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Ive cut a groove in my jetski. Its waiting for some other minor repairs and a new battery. But as soon as i get that done ill get it out on the water and let you know how it goes. Theres no speedo or any instrumentation on the thing so ill just have to see how it feels to ride and see if it costs me less to run.
The shot of the engine below is the twin carb model, mine was a single carb.
These engines have a rotary valve in the crankcase that alternates the fuel delivery to each cylinder.
Anyone got any ideas/predictions about combining how this will affect the groove?

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Last edit: by phil.

Re: 1998 Seedoo GS Jetski 717cc Rotax engine 25 Jul 2012 14:12 #2

  • phil
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Finally got some decent weather to test the groovy jetski. Nice and smooth acceleration , and the little 717 c engine keeps up with a 2011 Yamaha waverunner 1000cc 4 stroke. Ill try and keep you updated so long as the good weather holds out. Anyone got any tips for jetting the carb for better economy , jetskis are thirsty beasts.

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Re: 1998 Seedoo GS Jetski 717cc Rotax engine 25 Jul 2012 14:25 #3

  • Gadgetman
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That, my friend, is GOOD NEWS! Keeping up with another with a 33% larger engine?!?!

As to rejetting, I think I would try using a restrictor plate. Where the carb mounts to the intake, simply cut a sheet of aluminum flashing that will reduce the size of the port by 25%.

I would try that first. This will have the additional effect of further increasing the vacuum available at the valve.

Have FUN on that SkeeDoo, amigo!

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Re: 1998 Seedoo GS Jetski 717cc Rotax engine 30 Jul 2012 11:50 #4

  • phil
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So the restrictor plate goes between the carb and the engine after the groove and not between the air filter and carb before the groove?

And by 25% smaller do you mean 25% smaller diameter or 25% smaller cross-sectional area?

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Re: 1998 Seedoo GS Jetski 717cc Rotax engine 30 Jul 2012 16:20 #5

  • Gadgetman
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Yes to the positioning, Phil.
And 25% diameter should do nicely.

I'm getting a report in today on some prototype testing for an insert for small engines that should be fairly interesting. This report will give me more data to work with and will be shared freely with the group.

Isn't this stuff EXCITING?

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Re: 1998 Seedoo GS Jetski 717cc Rotax engine 07 Aug 2012 15:27 #6

  • phil
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Ok, so we took this to the beach again at the weekend. Havnt done the restrictor plate yet. But some friends of mine capsized it and i had to get the plugs out to get the seawater out of the engine. Last year the plugs ran a nice tan/brown colour (as they should be). This year after grooving seems like the engines running slightly richer (black sooty plugs) could be the auto-lube pump needs adjusting, need to get a new cable for that.

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