Synhronizing engines on a 1999 Speedster SK

[joe ferralli]

Hi Everyone,
I have a 1999 Speedster SK with 2 717 engines. I rebuilt the carb on the starboard side and Im having trouble getting them both to accelerate the same. The starboard side now hesitates a bit behind the port engine and then over revs. I just checked the pop-off pressure and it's at 48psi (the manual says it should be 38psi +/- 12. Do I need to have it set at the same exact psi as the port carb or does it sound like a needle setting? Any guidance would be greatly appreciated.
Thanks
Joe

 

[fastboatman29212]

I think a lower pop-off would be better, maybe under 40, but it comes into play during the 1st third of the throttle position. I would 1st recommend reading the "How To" tech article about carb adjustments and tuning. High rpm's may be a symptom of cavitation and a worn wear ring around the impeller. That needs to be ruled out too.

Here's a link to some good reading. I was able to completely solve similar problems with my 97 Speedster by cleaning and adjusting the carbs. I hope this helps.

http://www.seadooforum.com/showthread.php?4151-Snipes-Korner...

 

[joe ferralli]

Thanks

I appreciate the link and am reading it now. The carb was running perfectly before the rebuild so I'm assuming it's a setting somewhere that's causing the issue. The carbs we're never rebuilt so I thought I'd give them a good cleaning and rebuild...should have left it alone. The wear ring is right in spec (I just checked them while I was changing the impeller oil on both pumps). I read the service manual a couple of times about pop-off and still don't understand what it effects.
Thanks again,
Joe

 

[fastboatman29212]

Here's another link that might help. There is some repetition. It's basically right out of the FSM. My pop-off is right at 40psi for Mikuni square body carbs.

http://www.seadoosource.com/mikunitests.html

Also, make sure your throttle cables are adjusted properly. Here is what Dr. Honda said about different rpms between the 2 engines in another post and then he describes how to properly adjust throttle cables. He's helped me a lot.

1) Engines wear differently, and make different power at a given throttle position.
2) impellers/pumps get damaged by stuff in the water, and will load the engines differently.
3) the pumps/seals can leak, and will cause very light cavitation, and will load the engines differently.

With that said... there was a reason that boat manufacturer gave you a throttle for each engine. It's because if you spend the time to perfectly sync the engines at 75% power... next week... it won't be the same.

The proper sync'ing method is....

1) Remove the air boxes so you can see the carb butterflies.
2) Open the throttle levers to full.
3) Adjust the cables so the carbs are fully open, but not quite touching the carb stop. (if they do, you can break a throttle cable)
4) close the throttles, and put the airboxes back on.
5) put it in the water, and adjust the idle so they are the same (don't try to adjust them out of the water, because it can dramatically change with a load on the engine)