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RSRBOB, Technician
Category: Boat
Satisfied Customers: 1077
Experience:  Former Yamaha Factory Service Rep, Dlr Line Tech, Serv Mgr, G/M
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I have a 94 750sl Polaris jetski, it has a new top end from

Customer Question

I have a 94 750sl Polaris jetski, it has a new top end from sbt. I notice more than normal amount of fuel accumulating in the spark arrester housing. Fuel was squirting up and out of the center carb. Pulled the carbs and intake manifold to look at the reeds and found the center Reed was missing/broken off. I replaced all the reeds and rebuilt the carbs. Put it all back together and started ski. It will not idle and over revs out of control. I reset the low speed screw .5 turn out as per manual on all three carbs. It sound to me like the engine is leaned out, I'm not sure where the air could be coming from. The injection ports are blocked and I mix the gas. I'm out of ideas and half afraid to start it and over rev it and blow it up.
Submitted: 2 months ago.
Category: Boat
Customer: replied 2 months ago.
I have rebuilt mikuni diaphragm carbs before so I'm confident I rebuilt them correctly. I did not do a pop off test on each carb, I pulled the carbs again and will do the test. The throttle cable was connected properly and the butterfly on each carb was closed when the engine over reved.
Expert:  RSRBOB replied 2 months ago.

Hi and thank you for your question.

Two things come to mind. First, have you tried backing off the idle speed adjuster screw? I would suggest setting it manually by removing the flame arrestor and looking down the throats of the carbs. Back it off until there is just the smallest of gaps between the throttle plate and the carb body. We are talking wire size drill bit clearance here. Since it is tending to rev uncontrollably, you are safer to miss it on the low side, and have to use the throttle trigger to keep it running, than having it run wide open with no way to control it. The other thing I want you to check before you try to start it is to make sure you have slack in the throttle cable. If there is no slack in that cable, it can be holding the throttle plates open as well. You can also adjust the throttle cable without the engine running by putting slack in the cable, a lot of slack, then, hold the trigger wide open. It should stop at the grip, Now, grab the pulley on the carb bank and see if the throttle plates are wide open or not. Correct throttle cable adjustment is when the throttle plates hit the wide open stop just as the trigger hits the grip. Water craft throttle cables typically run a lot more free play than motorcycles. As long as it gets the throttle plates wide open, it is not going to affect performance. So you may find your throttle trigger moves quite a bit before it starts picking up the throttle. Just remember that is normal. All you care about is you can get WFO with the trigger on the grip.


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