My 99 Speedster has one motor that has been starting to surge. As you run across the lake at speed the rpm will drop and maybe hold for a little then it comes back up. A first it would do this and run like that for a little while then clear up and run fine the rest of the day but now it keeps doing it. On a recent trip out that motor quit and would not restart so i took it home and the next morning it would start but when you tried to give it gas it would die. I pulled the fuel line and it did not have a very good flow so i put a new mikuni high flow fuel pump on (same set up as the other motor) and replaced the lines to the carb and the vacuum line and a new filter. Yesterday i took the boat out and i am still getting the surging. When i run it full throttle it may run up to 7000 rpm and as you go it will drop down in rpm to maybe 3-4000 then run a little and come back up to 7000 rpm. I did notice that if i back off to around 5000 rpm i did not get the surging as bad, this makes me think its a fuel issue but at this point im not sure and dont know what to do next. If anybody has any idea of what it may be please let me know. Thanks
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99 Speedsteer engine surging
- Thread starter yamaha188
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Waterluvr
New Member
Most likely, and a carb in perfect working order tuned to it's intended application with the correct airbox is only as good as the condition of the rotary valve and cover clearances that govern the manifold pressure and air velocity that allows it to operate and deliver fuel and air as needed.
There are so many ski's and boat's still in use at the age of 15-20 years now that have never had the rotary valve serviced that it should at least be inspected and clearances measured while the carbs are off for service.
Sorry forgot to mention the carbs were rebuilt about this time last year by Nick at Westside. I'm not sure about the rotary valve, i have owned the boat less than 2 years. What can i do if the tolerances are off on the rotary valve, order a new cover or can they machine it down to work?
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