Hello everyone, I have an 09 Speedster 150 with a 215hp motor that has 78hrs on it. It was dealer serviced at 72hrs with an oil change, new plugs & general pre-season checkup. The motor runs smooth at idle (about 1,800rpm) and any speed above 2,500rpm with no hesitation going to WOT. However, it does have a surging problem when I move the throttle just off of idle (the motor will constantly surge between 1,800rpm and 2,400rpm). If I keep increasing the throttle the surging will stop at 2,500rpm and run smooth again. Has anyone had this problem or know what is causing it? Thanks for your help.
Motor Surging
- Thread starter rcnut
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Based on the reply’s, it seems this is somewhat common and nothing that could become serious over time which was my concern. At this point I’m not going to worry about it but I will post any updates if anything develops. I would like to thank everyone for taking the time to respond and share your experiences, I appreciate it very much.
Jcamaro
Member
This is caused by minor cavitation. It is not an actual issue. What is happening is that your impeller is moving fast enough that it's drawing out the available supply of water since the boat is moving slowly and there isn't enough pressure on the bottom of the boat the keep the jet pump fed with the amount of water you're expelling out the nozzel. Water is fed into the tunnel in the transom by the pressure caused by forward motion at speed.
Every jet boat will probably do it at a certain RPM depending on many different factors even down to water temperature, fresh/salt water etc.
For the longevity of your wear ring and impeller...avoid that rpm.
That’s interesting and something I never considered! I’ll hookup a garden hose and try running it on the trailer. If this is a cavitation issue it should run smooth, right?
Jcamaro
Member
Yes and since the RPM's are pretty low you should be safe. Should hold exactly where it's supposed to. Just don't run it for more than a few minutes as per the normal flush procedure.
Please let us know your results. I'd like to know if I'm crazy or not.
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pete63
Active Member
good theory...
i wouldn't say cavitation but low pressure at the intake. but i'll give a 9/10 for this one.
Mike Barton
Member
My 2009 challenger does the same thing just north of its 1800 idle. If I coast into the marina @ 2500rpm it'll swing up or down 50-200rpm but goes away once it gets into the 3200 range. No issues at 6000+ rpm so could just be normal for these boats. Just had the boat out this weekend and romped it for a minute or two at 7800rpm going 46mph
Jcamaro
Member
Easier way to check would be to run it out of water at the RPMs. I'm taking mine out tomorrow so when I flush the sytem I will check that RPM to see if it still does that surge. I'm still thinking it's impeller speed/water related.
This is not the definitive test. Your throttle position will be different at identical rpm with load vs no load. Surging is typical of a lean condition although I don't totally discount the cavitation theory.
pete63
Active Member
i'm not discounting the theory, but there is a few posts & threads about idle speed variations. water load at the lower speeds may be causing the ecm to hunt up and down to maintain the lower rpm. eg. different fueling maps for load and rpm?
Okay, I had a chance to test it on the trailer this weekend. The surging was still there but it acted different like it was surging at a faster cycle. I called my Seadoo dealer and explained symptoms to him. He thought I might have a dirty idle bypass control valve and suggested that I try adding "Sea Foam" to the gas tank to see if that would clean it. I normally don't believe in additives but considering a can of Sea Foam cost $7 vs just north of $200 to replace the valve it seemed worth a try. I'll have the boat out all next week (vacation) and will let you all know what happens.
Jcamaro
Member
Good feedback.
I use seafoam as fuel stabalizer in all of my vehicles during winter storage. That way the first tank through cleans it out. The Corvette guys swear by it. Let us know if it solves your issue. My sportster got seafoam as least once a year so I'm not sure that it will solve your surge issue or not.
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I ran 2 full tanks of gas with Seafoam last week, no changes with the surging issue. Like ZRXGuy says, it's annoying but fortunately it only happens just off of idle. Have a great summer everyone!
My GTX 4-tec just started doing this. I have 3 highly skilled water skiing daughters. The surging makes it very difficult for them when they ski with their foot in the rope. No problem pulling two of them up, accelerates smoothly. We usually run at 25 mph when skiing. That's when the surging occurs. Going to try changing spark plugs.
xintersecty
New Member
My own boat does this at 6200 rpm which seems to be ideal rpm for cruise. GARRR! I cleaned my ICV when I was putting in the new motor. Yeah the 200 bucks for it is not worth it.
Jcamaro
Member
6200 rpms is ideal for cruise. I get great mileage at that speed.
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