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Inconsistent RPM's


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While I've been running my 'Bu running every other weekend or so on the "Fake a Lake" to keep it running (I did not winterize since in GA), I've noticed a problem with the RPM's fluctuating when I get to about 1,200 RPM.

It is very consistent, and the boat runs very smooth at 600, 800, 950, 1,100 RPM, and then right when I move the throttle to get it up to 1,200 it starts to rev up and down from 800 RPM to 1,700 RPM and continues to do so until I move the throttle up or down out of that RPM range.... After I go past that 1,200 to 1,300 RPM range, it runs just fine again, and all the way up to 2,700 RPM it is silky smooth. When I come back down it again starts to rev when I try to stop the throttle at about the 1,200 RPM area.

Do you think this is a bad fuel filter, or do you think it is in my throttle cable or something more serious?

Any help would be appreciated.

Thx, Mook

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While I've been running my 'Bu running every other weekend or so on the "Fake a Lake" to keep it running (I did not winterize since in GA), I've noticed a problem with the RPM's fluctuating when I get to about 1,200 RPM.

It is very consistent, and the boat runs very smooth at 600, 800, 950, 1,100 RPM, and then right when I move the throttle to get it up to 1,200 it starts to rev up and down from 800 RPM to 1,700 RPM and continues to do so until I move the throttle up or down out of that RPM range.... After I go past that 1,200 to 1,300 RPM range, it runs just fine again, and all the way up to 2,700 RPM it is silky smooth. When I come back down it again starts to rev when I try to stop the throttle at about the 1,200 RPM area.

Do you think this is a bad fuel filter, or do you think it is in my throttle cable or something more serious?

Any help would be appreciated.

Thx, Mook

Could it be the fact that by the time you get that baby roaring at 1200 it sounds just so darned excellent that you get a case of motorcycle throttle and just start jazzing it? Gotta be it.

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Kind of sounds similar to a fuel starvation problem. Fuel filters are cheap, that would be a good place to start. Make sure you replace all of them. There are two in my boat. One by the motor and one off the gas tank.

Adding some iso-heat to the gas is a good idea too to ensure it absorbs any water that may be in the gas from condensation. If you didn't add stabil at the end of the season, you might have marginal fuel.

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It wasn't the "jazzing" this time... (although when summer time comes around, I am a habitual "jazzer".)

I'll start with the fuel filters and see what that does. I did add Stabil to the gas and filled the tank to minimize condensation before winter hit.

The revving is something that I had noticed a little bit this past summer, but not to the extent that it was fluctuating yesterday. Hoping it is not a big deal, but...

Any other ideas on what may be causing it would be appreciated.

Thanks, Mook

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After thinking about the filter being the problem, it doesn't make as much sense when you consider that it only revs up and down at a certain RPM. If it were the filter, I would think it would rev or cut off at various levels or all levels....

Let's say that it is the throttle position sensor, how is this problem fixed?

Do I need a whole new throttle, or can an individual sensor be replaced?

Also, is it a DIY job that I could do myself (I'm pretty handy), or something I need to take it into the dealer to address?

Thanks again for the help!!! Clap.gif

Mook

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When my filter was bad, it ran great on the fake-a-lake. However, when you put it in gear in the water, it was a whole different story.

The throttle sensor sounds more plausible, but for about 10 bucks, it doesn't hurt to change the fuel filters too.

Best of luck.

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Yep. I'll definitely be changing the filters this spring, but any insight on the throttle sensor would be great.

I may need to start another post with that as the topic.

Thanks Again!

Mook

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The throttle position sensor can be in almost all cases replaced by its self. Some throttle position sensors are adjustable some are not. If it is not adjustable it should be pretty easy to change if it is adjustable you will need the specifications for the voltage at closed throttle to properly set it up when installed.

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I thought of another possibility, if my perfect pass is turned on it will cause a slight lag in light acceleration so it could possibly cause that much fluctuation with no load on the engine.

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I thought of another possibility, if my perfect pass is turned on it will cause a slight lag in light acceleration so it could possibly cause that much fluctuation with no load on the engine.

That's a good call. Our last boat had that dead spot with PP engaged & from what I've read it's there in every PP system (even PP support will tell you that). It will fluctuate & surge at that spot until you give it enough throttle to get past it. IIRC on our boat it was at about 1900 rpms (maybe a bit less, can't remember for sure).

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I believe that PP was off when I was running the engine, but will check next time I run.

If this is something we live through as "Bu owners, I don't think it is a problem for me as far as performance while boarding or skiing. (we'll see this summer)

I just wanted to make sure it wasn't something more serious that could get worse and cause serious damage....

Mook

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If it's like the motor is "surging", then I second the PP issue. A while back, I took my boat in for some work. The mechanic called me stating that it had an idle problem. After scratching our heads for a while, I told the mechanic to make sure PP was off. That did the trick. I bet you dimes to donuts its your PP given your description. Sounds like you're hitting that "dead spot" as described above by Wakegirl.

Edited by SGY
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After scratching our heads for a while, I told the mechanic to make sure PP was off. That did the trick.

That sounds about right for a NauTank mechanic. You had to tell him (or her) what the problem was. ROFL.gif

in jest, as I'm sure you know, SGY

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You guys are good.... Thumbup.gif

Sure enough, before I cranked it up this past weekend, I checked PP to see if it was on or off, and it was "ON"!!

So, I turned it off and no dead-spot, revving, or inconsistent engine. Just smooth as silk....

Thanks again for the brain power. Once again, you've saved me a trip to the dreaded dealer!

Cheers.gif

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After scratching our heads for a while, I told the mechanic to make sure PP was off. That did the trick.

That sounds about right for a NauTank mechanic. You had to tell him (or her) what the problem was. ROFL.gif

in jest, as I'm sure you know, SGY

I took it to the Malibu dealer here in Colorado. We don't have a CC dealer.

Just kidding--about the Bu dealer. I took it to a old meph addict that claims to be a boat mechanic. I am now having Skisix do all the work on my boat.

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