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Old Today, 12:18 AM
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JMLVMI JMLVMI is offline
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Lightbulb High RPMs for the speed...help me debug!

Just picked up a new-to-me 2007 X2, MCX, 1.5:1 ZF Hurth V-drive trans w/ 650 hours on the clock. Doesn't appear to be abused in any way, so no reason to think the engine/trans was either. Had a marine survey (on the trailer) done and nothing came up there.

Take it out, boat accelerates and everything fine as far as I can tell, don't get "the feeling" that anything is wrong, no alarms, etc. Find out that at 27ish MPH I am turning almost 3600 RPMs.

Swapped out the prop (OJ 522 14.75 x 15.75, no apparent damage) for the stock prop (13.7 x 17) and had the same issue tonight.

Checked the transmission dipstick as soon as I came out of the water tonight before it could cool off...fluid doesn't smell bad, is not discolored (shows as a light brown, no dirt or particles), and is right between or at the 2nd marker on the dipstick (see attachment).

The RPMs do vary trying to keep the boat at speed, but I chalk that up to PerfectPass.

Shaft and everything seems to be in alignment, but the boat does turn hard left (increases as speed increases) moreso than my 195.

I'm at a loss...I purchased a Mityvac Fluid Extractor which gets here Thursday, so I plan to suck out the transmission oil (15W40) and see how much is really in there.

Any other ideas guys?!!? I feel like it should be close to a 100:1 RPM to MPH ratio on plane.
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Old Today, 04:26 AM
FrankSchwab FrankSchwab is offline
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You've covered about everything I could think of.

I guess one question is, do you trust the tach? Or the Speedo? Maybe one of them is lying to you.
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Old Today, 06:53 AM
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Got a slalom course around or GPS app on the phone? Slalom timing, yeah you could get the xx.xx time but basically, 30 mph 19 seconds gate to gate, 32 mph 18 seconds, and 34 mph 17 seconds(i.e. 16.95)
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Old Today, 07:07 AM
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Yes, check with GPS. First prop numbers sounded about right. The stock prop should be real close to 1:1 ratio. I don't think you have any transmission issues, you'd notice slipping and shuttering if so. If you have paddle wheel pp, that may be the issue.
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Old Today, 09:28 AM
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JMLVMI JMLVMI is offline
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High RPMs for the speed...help me debug!

Thanks guys...no slalom course nearby. Speedo, tach and PP (paddle wheel) report the same speed and RPMs. Do they both pull data from the same paddle wheel and sensor, respectively?
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Old Today, 09:48 AM
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If you're sure speed is right - I'd have it checked. download a free gps speedo app. 3600rpms seems a tad high for 27mph. could also be a problem with the tach. You can also have get a automotive multimeter with tach to confirm rpms.

either way you are uncomfortable with the data you are getting from tach -

regarding the left turn pull - your turning a big screw
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Old Today, 11:44 AM
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Quote:
Originally Posted by mikeg205 View Post
If you're sure speed is right - I'd have it checked. download a free gps speedo app. 3600rpms seems a tad high for 27mph. could also be a problem with the tach. You can also have get a automotive multimeter with tach to confirm rpms.

either way you are uncomfortable with the data you are getting from tach -

regarding the left turn pull - your turning a big screw
Appreciate the feedback Mike, yea the pulling doesn't concern me...cavitation, no tracking fins, etc...certainly not on rails like the Prostar but still fun

I'm going based on sound as well. It seems to sound like it's revving high, but that could just be confirmation bias...

I'll bring out the GPS app tonight and see if I can borrow a multimeter. Just don't want to do any lasting damage if I'm running the boat when I shouldn't be
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