Interesting question about over revving.

Jgcrock99

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So I have a 96 Chaparral 1930ss with a 4.3lx merc. I have had this boat for 3 years and been out more than 10x a year. I have tested WOT more times than I can count and have a really good feel for the rpms on the boat. I have a 3 blade 21"p propeller and have always turned 4800 rpms at the absolute max unless I put on my 17" 4 blade. I replaced the hub of my 3 blade propeller mentioned above and because I noticed a small crack when I was swapping props a few weeks ago. Last time I went out on the lake I was driving as always and went for WOT. Luckily I looked down soon after planing because I was exceeding 5k rpm and still had throttle left. I am not crazy and I have done nothing else to the boat other than change the hub of the propeller. I was actually considering a full tuneup because the boat has not been running optimally this season. Has anyone else ever seen or heard of anything like this. I would suspect a faulty tach but my top speed was faster too. I'm fine with having extra tbrottle I just have to watch my rpms much more closely now.
 

Scott Danforth

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Verify your tach is still reading correctly

What pitch is your new prop?
 

Jgcrock99

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Verify your tach is still reading correctly

What pitch is your new prop?

I don't have a new propeller I only changed the plastic hub. The 17" I mentioned is a new prop and it definitely will overrev but the 21" is the same ole dinged up propeller that came with the boat. I did a great deal of rpm testing earlier this season as I was propeller shopping. I considered getting the tach tested and I may still but the speedometer still registers the same it did at the corresponding rpm. At 4800 it registers 43 on the speedo and still does I have throttle left now and exceeded 45 before I pulled back for fear of damage.
 

Sea18Horse

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Did you ever get a chance to verify that your throttle linkage was actually giving you full throttle prior to you prop hub work? Have you done anything else, maybe seemingly unrelated that could have had an effect along these lines? Just spitballing here as this seems the only likely scenario. Occams razor and all that.

Cheers.....................Todd
 

Jgcrock99

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Did you ever get a chance to verify that your throttle linkage was actually giving you full throttle prior to you prop hub work? Have you done anything else, maybe seemingly unrelated that could have had an effect along these lines? Just spitballing here as this seems the only likely scenario. Occams razor and all that.

Cheers.....................Todd

Truly nothing I haven't done before. Running rough so ran sea foam but I do that every season and about every third or fourth tank. I guess I've never verified my throttle linkage fully engaging so maybe it finally broke loose but my controller is always at full forward. Could the hub have just been worn out and somehow causing resistance or a vibration that was making the engine work harder. I thought it was strange.
 

alldodge

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the 21" is the same ole dinged up propeller that came with the boat.

A dinged up prop will cause cavitation and increase slip. Get the prop fixed for better economy and speed.

You have a TBV and the rev limiter is set for 4850 rpm, so I would get your tach checked
 

H20Rat

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You have a TBV and the rev limiter is set for 4850 rpm, so I would get your tach checked


They have a rev limiter? Hmm... Makes me question some of my prop changes this year, as my new boat was hitting 5200 rpm and I had no reason to suspect the tach, but...
 

Jgcrock99

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A dinged up prop will cause cavitation and increase slip. Get the prop fixed for better economy and speed.

You have a TBV and the rev limiter is set for 4850 rpm, so I would get your tach checked

Does the Rev limiter only engage when the drive is running? Even when I didn't suspect a problem I could Rev over 5k when running in neutral. It's either always been broken or mine has been removed. I have the efi or mpi system I am pretty sure, is this one limited?
 
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alldodge

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From my reading it should always be working, in gear or not. Only way to know is with a known accurate tachometer
 

Jgcrock99

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Pretty sure you don't want to rev over 5K in neutral.

I'm not saying I do I'm saying I could. My starting instructions are to lower the drive, crank it and then rev to wot and back off. When I do that I can hit 5k with room in the controller for more. But with drive engaged and trimmed appropriately I could max out at 4800 smooth or light chop. Now all of the sudden I can hit 5k if I'm not careful. I will be checking the tach for accuracy but my speed has increased as well which seems unlikely if it was a faulty tach. Seems like my rpms would increase but speed would remain the same. Just a very strange scenario. Boat still runs fine and drives great just an odd problem to come up
 
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H20Rat

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I'm not saying I do I'm saying I could. My starting instructions are to lower the drive, crank it and then rev to wot and back off. When I do that I can hit 5k with room in the controller for more.

Just going to be blunt and say this, but why would you do that? That is the WORST POSSIBLE THING you could do to your engine and drive. Rev a cold engine to 5k? Might as well take a sledgehammer to it, less damage that way.

Starting instructions for your engine should be pump the throttle once or twice if cold, and turn the key. Nothing else.

(to be honest, you aren't alone... I have a neighbor who does the exact same to all of his boats. Revs it to the max instantly after starting for a second, never figured out why he doesn't like his engines very much, but he seems to keep a supply of new ones coming in)
 

Scott Danforth

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I'm not saying I do I'm saying I could. My starting instructions are to lower the drive, crank it and then rev to wot and back off. When I do that I can hit 5k with room in the controller for more. But with drive engaged and trimmed appropriately I could max out at 4800 smooth or light chop. Now all of the sudden I can hit 5k if I'm not careful. I will be checking the tach for accuracy but my speed has increased as well which seems unlikely if it was a faulty tach. Seems like my rpms would increase but speed would remain the same. Just a very strange scenario. Boat still runs fine and drives great just an odd problem to come up

You only need to bring the revs to about 1200-1500 rpm

Hitting 5k in neutral does nothing good

Check your tach
 
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