Low RPM @ WOT

madolive3

Petty Officer 2nd Class
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Sep 2, 2011
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120
I just bought a 1984 Century 3000. It's an 8 cylinder, I'm guessing that the motor is the 228 HP and not the 260hp. I can't find anything on the motor to indicate which engine it is. OMC V8 and those are the HP ratings for that year Century. The 3000 Sport model had the 260. I'm pretty sure mine is not the sport model.
I'm only getting an indicated rpm of about 2500 wot.
Having read the sticky about possible causes, I didn't see a defective Tach. Is this a possibility? Is there a way to test the Tach?
I'd like to eliminate that first.
Top end seems fine, it feels like I'm up around 40 or so. speedo topped out at 34 mph, but I think the speedo if off a bit, I'll get my GPS in there this weekend.
Sluggish to get on plane though. Any thoughts? Motor starts right up and sounds like it's revving way more than 2500 Rs. Thanks.
Edit, The current prop it a beat up 15x17.
 
Last edited:

jerryjerry05

Supreme Mariner
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May 7, 2008
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17,923
Sounds like the tach and speedo are off.
The speedo it's hooked to a pickup tube on the back of the boat.
Make sure it's down and the end isn't broken off.

They sell an item Called a Tiny Tach I bought one for 16$ on Amazon.
Make sure you get the one for a 4stroker.

Weight and trim position can dictate performance.
Don't put too many people on board.

The prop: get a new or fix that one.
 

southkogs

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Your drive is a Stringer 800 (should be full mechanical). On the engine itself somewhere - mine is on the starboard side rear motor mount - there is a tag that should read something like "574FTHRCRA 1984." That will identify exactly what you have.

Go with Jerry's advice, but add a couple of things in just to make sure: If you've not done so, change your upper, lower and intermediate gear case lube. Make sure you're not getting any water intrusion. In my experience the upper gear case is the one that'll leak the most.

Also, check your trim ... if you've got Select Trim, it'll be on the front of the engine - not on the drive, that's your tilt. If it's operating, then monkey with your trim a little on different runs and see what results you get. If it's not operating, then add that into your list of reasons things are a little "off." My trim system still isn't working right, but I've got the engine kinda' center on the trim and it works "okay."

That's a good size boat, so upper 30's to 40 MPH with that drive sounds good. You just wanna' make sure your RPMs are where they are supposed to be.
 

madolive3

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Sep 2, 2011
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Good stuff, I'll work with this and get back. I think the first this is verify revs and speed.
What is the trim? that sounds different than the outdrive tilt. I did experiment with the outdrive tilt, didn't help much.
Thanks
 

southkogs

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Your boat may not have trim ... though I would think a Century would.

Tilt is the motor and quadrant gear on your stern drive that lifts the drive up for trailering. The Stringer is designed to operate with the drive tilted all the way down. You can tilt up in shallows if you have to, but limit it to short distances and low RPMs (think "no wake" only). Trying to run with your drive tilted up will mess up your ball gears and clutch pack ... if nothing else.

Trim is either a jackscrew or hydraulic unit on the front of your engine. It adjusts the attitude of the stern drive relative to the boat and water surface. Adjusting the trim can help you come out of the water faster, and then trimming again helps the boat plane out more efficiently. The Stringer didn't necessarily come with trim, so it's possible that you don't have it.
 

madolive3

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Sep 2, 2011
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Thanks. I don't see anything like that in the engine bay. I don't think I have one.
Well I can say for sure it's not full of water soaked foam, so it's not a weight issue
 

southkogs

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40 MPH is nothing to sneeze at with your setup. You may be fine.
 

madolive3

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Sep 2, 2011
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Turns out that I have a hydaulic trim. I got under and had to figure out how to get a new transom seal on. The trim worked for a second, and now I only hear the soliniod click. I'm hoping it's only low on fluid. I can't find the fill location for it though.
 

madolive3

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Sep 2, 2011
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Ok, worked all weekend out in the sun and heat. Ed my neighbor, and just about the best neighbor a guy could have, helped me.
Changed the Transom seal among other things. Found the Trim system. Fluid is full, I have to tap on the motor to get the trim to work some times. I think I need to rebuild the motor. I have a mini tach and I wired a working 12 outlet for my GPS, so I'll be able to get accurate RPM and speed readings. Might be next weekend before I can get on the water though. I'll keep this thread alive and post results. Thanks again.
 

madolive3

Petty Officer 2nd Class
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Sep 2, 2011
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120
I'm going to close this. My Tach is way off. I'm running 39mph as per GPS, my Rs are 2900, no way. I'll get my tach replaced and go from there, Thanks everyone.
 
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