Something's not right here

John Gibbons

Recruit
Joined
Jul 7, 2019
Messages
4
I just purchased a used 2010 Tahoe Q4 SS (18') with a Mercruiser 4.3L (4 barrel) 190 hp. The market for used boats where I live is very competitive and there was no opportunity for a water test prior to purchase. It has what I believe to be the stock prop (3 blade aluminum, not sure of the pitch or size).

The boat has very poor performance though the engine seems to perform normally. When accelerating I have to rev up to to max RPM (4800) to get the boat on plane and it will only do about 21 mph when trimmed out at that RPM. I have to be careful not to over rev the engine as I hit 4800 RPM at roughly 3/4 throttle.

My initial suspicion was the prop but now I am thinking it might a damage hub or worse, something in the drive itself. I am looking for advice from anyone who has experience a similar issue or some guidance on how to figure out what the issue is.

Thanks
John
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,309
welcome aboard

first, verify your speed with a GPS, the dash speedos are notoriously inaccurate

next, what prop do you have on there. we cant help you much more than stating we need that information

it most likely isnt the drive, because if it was, it wouldnt last more than a few minutes

it could be your prop hub. take a sharpie and draw a line across the prop and the prop nut. go for a ride. if the line on the nut moves with respect to the line on the prop, you have an issue

it could also be your coupler.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
If motor, prop and coupler are found Ok, distribute deck load evenly as will be loaded and trim the motor for combo to ride parallel to water level once on plane, report new wot run rpm with said condition. Will be interesting to see which wot rpm the motor dials to go from there..

Happy Boating
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,590
You sure about engine as the Q4 was only offered with a 135hp from the brochures listed????
 

John Gibbons

Recruit
Joined
Jul 7, 2019
Messages
4
The prop is a 3 blade aluminum 14 1/4 x 21". I went into the local Bass Pro yesterday and they did search on my Hull ID. The boat originally came with a 3.0L 4 cylinder engine. Obviously someone replaced it with the 4.3L so now I don't know anything about my engine year. I pulled the boat out of water last night and brought it home so now I can't do the mark and run test to see if they hub has spun. I pulled the prop off and everything look normal the hub slides into the prop and I can't turn it by hand, it appears to be a Flo Torq II to me from what I can see online. I put the prop back on and put the boat in gear with the motor off. It would turn one way with a click but not the other at all.

If it's not the prop hub what's my next step?

Thanks
John
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Find out if the 4.3 in it is a Marine engine, or just any old Auto/Truck Engine from a Wrecker
 

John Gibbons

Recruit
Joined
Jul 7, 2019
Messages
4
I found the serial number plate on the engine last night and searched it online. The engine is a 1992 4.3 LX (4 barrel) so it is a real marine engine. At least now I can order parts for the engine issues.

I still don't have any idea how to try to resolve the drive issue. I had a good look that the drive unit last night, it is an Alpha One gen 2 with a 2.00 drive ratio. From all appearances it appears to be the original drive that came with boat and the 3.0L engine.

Faztbullet, or someone else could you please elaborate on changing the drive ratio???

Thanks
John
 

TunaFish389

Petty Officer 2nd Class
Joined
Apr 26, 2018
Messages
184
The gear ratio won't effect the issue you are having and there is no problem running your current set up once propped to wot rpms. The issue is you are getting 56% slip with your current set up. First step verify tach is reading properly and GPS speed. Check for prop hub slip or engine coupler slip.

Once you get the slip under control running a 2 higher pitch prop will make up for the difference in gear ratio. If the 1.81 takes 21p to run at wot rpms then the 2.0 will be 23p for similar results.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
TF,

Plainly in agreement, gear ratio is relative, a matter to play with correct prop pitches till motor achieves it's max wot revs as loaded...

Happy Boating
 
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