[Slash9point5]

Hello Fellow MOC Members,

I have attempted to solve this issue with the help of all the great materials on this site, however, I am still in search of an answer. I have a 1995 Barchetta with a Mercruiser Alpha 1 v6 that I purchased this spring. A stainless steel 3-blade prop was installed by the previous owner with a 21" pitch and a 14.25" diameter. We have had the boat out 6 times and have loved the time on the water.

The problem we are having is that when I start to bring the boat to WOT, we get RPMs on the gauge up to 5800 and speed around 45mph (spedo not GPS). I only have briefly ran the motor at that rate to try and see what speed we are hitting and I still have not fully opened up the throttle because I am aware that recommended WOT is 4400 to 4800.

So far with the help of this site I have verified:

A) the tachometer dial behind the gauge is set to a v6 engine (#2)

B) the prop size and pitch is what most people with this set up use

C) 5800 rpms at WOT is way too high

So, I am trying to figure out if:

1) I should increase the pitch (23" would seem very high for a v6 4.3L)

2) or how I can verify if the tachometer is bad

3) or if the prop has some form of issue, even though everything looks to be shaped correctly.

The last piece of info I have is that the outdrive gear ratio is 1.84.

I appreciate any help that you can provide to identify the cause of this over revving.

Thank you and have a great day,

Kris

[IowaWing]

It sounds like a "spun" hub in the propeller to me.

The problem should be getting worse every time you run it. You should be seeing higher RPMs and slower speeds as it gets worse.

See if you can borrow another prop from someone that is just like the one you have now. A lot of people have spares just in case this happens.

[mikeyt]

I dunno, i suspect a problem with the tachometer rather than the prop. A 21" prop on the 4.3L would struggle to get over the 4800rpm mark and i think the rev limiter would kick in long before the engine got anywhere near 5800rpms. The 21" prop will work on the 4.3L but its more of a cruising prop so there wont be much grunt out of the hole but it should hit 50mph at top end.

See if you local boat mechanic has a used tach that you can swap out?

[SEMIJim]

I would think a spun prop would manifest itself just getting out of the hole.

Btw: We're running a 14x23 prop on our '94 182 Barchetta with the 4.3L MerCruiser V6, 4 bbl. carb and she runs fine. Good hole shot and, IIRC, 45 MPH at 4800 RPM WOT.

Jim

[IowaWing]

After rereading the original post, I now agree that it seems like an inaccurate reading on the tach. It would not be a bad idea to switch out the prop just to be sure. (If you can borrow one.)

[Slash9point5]

Thank you for all the quick response.

I was leaning towards the tachometer as well, considering the rev limiter would most likely kick in (unless there is a problem with the limiter).

However, since I bet I can borrow a used propeller easier than a used tachometer, I will probably try to eliminate the spun prop first.

Are there any other easy methods to verify the tach is bad?

And if the prop was spun would the boat drive as well as it does (on plane in 2 to 4 seconds, top speed almost 45 mph)?

Thanks again and have a great day,

Kris

[SEMIJim]

Originally Posted by Slash9point5

And if the prop was spun would the boat drive as well as it does (on plane in 2 to 4 seconds, top speed almost 45 mph)?

I wouldn't think so.

I would try switching the tach's number-of-cylinders switch between its proper setting and the others several times. Perhaps the switch's contacts are a bit corroded and that'll wipe the corrosion and get it working right again. (Then again: Maybe it'll just kill it entirely. You pays your nickel and you takes your chance.)

Jim

[mikeyt]

Originally Posted by SEMIJim

I would think a spun prop would manifest itself just getting out of the hole.

Btw: We're running a 14x23 prop on our '94 182 Barchetta with the 4.3L MerCruiser V6, 4 bbl. carb and she runs fine. Good hole shot and, IIRC, 45 MPH at 4800 RPM WOT.

Jim

Just goes to show that the same prop on two similar boats wont necessarily perform the same. I'm running a 20" 4 blade and hit 48 at 4850rpm on my '96 - 180. The 21" 3 blade i had before would give me 50-51mph at 4600rpm but didn't like to pull my wakeboarding kid out of the hole.

btw...i agree with the spinning of the little dial on the back of the tach. Corrosion can be a problem with them.

[SEMIJim]

Originally Posted by mikeyt

The 21" 3 blade i had before would give me 50-51mph at 4600rpm but didn't like to pull my wakeboarding kid out of the hole.

Fascinating. And we're running a 23" pitch.

When I wrote "Good hole shot" I might've been exaggerating a bit. It seems good to me, and the couple of different people we've had on the boat thought she planed-out quickly, but it certainly takes longer than "2-4 seconds" - at least if there's more than two of us aboard.

Then again: She's got a newly re-manufactured engine, just broke the 1st break-in period at the end of last season (we haven't had her out yet this season--it's a long story that includes re-upholstering), so in coming up to plane I don't think I ever once went WOT.

As for the top end: I can probably expect that to increase some as the engine finishes breaking in.

Jim

[Slash9point5]

To update this thread:

I had the boat out on Wednesday night for a little wakeboarding and was ready to rotate the dial behind the tach.

However, when I was parking the trailer, my wife went out for a quick spin and at one point she said she "turned hard and she heard a bang noise and the engine shut off and would not start for 3 minutes." At that point she was also in the middle of the lake and the depth finder was reading in the 30's.

It then started just fine and she picked me up.

We were a little tentative at first, but everything seemed to be working fine and I took her to WOT and magically, the RPMs were back to within operating range (4800 as opposed to 5800). The real interesting part is that now when we are on plane we have some spray coming from the back of our boat exactly as was described by Paul F in the following post:

Wake of my boat.

So, I don't really know what this means, but we wakeboarded for almost an hour with normal operation (rpms good, temp good, etc.) except for that spray which may be normal according to the above thread?!?

Also potentially of note, it may be my poor recollection, but before Wednesday's 3 minute incident, the boat always started in roughly 2-4 seconds of cranking...but now it seems like it is only 1-2 seconds. I would imagine this is either inaccurate observations on my part, or some other unrelated issue.

Thank you all for your time,

Kris