2006 Mercury 50hp 4stroke efi high rpm

[jc747]

Hello

I recently purchased a 2006 Lowe 160 stinger with subject motor.

At approx 5500 rpm the speedometer registers +/- 15 mph & boat does not fully plane out. This is with one person in boat.

Attempts to improve attitude, trim, throttle, all result in RPM quickly jumping to 6000+ rpm even though motor sound does not indicate over-rev (in my humble opinion..).

Does this motor have over-rev alarm? I believe so but would like your opinion.
Could the tachometer be providiing false readings?

I am new to 4 stroke motors so difficult to relate RPM to motor sound..

Thanks in advance for you replies.

JC

 

[Texasmark]

Re: 2006 Mercury 50hp 4stroke efi high rpm

That's your first task is to determine if your instruments are being truthful. First indication of a condition like that otherwise would be a spun prop but you gave no indication as to hitting something that would strip it and surely on a new engine it would not have had time to wear out. Course the other thing would be to have someone hang a 15" lower unit engine on a 20" boat transom. Could that have happened?

At 6000 rpm your engine would be singing, not humming. Your ear can help you determine that. What is the history of the boat? Did you get a test drive B4 purchasing and how did it turn out? Where is the antivent plate with respect to the bottom of the transom with the boat sitting level and the engine vertical. What does the prop look like...dings, signs of rough usage? How about some pics of same and some side views taken at the lower 1/4 of the hull looking straight into the side of the boat/transom/engine with the engine positioned as I mentioned. Then with the engine tilted up, a picture of the prop from the rear looking right into the rear of it. We will go from there.

Mark

 

[jc747]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Thanks Mark.

Your comments are relevant and i thank you.

I spoke to the Mercury tech (Mercury certified) employed by dealer who sold me the boat. His opinion was the tachometer must not reflect actual motor RPM and suggested i adjust the tach.

Issue i struggle with is comparing the four stroke engine sound with more familiar two stroke equivalent. I am sports car enthusiast and place high value on tachometer readings so at this stage i will limp along until i confirm tachometer reading reflects actual motor RPM.

I did confirm prop resistance in CCW direction so no issue with hub/clutch.

Thanks again for taking time to respond.
James

 

[jc747]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Mark,

I attached photos of lower unit.

 

[Texasmark]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Mark,

I attached photos of lower unit.View attachment 145374View attachment 145375

That looks good. I'm going to go with the tach problem. Most tach's have a selector screw on the rear that sets them for the engine to which they are attached. If that screw is in the wrong position for your engine it could be the cause of your problems. Is the tach newly installed, or has anything changed from the prev owner?

I only rode in front of 1ea 4 stroke OB and it was a 4 cyl 55hp Homelite back in the early '60's It was extremely quiet as compared to 2 strokes of the day. I understand that there are "Tiny Tach" units available on Amazon or some www selling site that sell for a few bucks. I have one on my lawn mower so it can't cost much. The sense wire just wraps around a plug wire and then I assume it needs 12v and gnd to operate like any other electronic device. Before I went nuts worrying about things, I'd check the tach and if ok, get a tiny tach and verify your numbers.

Would appreciate feedback as to how this comes out.

Mark

 

[Jeep Man]

Re: 2006 Mercury 50hp 4stroke efi high rpm

JC, what size prop are you running? From the photos, it looks on the small side for a Bigfoot model. I have a 60 Bigfoot with a 14x11 prop, which is pretty much the standard for my motor.

 

[jc747]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Ray,

The prop is a 10 7/8 x 11p. I don't believe this is 'bigfoot' lower end.

Mark,
The gages appear to be OEM on the Lowe stinger 160. Will check out the 'tiny tach' option to help verify setting.

I removed the tach & trim gages (also working erratically) yesterday. The tach is set on 5P and merc tech tells me should be 6P..
Both gages are marked CE? Anyone know who mfgs these gages?

In addition to the cyl/pulse adjustment on tach, there is a knob on both units that may or may not be an adjustment? Of course, no markings..

Thanks again for your replies. Will let you know how it progresses.
JC

 

[Texasmark]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Ray,

The prop is a 10 7/8 x 11p. I don't believe this is 'bigfoot' lower end.

Mark,
The gages appear to be OEM on the Lowe stinger 160. Will check out the 'tiny tach' option to help verify setting.

I removed the tach & trim gages (also working erratically) yesterday. The tach is set on 5P and merc tech tells me should be 6P..
Both gages are marked CE? Anyone know who mfgs these gages?

In addition to the cyl/pulse adjustment on tach, there is a knob on both units that may or may not be an adjustment? Of course, no markings..

Thanks again for your replies. Will let you know how it progresses.
JC

The bigfoot is essentially a 90 hp lower unit like my engine. It turns a 13+ dia wheel. You don't have one

 

[Texasmark]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Ray,

The prop is a 10 7/8 x 11p. I don't believe this is 'bigfoot' lower end.

Mark,
The gages appear to be OEM on the Lowe stinger 160. Will check out the 'tiny tach' option to help verify setting.

I removed the tach & trim gages (also working erratically) yesterday. The tach is set on 5P and merc tech tells me should be 6P..
Both gages are marked CE? Anyone know who mfgs these gages?

In addition to the cyl/pulse adjustment on tach, there is a knob on both units that may or may not be an adjustment? Of course, no markings..

Thanks again for your replies. Will let you know how it progresses.
JC

Go to the Teleflex Morse www and look up "Outboard Engine Tachometers, 4 through 12 pole alternators". Explains what is on the back of the tach......their tach but others are probably similar. Don't know what CE stands for.

Here's a quick easy test. Your engine should idle in F gear in the water at 650 - 700 rpm. In N at the dock, that number would rise to maybe to 800-900. What does your tach read under these conditions? What you can do, if you don't know how many poles your alternator has is move the screw yourself to 6p like your tech said and read the meter. I don't know how many poles your alternator has. If you get the above readings right, then you must have the right number selected.

I have heard that current edition Mercs use the same number of poles in their alternators but I don't know what that number is. Apparently your tech does.

Mark

 

[jc747]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Thanks Mark.

One fact i believe established is options are one of two options: 3P/6C OR 6P.

As you suggest, my plan is to adjust to 6P and test this weekend. Regarding trim gauge, not high priority; will purchase new from a sponsor of the forum as soon as i solve tach issue.

i will post results here once confirmed should other members encounter similar issues.

Thanks again JC

 

[jc747]

Re: 2006 Mercury 50hp 4stroke efi high rpm

Case closed.

6P is correct setting for this motor.

Trim gauge still not working; plan to purchase new unit.

Thanks again for your help. JC