Tach line for 1970 80hp Merc?

I will be picking up this outboard(with a 16' Starcraft SS) in the next week or two and I'm curious if there is a tach hookup?

It also came with a CMC tilt/trim bracket, can I hook up a gauge for that?

Also any other insight on this particular OB would be appreciated. The seller started it up for me(video of that in the link for the starcraft below) and she went into gear running on muffs.

He says it is idling down under a load, maybe issues that tuning would eradicate? I have a marine mechanic that will be taking a look also, but not if I can fix this myself first

Thanks

Re: Tach line for 1970 80hp Merc?

Nice looking package Huron Angler. Good deals around off season.

I have three of those same motors, one runner and two for parts since parts are expensive and getting harder to find. Really grown to like this beast. A little temperamental to start cold (all those vintage inline are the same) but runs strong. Really love the unique sound these motors have. The one thing to look for is the condition of the internal wiring. If it has not yet been replaced, then it will have to be done. The insulation just crumbles and falls off the wires.

There is a connection for a tach hookup. Located on the starter side of the switchbox will be 4 terminals. Brown, white, red, green. The Brown terminal and wire on the switchbox is the tach connection point. That same brown wire runs up to the MerControl box in the wire harness. From there you will need a tach harness to plug into the connector on the front of the MerControl box to run to the dash.

If you buy a current style tach (not 1970's vintage) then you will need to remove the brown wire from the switchbox terminal and connect it to either of the yellow stator wires on the rectifier. There will be no connection then on the brown terminal on the switchbox.

First thing I would do to get an overall indication of the health of that motor would be to do a compression check.

Re: Tach line for 1970 80hp Merc?

Hey Moody Blue thanks for the info! I really hope the compression is good on this old Merc, that will be high on my list of things to do after dragging her home.

So would you recommend getting a vintage tach? Sounds like the way to go if I can find one in good condition. Several folks have advised me to go ahead and buy one or more "parts" motors to keep on hand. I should be able to find a few in non-running condition cheap.

What kind of performance have you gotten with the 80hp? I've been told that I should see 35-45mph with this setup if she's runs strong.

Also do you run the original 2-bladed prop? That's what mine has spinning on her as seen in the video.

Thanks again

Re: Tach line for 1970 80hp Merc?

I would (and did) get the style of tach you want. No big deal switching the wire around. Get one that reads to 6000. No need for the 7000 or 8000 range with that motor.

I have a heavy (1200 Ib) 16ft deep V fiberglass boat that will run 32MPH with two adults on board. I have the two blade prop as a spare and run a three blade prop. I find with my boat that a 17" pitch prop works perfect. Good acceleration for pulling skiers up and runs 5200rpm at WOT. A little high but I don't push it that far. I suspect with a 19" pitch I would run 35mph and 5000 rpm at WOT (perfect) but I'd rather have the low end torque and less speed.

Re: Tach line for 1970 80hp Merc?

I have a 71 Merc 800 on my 67 16ft Glaspar Avalon she runs pretty good, I get 30mph with 2-3 people. But mine sat in a garage for 25 years I just went through the basics and took it out this past weekend. Looking at putting in a tach as well.

Re: Tach line for 1970 80hp Merc?

Moody Blue I will be happy if my boat achieves those speeds and considering it's aluminum and lighter maybe even faster...but I need to get the motor tuned up and make sure she's all set before i worry about that.

I would agree that highest top speed isn't the priority, since for waterskiing a good hole shot is required, thanks for the info on the props.

How does the 2-bladed perform compared to the 3? Also is your 3-bladed aluminum or SS?


rspar I'm glad to hear she's running well for ya

I hope to get some good use out of this one too. It's nice to know folks are running similar outboards with success.