1986 75 HP Questions

[wannagofishin]

I just got a 1986 75hp 4 cylinder Merc that runs and looks like new. I don't have a manual yet and I will get one, but in the mean time, I just have a couple of questions about it. First, I'd like to add a trim indicator. I think the sending unit is at the bottom of the swivel bracket. If it is, I need to know how to hook it up. If it isn't, what is it? There is a wire to ground and another short piece going nowhere. It looks like it's plugged.<br /><br />Second, I'd like to add a tach. In the searches I've done here, I read about a harness I can get. Does anyone know where I can get one and is it necessary? I do a decent job of wiring, but if there is a better way ...<br /><br />Third, anyone out there have a manual they don't need any more? I don't want a Seloc (what a waste of money) or any other multi-year/model manual.<br /><br />Thanks,<br /><br />Dan

 

[AMD Rules]

Re: 1986 75 HP Questions

The trim sender is typically mounted on the end of the swivel pin, on the port side of the transom bracket. You will see one ground wire terminating there, and one sending wire. That sending wire should hook into your control harness at the motor.<br /><br />Spend the bucks on the proper harness to run from your helm control to your console guages. It will have the wires needed for both your tach and your trim indicator. They are available from your local Mercury dealer. Wiring it yourself is an option, but it is a lot easier to use the factory harness.<br /><br />Can't help you with the manual. Sorry.

 

[SeaKaye12]

Re: 1986 75 HP Questions

Keep checking e-bay. First though...get the part number for your manual. That way you can be sure you're getting the right one.<br /><br />I found mine for my 850 for $15.00. The seller didn't list it very well...and nobody noticed it up there. I bought it on a "buy it now".<br /><br />I have the Seloc also...and I would agree....it's certainly better than nothing...and may just answer the one question that would make it worth it's price...but the factory manual is far better.<br /><br />Even then...the pictures leave a lot to be desired...in this age of beautiful razor-sharp on-screen color photographs like the people here on i-boats furnish....<br /><br />I agree with AMD Rules re: getting the tach harness....but in reality there's only three wires to a tach (well...four if you count the bulb 12v source...)<br /><br />One is 12V (ignition on only); one is ground...and the third is to the rectifier on the engine. The first two are probably up in the helm area already...and the one wire back to the engine is a breeze...maybe just on a temporary basis.<br /><br />Good luck..sounds like you have an un-molested older engine. That's pretty nice. My '77 850 is like that too...never been apart...never been messed with... It makes for far fewer puzzles to figure out as you go along.<br /><br />Thanks for reading, Chuck

 

[wannagofishin]

Re: 1986 75 HP Questions

Thanks for the answers guys. I took her out today for the first time. This engine is on a 1986 Skeeter Strada F-80 15' Bass boat. With just me and a few items in the boat, I got 37.9 mph @ WOT according to my GPS. I REALLY want a tach. The prop is a Quicksilver Stainless Steel 17P and the original is aluminum, also 17P. It seems to me that 75 HP and such a small boat, it should run a bit (at least 5-10 mph) faster. Am I asking too much from this engine? <br /><br />Also, at idle speed, around 6 mph give or take a few mph, the boat zig-zags. It constantly needs course correction. It has an SE Sport 300 Hydrofoil on it. Could this cause the problem? Or is my trim incorrect? Something else?<br /><br />Speaking of steering. . . from dead straight to full left or right turn, it doesn't seem to turn as sharp as my little Merc 25. It takes a mile and an acre to hang a U-turn. Any way I can adjust this? Haven't had a cahnce to look at it yet but thought maybe someone could tell if it can be changed and how to do it.<br /><br />Thanks again,<br />Dan

 

[dieselcat]

Re: 1986 75 HP Questions

I had an 86 75hp merc on a landau pro 17 Aluminum bass boat, with a 13.125 X 19 pich stainless prop and going down river i would hit 43 MPH,measured by GPS.That was with 3 people in the boat,at somewhere between 5400-5600 rpm's.Never had it on a still body of water,but that is probably about right.I'm sure you could step up to a 19 or even a 21 pitch with your boat.
I'm not an expert by any means but i do know that for every inch of pitch you go up your rpm's go down about 200.So if your getting 5900 rpm now with your 17,and you put a 19 then you will now be running roughly 5700 rpm.I think that motor's WOT [wide open throttle] is 5500-6000.Someone correct me if i'm wrong?Hope this helps