1978 Black Max 1500 Motor HELP!!!

[jwayte]

I recently bouth an older 18 ft. Skeeter bass boat with an older Mercury Black Max 1500 150hp V6 motor. This is my first boat and I bought it all for only $1500. That being said and me not knowing much about them, I could use some help with some things. I have had the carbs pulled out and rebuilt. I also had wiring repaired for the electric trim/tilt. She starts up but runs rough. A jumpy idle. I used her about 10 times last summer and she gets out of the hole slow, mostly, and tops out at about 47mph WOT and only about 4700RPM. This seems slow and low. I just recently took her out of winter storage and started her up. It started but the prop seems like it struggling to turn and makes a whinig noise. Sounds like a bearing. I am good mechanicaly with autos but new with bouts. Could someone give me some advice other that the obvious and take it to a bout mechanic. Also, the speedometer on the boat has an air tube connected to it and works when air is blow through. I know where the hole is on the front of the lower unit but there is no fitting to connect the tube.

 

[kadesdad07]

Re: 1978 Black Max 1500 Motor HELP!!!

The best advice I can give is what I have finally done. First get you a repair manual for it. I thought I knew enough about mine, but I hate to admit I was wrong. It has helped me understand the mechanical side of my engine and outdrive to determine any problems.

 

[Chris1956]

Re: 1978 Black Max 1500 Motor HELP!!!

That motor has it's own repair section in my genuine Mercury Outboard Service manual. It is different than the 175HP V6, as well as the 150HPV6 of a later year, for some reason. I did not study that section, since I did not have that particular motor, but I know that Merc only made the motor for a year or so.

BTW - Start with the basics on your motor. Compression and Spark test. What size prop do yiou have on it? The correct range is likely 19-21" pitch.

 

[j_martin]

Re: 1978 Black Max 1500 Motor HELP!!!

Did you service the engine at all before you ran it last year?

It sounds like it might not have lube in the lower unit. It might have water in it. A mandatory fall service check is changing the lower unit lube, or at least examining it for water and metal.

If it won't go 5000 at WOT, something is seriously wrong.
some possibilities:
Ignition failure
Fuel failure
Lower unit failure
Wrong prop
Wrong engine mounting

Any of these can quickly mount up to serious, expensive damage. Maybe you're already there.

John

 

[jwayte]

Re: 1978 Black Max 1500 Motor HELP!!!

I did have it serviced and the carbs were pulled, cleaned and rebuilt by a local boat mechanic. The lowere unit was completely filled and the lube was good. I do however believe your statemwnt may correct in that I need to change the lowere unit lube after the winter. The current prop is a stainless steel one marked with a 23 degree pitgh. This might be the wrong size prop. I will bring it in for another service check. Is it difficult to change the lower unit oil? I am ordering a manual today. What is the best manual to get?

 

[Faztbullet]

Re: 1978 Black Max 1500 Motor HELP!!!

Check compression, I going to guess its low. That setup should be about right on a Skeeter.If its low on all cylinders, do a decarbon and recheck

 

[j_martin]

Re: 1978 Black Max 1500 Motor HELP!!!

I did have it serviced and the carbs were pulled, cleaned and rebuilt by a local boat mechanic. The lowere unit was completely filled and the lube was good. I do however believe your statemwnt may correct in that I need to change the lowere unit lube after the winter. The current prop is a stainless steel one marked with a 23 degree pitgh. This might be the wrong size prop. I will bring it in for another service check. Is it difficult to change the lower unit oil? I am ordering a manual today. What is the best manual to get?

The time that the LU must be checked is before freeze in the fall. If it gets a little water in it, you may not know it. If the water remains in it over winter, it will freeze and break the lower unit, just like frozen water breaks motors and plumbing.


There are 2 screw plugs for the lower unit, one on the bottom of the bullet, and one near the top of the LU. Remove both and drain the fluid. Examine it for water. It should be clear or maybe black, but not milky.

Get a quart of Mercury lower unit lube. Either will work, but I use High performance just for insurance. Walmart has a pumper that will fit the quart bottle and screw into the lower (drain) hole on the LU. Fill the LU by pumping it into the lower hole till it comes out the top. Put the top plug in, and remove the pump from the lower hole, spilling an ounce of fluid, and put in the plug. (there needs to be a little air space over the fluid, so don't fret about losing a little. You should.) Be sure to use new gaskets on the plugs.

I'd use the genuine Mercury manual for details, and a cd manual I bought online for a bigger picture of similar motors.

hope it helps
John

 

[jwayte]

Re: 1978 Black Max 1500 Motor HELP!!!

Thanks for the help. Sure enough the lower unit was out of oil. I ran about a half quart through, cleaned and drained it. No metal on the little magnet. Refilled with the kit you mentioned and it seems to have done the job. Will let you know. What is the best way to decarb the cylanders? Can I use Sea Foam or is there another way?

 

[CharlieB]

Re: 1978 Black Max 1500 Motor HELP!!!

Before you launch her get ahold of a spark tester and verify your ignition system is fully functioning, one dead cyl and your performance will seriously fall off, that boat and motor combo should jump out of the water and run right around 55 mph in the area of 5600 rpm at WOT.

A 23 pitch may be correct, don't start changing anything until you verify all cylinders are running.

 

[j_martin]

Re: 1978 Black Max 1500 Motor HELP!!!

Thanks for the help. Sure enough the lower unit was out of oil. I ran about a half quart through, cleaned and drained it. No metal on the little magnet. Refilled with the kit you mentioned and it seems to have done the job. Will let you know. What is the best way to decarb the cylanders? Can I use Sea Foam or is there another way?

There's a link in the sticky forum here that explains how to mix up some seafoam and fuel in a pony tank and run it through. it's tough on neighbors, but it does the engine real good.

Keep a real close eye on the lower. At the first indication of failure, fix it. It's a 4 1/4 inch lower, where most on an engine that size are 4 3/4. It peps up performance, but if anything fails, it usually will put the pinion right out the side.

If yours takes the larger prop, the above scenerio has already happened.

hope it helps
John

 

[jwayte]

Re: 1978 Black Max 1500 Motor HELP!!!

I went out and bought a can of Seafoam. will do it this weekend. It is supposed to be nice. I would prefer running it through my main tank though. Not buyind a smaller prtable tank would be easier. Can anyone give detail example of how to run Seafoam through main 12 gallon tank? Thank you

 

[ddennis]

Re: 1978 Black Max 1500 Motor HELP!!!

You can't do a proper decarb on an engine that way. You need a smaller tank to run a high concentration of seafoam to fuel through. You don't want to run it that high for that long through the main fuel tank.

Anything worth doing is worth the time taken to do it right.

 

[j_martin]

Re: 1978 Black Max 1500 Motor HELP!!!

I went out and bought a can of Seafoam. will do it this weekend. It is supposed to be nice. I would prefer running it through my main tank though. Not buyind a smaller prtable tank would be easier. Can anyone give detail example of how to run Seafoam through main 12 gallon tank? Thank you

The problem is you want to mix a can of sea foam with about a gallon of gas. That mixture will barely fire in the engine, run real smoky, and if run a long time probably hurt it. For a short time, it floods everything with this marvelous cleaning fluid called sea foam, which is the goal.

The technique involves wetting the engine down with the rich mixture of sea foam, then letting it sit for a bit while the sea foam loosens all the crud up, then running normal fuel/oil mix through it to clean it out. You can't efficiently do that combination without getting a pony tank.

If you're real cheap, you can get away with a siphon tube in a milk jug.

hope it helps
John

 

[jwayte]

Re: 1978 Black Max 1500 Motor HELP!!!

I will run through a pony tank. I think I will try to use a milk jug(empty) as suggested. I am prepared for smoke. Any other suggestions. I really want to clean this motor and get a smoother idle and better performance. I tink there is alot of carbon buildup.

 

[jwayte]

Re: 1978 Black Max 1500 Motor HELP!!!

I pulled carb covers and sprayed Seafoam into inlets as well as sprayed into plug holes and let it sit over nite. I then ran a gallon of gas with foam mixture in a milk jug. Smoked a bit but now is running much smoother and nicer. Will run on water and open her up to clean out more thoroughly. Thanks for helo. I am getting thier quickly through "Baptism B Fire. Thanks for the experience and help my friends!