Mercury 150 BlackMax Questions

"Just recently bought a boat w

"Just recently bought a boat with a Mercury BlackMax 150 and I have a few questions, New to Boat Ownership..

1. What year is this outboat serial number tag
says 6617130?

2. Motor is slightly difficult to start hot or
cold?

3. Water Pressure gauge read 1-2 psi at idle and
13-15 psi at Full Throttle, nothing is coming
out of my tell tail P hole, what should I do?

4. What is the oil/fuel mix for this outboard?

5. What is the max rpms?

6. The previous owner has replaced the pro, what
should the prop pitch be for this outboard?

7. Is there anything that I should know about
this outboard good/bad, pros/cons??

Thank you for all the help


o yeah

8. Where could I find a new tilt/trim motor
preferably an OEM??"

"Bryan, so many questions [img

"Bryan, so many questions - will just warn you in advance, my answer may be a little long...

First off, that is a 1985 "XR2" model.

Many parts are still available from a Merc dealer.

Unfortunately, the t/t pump motor (and most of the assembly) has been long discontinued. You could however, retrofit a later model design, but will likely require changing the entire unit, not simply bolting on another trim motor.

Since the motor is about 25 years old you have to assume that at some point over all those years it may have been neglected.

Did you have the motor checked at all before or immediately after purchase?

At minimum I would have a compression and leak down test done on the cylinders. Pressure test the lower unit.

Unless you have "proof" of service, change the spark plugs, the impeller and lower unit gear oil.

The hard starts could simply be old plugs or old gas or could be a warning of a clog developing in the carbs or a fuel pump on the way out.

Oil mix - this model originally had oil injection. Is it still there? is it functioning? a marine tech will also be able to advise on that.

If you don't know, then run it at a 50:1 mix until you can confirm.

Your water pressure sounds ok and if the motor is not overheating your tell tale could simply be blocked (bugs like to make homes in any opening).

Your max rpms is 5500, you need to select a prop that will allow you to get to 5300 rpms (give or take 50 or so) when you are using the boat as you normally will.

That means "loaded" the way you will use it. The prop could be significantly different from what the previous owner required.

You may run heavier or lighter, in different water conditions - may "cruise" more than run flat out. Those and numerous other differences will dictate what you should run so you need to do some trial/error testing.

Each 1" change in pitch will result in a change of approx 200 rpms - so load up and take her out (when the motor issues have been addressed and she is tuned up).

If she will only get to 5000 rpms then go with 1-2" less in pitch - if it gets to 5600, move up 1" in pitch etc...

This was a decent motor in it's day and it could well have many many more years of life in it yet.

The basic design stayed in production for many years finally ending it's lifespan as the 135 Merc (the 135 and some 150 models shared Merc's 2.0 liter powerhead until production ended about 5 years ago) which is why there is still excellent parts support through Merc.

Should it require it, this motor is an excellent candidate for a refurb or rebuild.

That may not be something you considered when you bought it (the requirement for a rebuild) but you have to consider, since it is 25 years old it may be "tired".

If you are mechanically inclined it can be done for about 1000 bucks - a shop will charge about 2500. But when you compare that to the cost of a new 150 (12K or better), that could be a cheap way to get 15-25 more years from the motor...."

"Thank so much for all the in

"Thank so much for all the in site.
I'm a certified Toyota Tech, so I have a little mechanical abiliy. at leat I hope.

So if my water pressure is ok that is if my pressure gauge is correct and there is no water coming out my tell tail is there another spot for the water to exit the outboard?

what would a good compression pressure reading be for this old of motor.

I dont see any where to add oil on the outboard, there looks like there was a spot for a resivor at one time but is no longer there.

it is not a XR2 at least I dont see anything on the cowling or anywhere else that would indicate that.

So the outboard is a 1985 also

Should I buy a factory repair manual from merc
or would an aftermarket work, I dont even know why I asked that I would never use an am manual working on a toyota.


Agian Thank you SO SO Much"

"Most of the cooling water goe

"Most of the cooling water goes right down the exhaust and out through the prop (along with the exhaust) acting as a muffler in the process.

Some models have a tell-tale, others simply have a relief hole which spits or drizzles water mostly for the benefit of the operator to let them know the water pump is functioning.

Anything above about 100 psi would be good and personally I would consider anything above 90 to be fine as long as all cylinders are withing 15 psi of each other (the book say 10-15% but some recent guidance from OMC/BRP suggests 20% is fine).

A leakdown test would give you a better indication of how the rings are holding up - they would be my one concern - after 25 years I would expect them to be suffering from fatigue.

Personally, I would pull the heads and get a look inside (head gaskets are relatively cheap). If there is even a hint of scoring on the walls I would have it honed out and re-ring it at minimum.

And yes, it would have had an on-board oil resevoir - so if it's gone mix at 50:1 - you can use TCW3 rated "dino-oil" or even a semi-synthetic. I personally wouldn't waste the money on fully sythetic oil (but you will get varying opinions on that here as well).

A Seloc's manual at 35 bucks is worth having around just for reference..."

"Well i took the boat out toda

"Well i took the boat out today, got the tell tail water to P, great. The prop says 23m on it. it runs at 4500 rpm at WOT at about 40mph that is with my trim not working and the bow in the water. It should be differnt when I get the trim working and the bow picked up. What type of plugs do you recomend?
I have been mixing it at 50:1, Because I just remeber my dad mixing his at 50:1 when I was a kid. Again thank you so much


Bryan"