1984 Mercury Black Max boggs out under load

[GITDNET]

Hello everybody.... I'm new to this site and have some problems with my 1984 Mercury 150 Black Max... I recently bought this boat and the first time I took it out it started fine, smoked a little bit and once I started to accelerate it almost died, then I backed off a little and then slowly accelerated and it took a few seconds to kick in and really go... after a couple runs it progressively got worse to where it would just bog out when accelerating. I rebuilt the carbs and adjusted the floats, all the jets seemed fine, broke down the oil pump and cleaned it (oil injection) checked the fuel pump and filter, everything good, checked compression, O.K., I hooked it up to the garden hose and seemed to run great. Took it out to the lake and ran like CRAP!!! would not Idle vrey good and could not accelerate not even in neutral... What the heck could it be???? All of your input would be greatly appreciated.... Thanks, GITDNET

 

[lots of boats]

Re: 1984 Mercury Black Max boggs out under load

Hi
I had several 1986 150 mercs, I don't know if they were the same as yours, but I ran twins, and one of the motors ran poorly sometimes. I did all the standard clean, drain and trouble shoot, had the dealer help and nothing fixed if.

Next I moved all the carbs from one engine to the other and the problem went with them. Next I moved the carbs one at a time and found the culprit. Pure farmer technique.

The next step was to buy a new carb but before I did that I took it apart one last time and really looked at it. There was a tiny piece of plastic film in one of the pasages, it worked like a check valve under high fuel draw.

I doubt this is your problem, but just wanted to let you know that sometimes some small thing is overlooked. Good luck.

 

[j_martin]

Re: 1984 Mercury Black Max boggs out under load

Fuel pump, or a small leak in the fuel line between the engine and the tank.


John

 

[GITDNET]

Re: 1984 Mercury Black Max boggs out under load

Hey thanks alot for your input...I took it out again yesterday after I checked the float adjustment which was off on all three carbs now it idles great and I can accelerate in neutral to WOT. So after feeling confident I put it in gear and started to accelerate and same ol crap it bogged out. So when I got home I started to go through the fuel lines from the main fuel tank and the line from the mail fuel tank that I use all the time went to a tank selector switch and noticed gas was leaking at that connection, so I bypassed the selector and ran the fuel line directly to the primer bulb.. Now it's monday and I have to wait until the weekend to get it on the water...

 

[olemerc115]

Re: 1984 Mercury Black Max boggs out under load

I feel your pain I bought a bass boat with a 81 merc 115 inline 6 on it, my motor does exactly like yours I do this and that to it and randomly it will bog down, is it just me or is it just that all these older mercury engines just unreliable junk, I have tinkered with mine a month still does the same old thing, the guy sold it too me couldnt fix it either, there are many many threads in here with old mercs doing this very common problem, do the johnson and evinrude motors do this too, I just wondered, because this is ridiculous, I am too going to change myfuel lines from both tanks to the manual selector, just to see, but it seems like everybody says rebuild the carbs and when we do it is still broke, I want to fix me problem not throw money at it take the time to rebuild all three carbs, rebuild the fuel pump and still havethis problem, I just dontunderstand why all these old mercs do this just some real finicky engines if yoiu ask me, I guess I will learn as I go if I dony grow crazy first, good luck to you and PLEASE keep us posted nobdy in my home town or near it knows al lot about these old mercs so this is the best resourcefor info I have found this forum and thepeople posting here aregreat thanks again

 

[j_martin]

Re: 1984 Mercury Black Max boggs out under load

A two cycle engine goes squish, bang. It's pretty simple compared to some of the modern engines we have to contend with.

If it gets fuel, has compression, and gets good spark at the right time, it's gotta run.

If it has trouble at a certain speed, it's missing one of the above at that speed.

If the engine has good compression, everything else on this thing is relatively straightforward. The only problem is the parts can be pricey, so testing and gaugeing is the way to find out what needs replacing. It's really not that difficult, but get a manual and go by the book.

When I bought my XR4, it had about a dozen misadjustments or wrong parts, or unfixed troubles in it. Now that this 20 year old motor has been properly looked after, which took taking the reed plate off and inspecting things, rebuilding the carbs, and pretty much overhauling the entire fuel system, it idles as long as I need it to, and goes like a bat out of **** when I can it.

There ain't much on the lake can touch it. It ain't junk fer sure.

hope it helps
John

 

[CharlieB]

Re: 1984 Mercury Black Max boggs out under load

What the old Mercs do NOT have is an accelerator pump.

Idle mixture MUST BE fat enough to allow acceleration under load.

Adjust idle mixture IN GEAR IN THE WATER to best idle speed, then reset idle speed by linkage position.

From in gear at idle, swiftly open throttle WOT and observe engine for hesitation, bog, lean sneeze or cough. If ANY then add idle fuel 1/8 turn on each cylinder, retest until all trace of hesitation is gone.

 

[jscgdunn@telus.net]

Re: 1984 Mercury Black Max boggs out under load

Boat balance is another thing to check. With my boat if it is loaded too heavy in aft, it will bog as well....the "old potato in exhaust pipe". I moved battery to front of boat....problem solved.

 

[j_martin]

Re: 1984 Mercury Black Max boggs out under load

Another thought is that this motor likes a ventilated prop if it has to push hard to get going. The vents allow some exhaust gas to break the traction of the prop, allowing the engine to spool up to the power band. As forward speed increases, the water flow closes the vents.

hope it helps,
John

 

[1984Fabuglas]

Re: 1984 Mercury Black Max boggs out under load

I have the same problem with the same motor.
Going to replace the stater and thinking maybe reed valves?

Did you ever get yours running?