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1979 mercury black max 150hp issues

R

Reeder

New member
Bought a 1979 ranger bass boat with a 1979 mercury black max 150hp v6 motor.

main symptom is not wanting to rev up to full rpm. Boat won’t plane out. Doesn’t happen every time but when it does, pulling back to idle causes the engine to die. Then starter solenoid won’t lift teeth. Have to manually lift teeth once, then will fire.

the idle seems a little rough and the not coming up to full rpm seems to happen after extended idle time.

I cleaned and inspected all carbs. No evidence of trash, jets clear, no evidence of water, butterflies all sinked together, floats seems to work, needles clean. Reeds show no damage or evidence of heat (checked without removing them. Just visual inspect while carbs off)

cant find a fuel adjustment screw. Only a mention of an air bleed screw in the manual. Haven’t adjusted that in any way yet.

fuel was brand new, can of sea foam run after initial test on lake. Problem persisted intermittently. Replaced two spark plugs (all they had that day).

where should I look now?

fuel pump? Enricher valve? Adjustment of some kind? Stator?

any tests/suggestions/direction would be greatly appreciated.

thanks in advance

s/n for motor 6181979
150hp
mercury black max outboard
1979 year
v6
 
Thanks for the suggestion. I forgot to mention that I compression checked all 6 cylinders prior to purchase. All were 70-72. Without being able to locate a standard, I took it as good news that they were all so close together.

what is the recommended method for checking spark? I’m handy but not a gear head so to speak.
 
Update- I did some more research. I tested the enrichner valve. Seems to work fine. I retested the compression and got the same 70-73 psi. I did a crude fuel pump test and it passed. So here is my thought process (and help me if I’m wrong)

when I looked up the carbs trying to find adjustment/mixture screws...I found out that there are none. It is done with changing jets. And several posts said that you would need a big change in compression to make that necessary.

compression test videos for all 150 hp motors I saw were all above 100 (as faztbullet pointed out). So do you believe my inability to consistently get the motor to rev up rpm’s enough to get on plane and go is a carb jet issue caused by low compression?

And if so, should I consider a cylinder/ring/sleeve rebuild?

thanks again for all the advice

carb1374-5427 wh-23-1

i can provide jet sizes if that helps
 
If compression is actually that low when you try to plane at throttle the mixture will be overlay rich as fuel/air ratio is off..lazy out of hole and bogging. Once broke over compression will build slightly and it will see to run OK at WOT but be less than expected performer. If it needs rebuilt don't waste your $$ on it..Sell it as is and add money you was going to send rebuilding and get a 2.4 or 2.5 150
 
I plan to use a different compression gauge to test it, also going to order a new fuel pump, and fuel filter/water separator. Going to drain the fuel tanks, inspect the fuel pick up and tanks. Will also get a small plastic tank and test that on the motor also. Side note, I’ve never been able to get it to bog down while testing on land with the muffs. Only under strain while in the water.
will update with my findings
 
I’ve never been able to get it to bog down while testing on land with the muffs.​
Click to expand...
That because engine ha no load or backpressure. They will sound and rev up fine on muff if only running on 3 cylinders!!!!
 
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