1991 Black Max 135 Occasional Hole Shot BOG

[ReidMarsh]

I am hoping there may be some input to this minor situation I have discovered. I have a 1988 Edson Avanti 17 with a 1991 Mercury Black Max 135 and the Prop is a Laser II 21P. The engine overall has been really well maintained and is clean as a whistle, starts up cold or hot as expected without issues for the most part and would consider the engine to be "Excellent" condition if I had to rate it.

Last summer I had noticed that upon occasion, not very often... the boat would BOG on the hole shot, with only myself, but once up and running was smooth as ever, the guages all look good and never misses a beat. When I would try pulling one of the kids skiing (100 lbs), I noticed I was running into the BOG each and every hole shot, and would have to feather the throttle up making a slow tough pull on them. I considered the prop but seems to be a pretty good overall performer and as mentioned gets up and goes more often than not without issue.

I run SHELL V Power (no ethanol), use Shell Nautilus Oil and had replaced the plugs with the oem spec and still the BOG rears it ugly head occasionally on my own and always under load with a skier.

P.S. The engine still has the factory Oil Injector, this will be removed this season.

Any thoughts would be appreciated!

 

[flyingscott]

Have you done a compression and spark test? Have you tried pumping the primer ball when that is happening? Have you checked to make sure all the linkages are moving smoothly? Is the motor running hot? When was the last water pump service done? When was the lube replaced in the lower unit? Are the fuel lines in good shape? Fuel system clean?.

 

[Chris1956]

I have the same motor on my 16 footer. I run a 21 or 23P prop, however, my boat is probably lighter than yours. I therefore suspect that you are slightly over propped. A 19 P prop would probably fix your issue.

Any idea the max RPM you can get out of her, with max trim?

 

[Faztbullet]

You don't need to change props, you need to change the accelerator pumps on carbs....

 

[QBhoy]

Faztbullet above has the answer ! Or at least something along the carb lines. 99%

 

[QBhoy]

I was tinkering with a wee yamaha 3hp Malta I got cheap years ago. Wasn’t running, so I had the carb off it cleaning.
An old fella started chatting to me whilst I was doing this. Told me he had problems with a 90hp merc on his boat during the season. He gave me a great tip. One I’ve never heard before. Likely many of you have though.
His 90 had 3 cylinders and 3 carbs. He suspected one of them was at fault and causing bogging down. He got a piece of card paper folded over so he was able to hold it over the inlet to the carb...basically manually choking it whilst listening to the engine note.
Superb we top tip for carb trouble shooting. Fair play

 

[Dukedog]

this....

You don't need to change props, you need to change the accelerator pumps on carbs....

or disconnect tha little linkage to make them inoperable.. I pulled all tha guts out and epoxied tha pump bodies ona 245 that had 'em way back when to cure basically same problem...........

 

[jimmbo]

You don't need to change props, you need to change the accelerator pumps on carbs....

Accelerator Pumps? When did Mercury put Accelerator Pumps on the carbs for these engines?

 

[Faztbullet]

Several V-6 models have em...started in the 90's

 

[Dukedog]

'91, first year of wmh's (all of 'em)... pump guts went away but castin' stayed in '92/'93 then castin' went away.. didn't work out like they thought they would........

 

[BrettNC]

Could be accelerator pumps or general gas restriction. Rebuild carbs, check primer bulbs, check antisiphon valve at tank, check fuel pump.