1983 black max 150 running poor

[Mercury1150]

So I recently went and purchased a 1983 merc 150. Did what I thought was good enough check over before buying it, compression was good 120-125psi every hole it showed good blue spark on all 6 plugs. The previous owner said it started running bad one day so they took it to a shop and had stator and switch boxes replaced. They then took it out to the lake at it still ran bad. So the same shop said they needed to rebuild the fuel system, the cost of that was too high for him ( apparently the boat it was on was completely rotten) and that’s when I come into the picture. I took the engine home rebuilt all the carbs and the fuel pump hooked it up on my boat and it still runs poorly… verified spark with a timing light on all 6 but when I pull the spark plugs they all look wet and don’t appear to be firing well. Ohm tested the trigger, stator and coils, all six coils were low but the stator and trigger were perfectly in spec, this leads to my question. Is it possible that all six coils could go bad at once and still show good spark? Am I overthinking this?
Hopefully the attached video works, it runs ok on the muffs but will not plane the boat.
Any thoughts or previous experiences much appreciated !

 

[Chris1956]

A fuel pump diaphragm leak will allow raw fuel into the cylinders, causing hesitation upon acceleration, wet plugs, excess smoking.

 

[racerone]

Start motor.----Pull one plug wire off at a time.-----Note the response of the motor.-----Report the results here.

 

[Mercury1150]

I heard that can damage the switch box’s, dose doing it briefly not harm them that much

 

[Mercury1150]

And I’ll post a picture of the spark plugs

 

[Faztbullet]

I heard that can damage the switch box’s, dose doing it briefly not harm them that much

Old wifes tale

 

[Scott Danforth]

Use a non-metalic plug wire pliers when you pull the plug wires.

 

[markhodges78]

A fuel pump diaphragm leak will allow raw fuel into the cylinders, causing hesitation upon acceleration, wet plugs, excess smoking.

Seen this to many times .. raise engine up take the fuel line going to the carburetors off the pump and plug the pump then pump the bulb and see if fuel comes from the carburetors if it does then its a fuel pump issue...

 

[QBhoy]

Put a meter on the battery and make sure she’s charging.
Other than that. From personal experience with my own identical engine…have a look at the inline main fuse on the starboard side of the engine. I found mine was making an intermittent contact because of the fuse holder being a bit rubbish.
Other than that…check for any loss of continuity along the plug leads or their contacts. Even touch around the switch box and main circuits/ht leads and see if you get a shock off her..if you’re brave enough

 

[Mercury1150]

So my problem is fixed, When I did the spark check the lowest 2 cylinders seemed to make no difference. So I double checked the fuel pump as suggested and found I had a corner that was tucked in and was not sealing, she’s running great now!! 52mph with a 19” aluminum prop, definitely need a 21 stainless to lower the top end rpm and gain some speed, any suggestions for a good prop?

 

[v191Checkmate1969]

So my problem is fixed, When I did the spark check the lowest 2 cylinders seemed to make no difference. So I double checked the fuel pump as suggested and found I had a corner that was tucked in and was not sealing, she’s running great now!! 52mph with a 19” aluminum prop, definitely need a 21 stainless to lower the top end rpm and gain some speed, any suggestions for a good prop?

I'm glad it was such an easy fix. I wish that happened more for us outboard users