1974 mercury 1150 good spark but cylinders not firing

[DylRod94]

I had trouble with engine dying whenever I put it into water.
I was getting good spark on all plugs and what seemed like a good idle so I figured it was firing all cylinders well I went to pull the plug wires while running and it looks like cylinders 3,5,and 6 are the only ones firing. I assume its a timing issue since I have spark. Heres a link to me pulling the plug wires and one for just idle in water. Yes, on that last plug on the video it shocked the sh*t out of me https://www.youtube.com/watch?v=S1tvlbOOWtY https://www.youtube.com/watch?v=hbRgRnV5I58

 

[Chris1956]

That ,motor should have distributor ignition. As such, it has spark on all or no cylinders, unless the spark plug wires are bad. Check the spark plug wires for arcing to ground.


Put a timing light on each wire to confirm spark to each cylinder. After you confirm spark to all cylinders, suspect water infiltration to the cylinders that do not fire. Usually an inspection of the spark plug's color will indicate water infiltration.

 

[opalized1]

now just to throw in my 2 cents, I was working with a 950ss thunderbolt engine someone gave me, fired, and ran on idle and just off idle all day long, but had no mid range or top end, I went through everything trigger, control box, spark plug wires, sparks plugs, etc. ok so in the end, compression was equal within one lbs on all cylinders, but when I pulled # 2 or # 3 spark plug wires off running, there was no change in rpm, if I swapped 2 to 3, I would get an increase in rpm of 60 or so, and # 4 and # 5 caused a drop in rpm of only 60 rpm, while # 1 and # 6 would drop rpm by as much as 120 rpm. Bottom line, someone had replaced the cap and wires I am guessing with ebay used, and never checked firing order, the cap was wired totally wrong for my motor, and it ran, started great, and would idle or troll on plate all day long no issues, not one single wire was correct in the cap, so check firing order, ya just never know

 

[DylRod94]

now just to throw in my 2 cents, I was working with a 950ss thunderbolt engine someone gave me, fired, and ran on idle and just off idle all day long, but had no mid range or top end, I went through everything trigger, control box, spark plug wires, sparks plugs, etc. ok so in the end, compression was equal within one lbs on all cylinders, but when I pulled # 2 or # 3 spark plug wires off running, there was no change in rpm, if I swapped 2 to 3, I would get an increase in rpm of 60 or so, and # 4 and # 5 caused a drop in rpm of only 60 rpm, while # 1 and # 6 would drop rpm by as much as 120 rpm. Bottom line, someone had replaced the cap and wires I am guessing with ebay used, and never checked firing order, the cap was wired totally wrong for my motor, and it ran, started great, and would idle or troll on plate all day long no issues, not one single wire was correct in the cap, so check firing order, ya just never know

That was the problem got it running good and flipped it for a profit