Motor wont revup in the water with prop attached but will with prop removed.

[KevMiller]

1983 Mercury 50hp 4 cylinder

 

[KevMiller]

1983 Mercury 50hp 4 cylinder, it revs up in gear when on muffs but when I bring it to the lake it revs in neutral but put it in gear in will not rev up to full speed, it only goes about 5 mph, I removed the prop and backed it in the water at the landing and it revs high same as in neutral. Carberators have been disassembled and cleaned.

 

[racerone]

In gear with muffs is the same as NEUTRAL.------Stop running this motor.----Do some testing.------Post compression values.----Does spark jump a gap of 3/8" on all leads.----Sounds like it is running on 2 of 4 cylinders.

 

[KevMiller]

I will do compression tests again, how would I know if 2 of the cylinders aren't firing? brand new plugs recently and replaced rings on all cylinders.

 

[racerone]

Test spark first.-----All wires from switch box going to the correct coils.

 

[KevMiller]

Compression tests 8/3/2024

top 95
2nd 90
3rd 110
4th 100

good spark on all 4

Replaced spark plugs, stator, piston rings, switchbox, diaphrams and cleaned carbuerators in the recent past.

 

[KevMiller]

Test spark first.-----All wires from switch box going to the correct coils.

Not sure why but we had the top 2 spark plug wires crossed, never thought to move them until a couple nights ago, runs like a champ now, thanks for the helpful ideas.