64 Evinrude Sportwin 9.5hp firing on one cylinder

[soldierman79]

I just purchased the 64 Evinrude Sportwin and found it ran very rough. I discovered that while running I would pull the spark plug wire on cylinder one and it would die. Although when I would pull the number two plug wire it would continue to run. I pulled the plug and while still attached to the plug wire i saw it was sparking. Any suggestions would be appreciated. Thanks!

[tx1961whaler]

You'll probably find that if you use a spark tester (instead of the plug itself) it won't spark across much of a gap. A spark plug can show a weak spark in the air, but won't spark under compression.

The first things to do are to run a compression test (you can usually get a compression tester loaned from the auto parts store) and a spark test using a spark tester (5 bucks). It should jump a quarter inch gap with a nice blue spark. If the spark test is bad, then you'll have to pull the flywheel off. Most likely the coils are original, badly cracked, and need to be replaced.

[12fter]

i just ran into the same problem w/ my '75 johnson 6 hp, but mine did not run rough it is not uncommon for these motors to run smooth on one cyl in nuetral. it stumped me pretty good! this is what i did, i replaced the plugs, wires and boots ( you will probably need 6ft or more spark plug wire, depending on the size of your flywheel), points and condensers, and the upper crank shaft seal( you might as well replace the seal while your in there because you have to remove the armature plate to replace the wires) all these parts only ran me about $45 but before you do any of this check the compression under optimal conditions it should be @ 100psi per cyl, but no mater what it reads more importantly it should be even any differance more than 5psi between cyl 's means there could be something wrong in the combustion chamber( scored walls, sticking rings, cracked pistons ect) the coils last a long time, im not saying thats not the problem, but usually there the last thing to go bad, but like the pevious post said i would definitly do a visual check of them any cracking or burning, replace em. hope this helps you it helped me. late!!!!!!!!!!!!!!

[BSDenning]

I had a similar problem on my 1957 7.5 hp. The problem ended up being a blown head gasket. The blown head gasket was letting water into the cylinder and a drop of water would get in the gap of the spark plug and it wouldn't fire. It also had low compresssion in the cylinder where the gasket was blown.

I replaced the head gasket and now everything works great. Compression is about 89psi in each cylinder.

The first thing I'd do if I were you would be to check compression. This will tell you if you have a potential blown head gasket like I had.

Good Luck!