15 horse force cylinder not firing

[sparks4540]

Hi folks. I bought a 15 horse force motor and it ran on both cylinders for about 30 minutes. Now it only runs on the top cylinder. I have replaced the reed plate gaskets, head gasket and fuel pump. The reed valves looked good and the worse case had a gap of .008 between the reed and the housing. According to the marine shop nearby, .010-.015 is an acceptable range. I have cleaned the carb and checked needle and seat. I cleaned and gapped the points and have great blue spark to both new plugs. I swapped the points,coils and condensers with no luck. Compression after five pulls is 110 top and 105 bottom. I hooked up a timing light and the plug appears to be firing when running. It will run for about 5 minutes on the top cylinder and then start to miss and I hear a snapping noise under the flywheel when it misses, like an electrical snap. Then I'll hear the snapping again, one after another and it quits running. There is no sign of arcing under the flywheel. The top plug is always dry and the bottom one wet. Any other ideas?? <br />Thanks.

 

[oldboat1]

Re: 15 horse force cylinder not firing

Be sure condenser wires are tucked down out of the way, and not in contact with the spinning flywheel. Besides checking to see that the magneto was reassembled according to the book, make sure the ground wire from the magneto plate to the powerhead is securely connected.

 

[scotiany]

Re: 15 horse force cylinder not firing

If your motor has a breather drain system, take it apart and clean it . I had breather drain problems on a 55. It's also called the puddle valve on older Chryslers.

 

[sparks4540]

Re: 15 horse force cylinder not firing

The only thing I see that catches my attention is that the top cylinder spark jumps about 3/8" to ground. The bottom cylinder only jumps maybe 1/16". Both sparks are blue, but there is noticable differences. All the wires under the flywheel are neatly tucked and tiewrapped into place. My guess is that I should probably replace the points and condensers anyway. Any thoughts?? I am not sure what or where the breather drain/puddle valve is or would be. Point me in the right direction and I'll check it out. I did have the head off and reed plate and the exhaust cover and the inside of the engine is clean with no carbon buildup. What do you guys think about the spark on the lower cylinder?? I have been told if it doesn't jump at least 1/4" to ground it's not good enough to fire the cylinder. It's the only thing that makes sense to me. I only have 2 weeks to play with this before fishing season..Serial no.1050 and model 152y9a. Thanks for you input.

 

[moderator1]

Re: 15 horse force cylinder not firing

^