Advice needed on a 1984 Mercury 7.5 hp

[Marc417]

My motor won't run on both cylinders unless the coil wires are reversed. The bottom cylinder is working fine but the top cylinder will not run. Its getting spark to both cylinders. The guy working on it is a little stumped as to why. With the coil wires reversed it runs and idles fine but won't pump water. With the wires in correct order it pumps water fine but only the lower cylinder is working. Any help or ideas is appreciated. Thanks.

 

[racerone]

Which coil wires ??-----With plug leads reversed it will / should not run at all.-----Has the mechanic checked compression ?----Checked reed valves ? ---Has he installed a new impeller ?

 

[Marc417]

From the mechanic:

Yeah, I checked compression, new impeller, reeds are good and fire is great on both Cyl. They are right, it should not run with the plug wires switched, that's what's so baffling. It's got to be something to do with the stator or that flywheel.. If somebody can explain why the motor runs better backwards than fwd I'm all ears lol. There is no timing adjustment that I am aware of to fix it.

 

[racerone]

Maybe the flywheel key is sheared ?

 

[quicktach]

Get a wiring diagram and carefully check the wiring to see if there's a wiring error/cross.

 

[Marc417]

He sa8d the flywheel kets look great. Thanks. I will try to find a wiring diagram

 

[Marc417]

He said the flywheel keys look great. Thanks. I will try to find a wiring diagra

 

[Marc417]

He's suggesting that I buy a new switch box. Says he's pretty sure that will fix it. Any thoughts on if it sounds like a switch box problem

 

[racerone]

You said it has great spark !--------why would a new switch box work better?

 

[schematic]

been bit on this before.....wrong coils or failed box can do this. If you check with a timing lite you may see both plugs are firing at the same time which will make only one cylinder happy.