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Mercury 9.8 Switch box Problem?

jcubb

New member
I have a Merc 9.8 that is running pretty poorly. The engine will fire up but it seems to be misfiring on one cylinder sporadically. When I pull the plugs one is significantly more fuel covered than the other. The running speed also seemed to be much higher on the second time I ran the engine. I had the carb and fuel pump assembly apart and it seems to be in order. The only thing that I can think of is the CDI box as I know that these are a common failure point.

Does anyone think this sounds like a problem with the CDI box? what are the symptoms of a CDI box going bad?

I am also wondering if these boxes are fairly interchangeable from year to year and from 7.5 to 9.8 engines. I do have a couple spares but one is on a 7.5 and I have no idea if they are any good either.

Any help is appreciated.

Thanks
 
The 7.5 and 9.8 are essentially the exact same for a given year.----The 9.8 has slightly bigger intake transfer ports in the side of the block.
 
I did solve the switch box for those who may be browsing in the future looking for the same answer. I was able to use the 339-5287 in place of a 339-6222a. The only difference that I found was the ignition coils were switched? it took me a while to figure out but for some reason when I switched the box I also ended up having to switch the plug wire position to the other ignition coil.

I can't say for certain if the engine was running like garbage because of the switch box though as I also replaced the Trigger coil that is under the stator at the same time.

Lucky for me, now there is a horrid knocking sound. I'm fairly certain I have a rod bearing out of the engine. I used a stethoscope and did not hear the knocking sound when placing the end on the engine block at the top or at the bottom. The knock was clear as day on the recoil though.

I was able to start the engine without the recoil on but it was still making the sound. After this I could apply the stethoscope under the flywheel and i can hear the knocking sound again.

Does anyone have an idea of what to look for at this point before I rip apart the engine and replace the block I have 3 engine blocks in my garage and they all seem to have similar play when rotating the flywheel back and forth by hand. I just don't want to go through all of the hassle to find out that the other 2 blocks I have are junk also
 
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