96 Merc 9.9 revs out in reverse, but not forward??

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Redthies

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I just bought this motor, and as the title states, it only revs to about half throttle in forward, but seems to rev out all the way in reverse. It starts first pull from cold, and idles great too. I'm thinking it must be some sort of linkage issue, but I adjusted the throttle stops and idle screw etc with no luck. I've got it on a bare 1436 Jon and with myself (175 lbs), and a friend (150 lbs), 2gallons of fuel and two tall cans and it won't even plane. It's like a 4 hp. Any thoughts or ideas what I should look at next?

Thanks!
 
I spent some time on the phone with a couple of Merc dealer techs, and got a few responses. Base gasket turned to mush, exhaust carbon build up/tarring, carb clogged, coil cracked/broken and on and on.
Some times it's really simple though. I figured I'd change the plugs and test spark, and while doing that I went back and forth a few times from cylinder to cylinder and noticed one with lower spark. Tried swapping plug wires from one to the other and while doing that I felt a "soft" spot in the longer plug wire. Cut the wire at the soft spot and there it wasn't! The plug wire had completely corroded through at that spot. I pulled the coil end crimp off, moved it to good side of the wire, plugged it back in and next thing I know I'm doing 20 mph +/-!
I figured I'd post up the solution here as when I was researching this, 90% or more of the threads I read the OP never posted what his outcome was. It's hard enough to diagnose things over the web, but even harder when you read a bunch of problems but don't see any results. I wouldn't have thought my engine was only running on one cylinder because it started so easily and ran so smoothly! Hope this helps somebody else.
 
Excellent self-diagnosis and lessons for all ... i.e., operation in reverse may not confirm that all is 'otherwise OK' in forward.

Kuddos for you in coming back and providing the answer too, good job! Plus also helps preserve the integrity of the archives.
 
Thanks! I fought the hard-starting, poor idling for years on a Johnson 4. I finally did a test. Pulling one wire killed the engine, whilethe other made no difference. The problem didnot follow the plug or the HTwire. One coil was cracked.
 
DaleH said:
Excellent self-diagnosis and lessons for all ... i.e., operation in reverse may not confirm that all is 'otherwise OK' in forward.

Kuddos for you in coming back and providing the answer too, good job! Plus also helps preserve the integrity of the archives.
Yes indeed, a lot of people will not take the time to post the fix for their problem once it's identified. That just leaves the rest of us wondering what the fix is when we run across the thread. I'm glad you were able to identify it yourself and save yourself the expense of taking it to a shop but and thank you for posting the solution to your problem.
 

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