Help me figure this out.. please!

I have a 1994 25hp Merc 2stroke. In freshwater, it runs like a champ. All season, duck hunting and fishing, no issues in my local lakes, river, creeks. But when I take it over to saltwater (Mosquito Lagoon/Indian River) it won't develop power. Like its on one cylinder. Only there. And every time I've tried it in the past couple years (only about 4, since I realized this was a chronic thing). This post Sunday I tried again...same result. Pulled it out of the salt, drove an hour, plopped it in the St. John's River and it ran like a sprayed roach. Any ideas at all? Driving me nuts.

Saltwater is much more conductive for electricity than fresh water, I'd start searching the electrical portion of the ign system.

I was thinking about that. But how does the salt water affect the ignition system? I'd think it was pretty well separated from all that stuff.

I had posted the problem before, but I wasn't sure at the time of the salt vs. freshwater correlation.

https://www.tinboats.net/forum/viewtopic.php?f=4&t=31855

But, now I am. But how would the fact that salt water is around the foot of the motor, and in the cooling system, have any impact on the electrical system up top? Not doubting it, but trying to learn... it's hard to pick this stuff up on your own!

You may have a VERY slight leak from the head or some of the cooling water getting up around some of your electrics. When you are in fresh water, no issue. But when you are in salt water, the extra dissolved salts and minerals cause the water to conduct electricity more quickly.

Contrary to popular belief, pure distilled water does not conduct electricity very well. It is all of the dissolved minerals and salts (even in normal tap water) that causes it to conduct electricity. Salt water has a far higher concentration of dissolved salts which are negative ions floating around in the water. Those negative ions are very conductive and reactive. These dissolved ions are also the reason that salt water corrodes metals far faster than fresh water does.

I would look for any small leaks or other ways that the salt water is getting close to your electrical system, particularly your coil and plug wires. Open up all connectors and look for signs of corrosion. Check all of your wires for worn spots on the shielding. Make sure that you aren't getting any splashed water up inside the motor cover during launch or use. Any amount of water getting in there could cause issues.

If it is as consistent as you say, it should be fairly easy to find.

Good luck!

[url=https://www.tinboats.net/forum/viewtopic.php?p=351538#p351538 said:

MRichardson » 36 minutes ago[/url]"]I had posted the problem before, but I wasn't sure at the time of the salt vs. freshwater correlation.

https://www.tinboats.net/forum/viewtopic.php?f=4&t=31855

But, now I am. But how would the fact that salt water is around the foot of the motor, and in the cooling system, have any impact on the electrical system up top? Not doubting it, but trying to learn... it's hard to pick this stuff up on your own!

Click to expand...

My "guess" at what the problem is, is nothing more than a "guess" based on the information given. You say it runs fine until you try to run it in salt vs fresh water and that the type water is the only thing that changes from having a good runner to having issues. The only connection that I can think of that might be attributed to this change would be that the saltwater is some how affecting the ignition system because of it's higher conductivity properties. If it were me, I'd probably give the ign wiring a good visual inspection for rust/corrosion, lose connections, etc and then put some muffs on it or put it in a test barrel and run the motor while looking for any water leaks in the cooling system up top that could affect ign wiring.

Makes sense, will do this this weekend.

As for other possible causes to inspect... idling long way out of idle zone/shallow water.
Hey, a 1994 2-stroke 25hp tiller doesn't have anything like a "safe" mode does it?
For overheating due to.. I dunno, higher-density water? (I know, maybe a stretch there) or longer time at idle and the cooling system is working better at high speed than low speed.

It was a leaky tell take house. Thanks JMichael!