Idoling issues

[broken talon]

My Johnson 50 cranks and runs at idol while hooked to a water hose but will not when in the water. Once it's running it will run at higher rpm's great but dies when you cut it back to close to idol. Why?

[Rebel Sympathy]

We have a limited amount of information to work with. What year is your 50? When it idles does it "spit" and die or just stay smooth and die?

[broken talon]

It is a 2000 50HP. When it idols with the hose on it, it runs perfect. When it's in the water it will not idol at all. The only way to get it to run is to catch it turning over and give it throttle to get it going quickly. Then it will run fine until you cut it back close to idol again and it dies.

[Rebel Sympathy]

I asked the year of your engine because your it's symptoms remind me of an issue we had years ago. There was an OMC technical service bulletin about it; it involved drilling an extra drain hole inside the midsection or gearcase to prevent water from backing up the inner-exhaust housing and shutting down the engine at idle. I believe it was either the 2-cylinder looper (like yours) or the 3-cylinder looper.

Your motor runs fine on a hose but not when the gear case is submerged. I would venture a guess that it either has an issue with exhaust back pressure or water backing up the inner exhaust and smothering the engine at idle. The technical service bulletin pertained to motors much earlier than yours, so drilling a hole is probably not the answer. HOWEVER, you may have some kind of drainage or exhaust partial blockage in your midsection or in the exhaust passage of the gearcase. Perhaps someone had the gearcase off to change a water pump and the inner exhaust seal fell out of place. Regardless, I believe you are going to have to drop the gearcase and see if anything is mislocated or if some foreign object, such as a shop rag is inside the mid-section or inside the exhaust passage.

The only other thing that comes to mind is that outboards do not run quite the same on a hose as they do in the water. The difference has to do with lack of exhaust back pressure on a hose. So, if the carburetor is off adjustment just a tad, that can affect idle quality in the water but not on a hose. That is why the older service manuals always cautioned to make final carburetor adjustments in the water - not on a hose. I'd check that first, since adjusting a carb is much easier than dropping the gear case. Let us know what you find.