runs in the yard.....not in the lake

[suedee33]

We have a 1990 johnson proseries 50 hp engine. It runs when we hook the hose to it in the yard, when we put it in the lake it starts up and cuts off in seconds. any ideas about what is going on? this pontoon and motor were given to us, but as far as we know it had a pretty good life.

 

[SparkieBoat]

Re: runs in the yard.....not in the lake

man that is a real general description. Anyone that tells you what is wrong with your motor can only be wild guessing. Diagnosing an outboard motor is a process of elimination. Start with compression test then spark test with a spark gap tester set at 7/16. post results, then we can begin to guess at your problem.

 

[suedee33]

Re: runs in the yard.....not in the lake

ok, we'll start there.

 

[Silvertip]

Re: runs in the yard.....not in the lake

There are some real simple things to check first. If the boat has a tach, what is it idling at. Just like your car, if it idles to slow it dies. When were the carbs rebuilt last. How long has it been since it ran last. How old is the fuel. See where this goes??? When running on muffs in the year there is no back pressure on the exhaust. The minute you dunk the boat, that back pressure affects idle quality and the engine may die. Carb adjustments and engine tuning should always be done in the water.