98 150hp oceanrunner lean sneeze

[bassmaster59]

I recently purchased a 1998 Johnson ocean-runner 150 hp , model # J150execd. I noticed it had a lean sneeze when I first ran it. I went ahead and ran it 3 or 4 times after treating the fuel and checking everything. It always would have a sneeze when I first started it. Sometimes when I would troll it would sneeze, but very seldom. Usually after it warmed up it was ok. I replaced all manifold to block, and carb to manifold gaskets. As well as the fuel supply O-rings. I noticed the gasket between intake manifold and the block was not properly aligned when I tore it down from a previous replacement. I used a thin layer of grease to hold the gaskets in place and was extra careful to make sure everything was perfect while reassembling all the parts. It now has a lean sneeze for about 10 seconds when first started, then will never sneeze again that day. What could I have missed? I did not rebuild the carbs. The engine runs perfectly except the first 10 seconds. Ethanol is bad enough on our motors without running lean. I always add Star-Tron ethanol treatment to every tank of fuel. Any ideas? thanks, jeff

 

[joereeves]

I retired in 1991 so I'm not familiar with the design of your engine. However, that problem is a common one and when there are no gasket or seal problems (air leaks), the cause is normally a carburetor idle air bleed jet having a too large ID... too much air in comparison with the fuel being drawn in.... engine runs lean.

The jets have the size marked directly on them.

The cure is to replace the offending jet with one that has a ID a size or two smaller. Try one size at a time... you don't want to go too small and have the engine running rich at an idle.

You can find the offending carburetor by having the problem happening, then insert a couple fingers into the carburetor throat which will act as a manual choke and have the engine run a littler rich onthat cylinder. When the sneeze vanishes, you've found the problem carburetor.

 

[bassmaster59]

I retired in 1991 so I'm not familiar with the design of your engine. However, that problem is a common one and when there are no gasket or seal problems (air leaks), the cause is normally a carburetor idle air bleed jet having a too large ID... too much air in comparison with the fuel being drawn in.... engine runs lean.

The jets have the size marked directly on them.

The cure is to replace the offending jet with one that has a ID a size or two smaller. Try one size at a time... you don't want to go too small and have the engine running rich at an idle.

You can find the offending carburetor by having the problem happening, then insert a couple fingers into the carburetor throat which will act as a manual choke and have the engine run a littler rich onthat cylinder. When the sneeze vanishes, you've found the problem carburetor.

Thanks joe!