1986 115hp leaks oil

[iceberg]

My 1986 Yamaha 115hp, when tilted, leaks oil through the carburetors, which eventually collects on the motor body near the front latch.It is a very slow leak. My understanding is that the oil is injected behind the carburetors into the intake manifold. Are there check valves to prevent this in this engine that are not working, or is it something else? I cannot find any sign of a leak elsewhere, and I have looked carefully several times.

[jb123]

there are check valves that can go bad and drain into carbs, and also....your oil tank overflow/vent drains into the airbox....check oil level when tilted AND check oil level at normal operation to see if your main tank is overfilling.

[iceberg]

I have the power off when I am not using the boat; I have checked for overfilling and it shuts off when the oil reaches the full mark.

[iceberg]

I should have added that there is oil on the choke plates and carb throats - some small drops as well as a general coating of oil in the inside parts of the carbs one can see -

[rwwillhunt]

I also have had a problem with one of my 1986 115 Yamaha leaking oil into the motor tank and over flowing making a mess by running off the motor. This happens when the boat sets up for any length of time. I think my problem results from the remote oil tank setting higher then the tank on the motor and siphoning into the motor tank. I have recently lowered it and so far the level on the motor tank has not increased. May be to early to tell but I think this has cured my problem.

[BQUICK]

Old thread but I recently had a cylinder that was misfiring intermittently. Coil power wire was not plugged into bullet connector...just touching. After fixing that I no longer get oil coming out carb throat when tilted up. I think since one cylinder misfiring the oil was not being drawn in and burned causing it to drain down and out the carb throat.

[yamaha1988]

It sounds like the oil is leaking from the oil injection system, likely due to an issue with the lines or seals. First, check the oil injection lines and connections for cracks or looseness, especially when the engine is tilted. Also, inspect the oil pump to ensure it's delivering the correct amount of oil—too much oil could cause leaks. Worn gaskets or seals around the carburetors or intake manifold may also be the culprit. Lastly, check the breather tubes for any blockages, as a clogged vent could cause pressure buildup and force oil out.

If you can’t find the source, a pressure test might be necessary.