1978 Johnson 85ETLR78C 85hp Outboard Motor - Fuel Leaking from Air Box Drain Hose

1978 Johnson 85ETLR78C 85hp Outboard Motor - Fuel Leaking from Air Box Drain Hose

I need some help figuring out why I have fuel leaking from my air box drain hose into the air box from the crank case. It only leaks when the motor is in the higher rpm range from 3000-5000. It does not leak at idle or even when its below 3000 rpm. The motor currently runs perfect, starts right away, idles fine and runs wide open great. So why is the fuel coming into the air box? I recently replaced the air box gasket, but there is just to much fuel to keep it from leaking down and into the water. I have done no other repairs since it started leaking except take off the upper carb to reattach the fuel line that was leaking at that carb. I have ran the boat with the air box cover off and it doesn't appear excess fuel is coming from the carbs so I doubt the floats are to high but I could be wrong. I talked to a boat mechanic and he has never seen fuel come out of the air box drain and frankly it did make sense to him why it would run perfect if the crank case is being flooded with fuel?

Any help or help to get me in the right direction would be appreciated.

Thanks

Had a feeling this might be an issue no one is familiar with...........

Reel Magic said:

Had a feeling this might be an issue no one is familiar with...........

Click to expand...

Steady on there Mate.

Where was the motor made as there are a number of different oil recirc hose plumbing options?

You say that the oil is coming FROM the hose INTO the airbox yes?

Check your recirc line routing and check, possibly, the cleanliness and adjustment of the oil drain valve which is essential. Adjust to 0.040" after you clean it.

A thought for you to ponder......................

Your engine may or may not have this fitted depending on where it was manufactured.

Provide some pictures.

collector_inspector said:

Steady on there Mate.

Where was the motor made as there are a number of different oil recirc hose plumbing options?

You say that the oil is coming FROM the hose INTO the airbox yes?

Check your recirc line routing and check, possibly, the cleanliness and adjustment of the oil drain valve which is essential. Adjust to 0.040" after you clean it.

A thought for you to ponder......................

Your engine may or may not have this fitted depending on where it was manufactured.

Provide some pictures.

Click to expand...

I will get a picture up later today when I can get down to the dock. Being that this is a 2 stroke with 50:1 gas/oil mix I am assuming we are using fuel/gas/oil as interchangeable terms.

Yes fuel/oil is coming from the crankcase through the airbox drain hose into the airbox. This is only happening when the engine is running under a load at 3000-5000rpms. It does not leak when idle or at any speed under 3000rpm.

Oil drain valve? I am not familiar with this part seeing this is a 2 stroke could you explain further?

One though occurred to me, shouldn't there be negative pressure in the airbox drain hose seeing that it is suppose to suck any excess gas from the air box back into the crankcase? Why does it lack negative pressure?

The only other thing that might give a clue to the problem is that I replaced the zip tie that secures the fuel line to the upper carb because it was leaking and the problem seems to have appeared after that.

Thanks for the response, will try and get pics up today.

Here are a couple of pics:


This is a pic of the airbox with the cover taken off looking at the carbs. The leak is coming out of the small hole at the bottom right hand side of the lower carb.


Close up of the airbox drain hole


This is a pic looking from the top of the airbox and carbs. The leak is coming from the small black tube at the bottom.


I also noticed today that when I put tilt the motor up a large amount of fuel leaks out of the airbox drain hose so obviously the crank case is flooded. Despite all the extra fuel the motor runs great.

Have you checked the fuel pump diaphragm ?

racerone said:

Have you checked the fuel pump diaphragm ?

Click to expand...

What would I be looking for if it is the problem?

A hole in it.

Ok thanks that make perfect sense!!! I will check tomorrow. Thanks for all your help!

Well the fuel pump diaphragm was perfectly fine... I took off the carbs to check the floats, they were also adjusted properly. Pretty much have no idea what to do at this point. I decided to order a fuel line check valve to install in the air box drain hose since I am out of options. I will update if it works or not.

Installed the check valve in the drain hose, dropped the boat in the water and no more leak. Don't really like fixing things by not find the exact cause but it appears to have worked. Hopefully there is no long term issues with a so called "Mcgyver" fix.