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Noel Schembri
Noel Schembri, Marine Technician
Category: Boat
Satisfied Customers: 1951
Experience:  Advanced technical diploma
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I have an 80hp Mercury Outbaord oil injection 1987. Some

Customer Question

Hello, I have an 80hp Mercury Outbaord oil injection 1987. Some months ago the seal between the cylinders went so it wasn't burning all the fuel and the boat was going very slow with unburnt fuel coming out of the exhaust. We put a new seal ring in and fixed the problem. However the boat is now running slow again but not as slow as before. Its gone from a top speed of 40 km/hr to 30km/hr. I can also see fuel rising to the surface of the water. So my question is do I have the same problem again and if so what is causing it?Thanks,Daniel
Submitted: 1 year ago.
Category: Boat
Expert:  Noel Schembri replied 1 year ago.

Hi Daniel my name is ***** ***** I will assist you. the problem you are describing could also be coming from a fouled spark plugs or a dirty carb. So what i first suggest you do is to remove the plugs and check the burn. It should have a brownish color. If it is too black then there is too much fuel going to that cylinder, whilst if it is white fuel is not going in or not being burnt. At this stage i would have the spark on each plug checked and if one of the is not a blue spark then try and change the spark plugs. If the spark is ok then next step is to remove the carbs and give them a good clean, especially if the engine has not been used for a while. Finally if the problem persists, you would need to check also the fuel pump which may have started to crack thus allowing too much fuel into the engine.

Check the above and let me know.


Expert:  Noel Schembri replied 1 year ago.

Hi did you manage to solve the problem? Do you require further assistance?


Customer: replied 1 year ago.
Hi, yes I just had a look and the top spark plug was very oily with black oil on the threads the other 2 plugs looked normal and dry. Also a while ago I was messing with the check valve on the fuel pump. I thought it was a valve for fuel and was trying to open it up to let more fluid through. Do you think I could be letting too much oil in this way or could it be something else?Thanks
Expert:  Noel Schembri replied 1 year ago.

Hi again, ok at this stage i would first try a set of spark plugs and see how it goes as the top may be fouled. If it still persists then rebuild the pump.