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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 a 1987 mercury 200. Boat was running fine the

Customer Question

I have a 1987 mercury 200. Boat was running fine the suddenly won't go over 2-3k rpm under a load. I have checked resistance on stator and trigger both are in spec. I have replaced plugs ( ngk BU8H) all 6 are getting good fire. After that I checked the fuel system. All checked out good. Moved on to carbs. The bottom carb had fuel on top of it so I took themy off and cleaned and rebuilt them. After all this the boat still won't go over what seems like half power. If I let of the throttle from full it jerks like it wants to go but doesnt. I'm at a wall right now of what to check now. Also has new switch boxes and fuel pump rebuilt.
Submitted: 12 months ago.
Category: Boat
Customer: replied 12 months ago.
It also idles fine. At time it will hit and go to plane and run fine. But this is maybe 10% of the time. It is propped correctly and has ran fine with its current set up
Expert:  Noel Schembri replied 12 months ago.

Hello my name is ***** ***** I will assist you. The problem you are describing seems to be linked to fuel starvation. Best thing to start with is to try the boat using a separate fuel tank and line and see if it makes any difference. If it does then the problem is due to a blocked / clocked fuel line. Check the above and let me know.


Customer: replied 12 months ago.
Fuel system is clear
Expert:  Noel Schembri replied 12 months ago.

Ok next thing to do here is to check for spark on all spark plugs, see if there is a side of the engine (3cylinders) without spark and let me know. If there is spark check the fuel lines from the priming pump to the carbs. Make sure the pump sucks fuel from the bowl and delivers to the top of the carbs as otherwise it will flood one particular carb reducing power.


Customer: replied 12 months ago.
Has good spark
Expert:  Noel Schembri replied 12 months ago.

Ok , had a similar issue with one of my clients which ended up being a defective wire going to the switch box. I suggest you check all the wiring that have good continuity from one end to the other. Also if possible when the problem occurs check for spark then as it may be cutting out on some cylinders.


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