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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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Jeff I have a Mercury 6cyl 90hp 1978 which starts well ,ticks over well will run on hal

Customer Question

Hi Jeff I have a Mercury 6cyl 90hp 1978 which starts well ,ticks over well will run on half throttle fine but when more than half throttle is applied it seems to bog if I leave morse in flat out position it will stall out completely if when it begins to bog it is reduced to idle it will keep running any ideas ?? Many thanks
Submitted: 2 years ago.
Category: Boat
Expert:  Jeff G. replied 2 years ago.
Steve is this a recent problem or something that has been going on?Can you do a few tests?I would like you to do a compression test and check for good spark on all 6 cylinders. You can borrow a compression tester from most auto parts stores and a spark tester is about $15. Great toolbox tool.With the engine off look past the front cowl support into the carbs. Have a helper slowly open the throttle all the way. Do the throttle plates open all the way parallel with the throat of the carbs? Check all 3.If on the float bowls of your carbs is there a cylinder looking cap held with one screw or is it short and rounded? If the cylinder take that one screw out and check the filter screen underneath for debris or trash.Check these things and post back your results, we'll go from there.