1987 Mercury 115hp 6cyl Tower of Power bogging down

wmedernach

Recruit
Joined
Aug 28, 2017
Messages
1
I've read many posts on here regarding bogging down on these mercs, and I'm trying to troubleshoot my specific scenario before I take it into a shop.

This motor started and ran great for an afternoon of tubing and skiing. Later in the afternoon while tubing, we made a sharp turn and the motor must have been trimmed a little high, and the engine kind of 'cavitated' as we made the sharp turn, and I pulled the throttle back. From that point on, it seemed to idle a little rougher but nothing major, and anytime you try to put the throttle down (gently or fast) it just bogs down.

We changed the spark plugs, and the fuel filter was full of black particles which indicated the fuel lines are deteriorating, so it was replaced. This did not fix the problem. I have since checked the spark on each cylinder, and that seems fine. The compression on all of the cylinders is in the 90 range.

I've read in the forums that the carbs could be glogged and need to be cleaned or rebuilt, or the stator could be shot, amoungst other potential issues.

Due to how this problem began, with the engine cavitating, I'm just questioning that it's the carbs?
Anyone have some suggestions on what I should be checking next?

Thanks in advance...
Warren M
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Just how high was the engine trimmed. The trim system on your engine is capable of trimming very high, too high in fact for many boats and that can lead to water starvation of the water pump.

Try spraying a gas-oil mix into each of the carbs, it it runs poorer, that carb is probably fine, if the engine picks up, then that carb is suspect
 
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