115 Mercury loses power in water

Ok where to begin..I have a 115 Mercury inline 6 that runs perfect..Out of water that is. When its in the water it starts up and idles perfectly, but when put in gear it bogs down under pressure and runs like crap and the RPM's do not pass 2000. The motor runs better in water in reverse then it does foward. Any ideas?

Re: 115 Mercury loses power in water

First run a compression check and give us a update on the numbers. When was the last tune up?<br />Just a guess fuel supply may be in play here also we will need more information on year model etc.<br />Thanks, Tim

Re: 115 Mercury loses power in water

Fischer18, That is the classic example of a carb problem. Specifically, either the carb idle mixture screws are not set correctly, or the carb idle passages are dirty. If you haven't messed with the mixture screws, and the motor used to rev up correctly, you likely have dirty carbs. If you have adjusted the idle mixture screws recently, you have misadjusted them, and the mixture is too lean. The correct setting is to make the idle mixture as rich as possible, while still having a reasonable idle.

Re: 115 Mercury loses power in water

Also.. this is a classic example of being overpropped. What's the boat specs and what's the prop pitch?

Re: 115 Mercury loses power in water

Heres some more background on it...Like I said it runs absolutely perfect out of water. But when in water and under pressure doesnt want to move. I replaced the fuel tank and fuel lines..Still didnt fix the problem..Then someone told me one of the switch boxes was bad..so I replaced the one that I thought was broken it ran a little bit better. I should have just bought both and replaced both at the same time now I know next time if theres two of somethin better off repacing both...the boat would cruise at 20 mph hour then every once and while the tower of power would wake up and more then double its speed reaching around 40-45 but then shortly after would bog down again..Im goin to replace the other switch box as well. The wires from the switch box and coils were kind of getting mushy and the wire was losing its integrity so I spent one ENTIRE day replacing every wire one by one. Then I replaced the fuel pump diaphram. Problem still exists...The mechanics I talk to think that its either the spark advance module..which I already have just didnt replace it yet or another mercury mechanic believes that the stator has gone bad and had recommended replacing that..I think Im goin to start with the advance spark module and the stator...hopefully something will come of that...As for the year of it I know the motor is in between 82-89..Not sure exactly what year or how to find that out..the serial number is 600133..thanks for your help

Re: 115 Mercury loses power in water

You should really check compression. I just had the exact smae problems with a 70 hp mercury that you a having now. I thought it was ll the same things and wasted alot of money rebuilding carbs and rplace stator, switch box, plugs and lots of adjusting time. It never would run right so I finally took it to a mechanic and I had no compression from no. 1 cylinder. Turns out that it had been burned up. I was told that if I keep running it that it could possibly start breaking up and sling a rod and that would completely riun the engine. So definiately do a compression check.

Re: 115 Mercury loses power in water

Ok thanks I will do a compression test...So what did you have to do to fix that?

Re: 115 Mercury loses power in water

had that problem with 2 of them a little older then yours ,but i thought i got this great .. i know tons about cars they ran great on land with muffs i mean great..bad compression.. i also had a 135 johnny same thing rebuit power head myself...not again