mercury 115 hp 1991 loses power

[wazza]

still trying to find problem with motor losing power,had major service,new primer new petrol tank plus fitting,carbys cleaned,kit to fuel pump .motor will run fine at 2000revs 20mph and will trawl fine but if i go too hard it starves for fuel. checked with clear hose from fuel pump to carby and noticed air in line, could I be getting air sucking from between carby and motor. trying to find out if serice guy put new gaskets in or didnt take carbys off, but he hasnt got back to me yet. the service guy has no idea what the problem could be. already spent a bit $ with him but might have to cut my loses and go to someone else. cheers warren

 

[Texasmark]

Re: mercury 115 hp 1991 loses power

One would think that air in the line between the carb and pump have nothing to do with carb to intake manifold, or carb for that matter, gaskets. The fuel pump is sucking on the fuel line to the tank and there is a crack, bad fitting or something in that line, all the way back and into the tank till you get under fuel for that matter is all suspect.

If all else fails, install your clear tubing down (up) stream from where you are, in as many steps as you choose to, from under fuel level in the tank and see how far you have to go to get clear fuel. Then find the problem.

I think I'd disconnect the fuel line at the tank outlet and start there, then if clear, half way up, and so on, keep cutting the distance in half.

Fuel tanks usually have strainers on the fuel pickup and if you have had bad fuel, or used a water eliminating after market product, the problem could be in the tank; clogged strainer.

In hot weather, if you have an obstruction prior to the fuel pump it will create a small vacuum in the fuel line and that vacuum can cause fuel to boil, hence bubbles and is known as vapor lock. Engines can't run on bubbles.

HTH,

Mark

 

[CharlieB]

Re: mercury 115 hp 1991 loses power

Quick disconnect fuel fittings ohave a habit of O-ring seal failure, it seems to seal fine when you pressurize it using the primer bulb, yet the fuel pump pulls a vacuum and it sucks air in, reducing fuel flow, leaning out the upper carbs and melting pistons.

Many owners elect to eliminate the fitting altogether and run hose directly in, reducing the potential for a melt down.

 

[Texasmark]

Re: mercury 115 hp 1991 loses power

Many owners elect to eliminate the fitting altogether and run hose directly in, reducing the potential for a melt down.

That's the way my current engine was plumbed when I bought it used....still is. I didn't know why but this makes perfect sense. I never take the engine off the boat so what do I need a QD for?

Mark

 

[wazza]

Re: mercury 115 hp 1991 loses power

thanks mark.i was on my own and in windy conditions when i had the clear hose on so it was a bit difficult to clearly see what was happening but will keep checking cheers warren

 

[wazza]

Re: mercury 115 hp 1991 loses power

the first thing i did was to replace the fittings and then lines then tank but its not the first time someone got a bodgy fitting so will keep on trying. cheers warren

 

[BatDaddy1887]

Re: mercury 115 hp 1991 loses power

If you have a spare fuel tank/hose on your boat try that or borrow one if you don't, see if the problem still exists. Also, sometimes a simple thing like a prop change is the culprit. Perhaps bad gas in tank.....