Loss of power only around 3500 RPMs, pumping primer bulb relieves it

[tomfsu]

My 2001 Mercury 125hp motor starts losing power (slowly starts to drop rpms) after about 5 minutes of cruising around 3500 rpms . Once this starts to happen and I pump the primer bulb it quickly regains power and cruises at normal speed.

It cruises at WOT and almost any other rpm level with no problems, no hesitation. I replaced the in-line fuel filter and disconnected the fuel line and placed it directly into a portable tank. The engine is still having the same problems. Any help or ideas would be appreciated.


Thanks,

Tom

 

[Laddies]

Re: Loss of power only around 3500 RPMs, pumping primer bulb relieves it

Sounds like the fuel pump is going bad.

 

[CharlieB]

Re: Loss of power only around 3500 RPMs, pumping primer bulb relieves it

Or possibly a small air leak INTO the fuel line between the fuel supply and the fuel pump.

Check every connection in the hoses between those two.

Test by temporarily adding a section of clear hose between the fuel pump and carbs, watch for any 'air bubbles' which prove the presence of a leak.

 

[hkeiner]

Re: Loss of power only around 3500 RPMs, pumping primer bulb relieves it

The below Mercury advisory may help with checking the fuel supply system. If these tests do not indicate a problem with the fuel pump or fuel lines, I would next suspect gummed up carbs. The motor may be regaining power when you squeeze the fuel bulb because the increased pressure is overcoming a restriction in a gummed up passageway. I've seen that happen before.

As an alternative, instead of doing a lot of troubleshooting stuff, simply rebuild the fuel pump and clean the carbs and see what happens. There is a very good chance the problem will go away and these steps are periodic maintentance items anyway. I think that your portable tank test pretty much eliminated a possible problem with the fuel line upstream of the fuel pump.

Just my thoughts....

 

[tomfsu]

Re: Loss of power only around 3500 RPMs, pumping primer bulb relieves it

This is great information, thank you all for the insight. I will let you know what happens.

 

[j_martin]

Re: Loss of power only around 3500 RPMs, pumping primer bulb relieves it

Whatever you do, don't run it like that. It's a good way to burn a piston.

hope it helps
John