Engine surges at high RPM

[navy@zoominternet.net]

2005 Mercury 25HP engine surges at full throttle RPM drops from 4000 to 3000 or 3500. It surges back in forth between this range. It sounds like it is running out of fuel. At 3000 and below engine runs smooth and steady also the idle is ok and starts fine. Sounds like it maybe a fuel problem but not sure. any help would be appreciated.

 

[Texasmark]

What is the condition of your squeeze bulb when this surging happens? Run your rpms up to 3000 on the boat on plane on the water and after several minutes, grasp the squeeze bulb and feel how firm it is....should be soft but with fuel. Run your rpms on up to where it surges and feel the bulb again. What does it feel like?

 

[fhhuber]

Another 0 cost test... when it starts surging, unscrew the fuel cap a couple of turns. If the issue clears up your tank isn't venting properly.

 

[Texasmark]

Another 0 cost test... when it starts surging, unscrew the fuel cap a couple of turns. If the issue clears up your tank isn't venting properly.

If the bulb was collapsed that would be the place to go looking for the reason.

 

[jimmbo]

If full throttle is only getting 4000 rpm, you have a few things to check. Are you over propped? Dead cylinder?