Mercury 50hp power loss

[Steve6964]

I have a 1999 Mercury 50hp Bigfoot 4-stroke outboard(carborated). The motor is on a Myacht 35ft houseboat. While running the motor at WOT(3600rpms), the power dropped instantly to about half. Could only get about 2000rpms at WOT. Mercury mechanic checked the following and found no problems: ingnition timing, spark plug wires, replaced spark plugs, electronic ignition and checked compression. Also, I connected a fresh tank of gas to rule out the possibility of water in the gas. I also squeezed the primer bulb while under load & had no change in power. The engine idles and revs okay while in neutral, but when under a load it has no power and misses alot. The mechanic says there is no problem with the motor, but it's obvious there's something wrong. Any suggestions would be appreciated greatly!

 

[jim dozier]

Re: Mercury 50hp power loss

Sounds to me like you lost fire on 1 cylinder for some reason. I don't know what the mechanic did but since he didn't fix it I would start from scratch.<br /><br />Verify that you have strong blue spark on all cylinders. <br /><br />Check compression.<br /><br />Isolate which cylinder is not firing by removing plug wires one at a time and noting effects, then focus on that cylinder. Keep us posted.

 

[turtle1173]

Re: Mercury 50hp power loss

Hi,<br /><br /> The problem sounds "fuel related." Do you have a built in tank on the houseboat? Was this a different tank that you hooked up to it later? Does it miss a lot in gear at lower speeds also, or just above 2000 rpms?<br /><br /> This may sound odd because I don't know the details of your setup but make sure the vent on the tank is open if it is portable. I've experienced similar problems like that.<br /><br />Shane

 

[Steve6964]

Re: Mercury 50hp power loss

The mechanic verified the spark plug wires & plugs(new ones) are in good working order. The compression also checked good for all 4 cylinders. The boat does have a built in fuel tank. That's why & bought a new portable outboard tank, filled it with fresh gas & tried to correct the problem. With the vent on the tank open, the problem still exist. I can't get more than 2000rpms with the motor in gear. While at idle, the engine will rev up without a problem to 4000-5000rpms. Please keep the solutions coming. I appreciate ya'lls help.