Merc 40 EFI Bigfoot low RPM @WOT

[smithmatbaker]

2002 Mercury 40 EFI 4stroke 4cylinder bigfoot on a 22' pontoon-Godfrey/Sweetwater 2221EL. Bought as a package, with a 13 prop. Only turned about 3900 RPM's at WOT. Repitched to 11, only turns about 41-4200. Runs perfect, not sure if tach is maybe off? Dealer not concerned about it, but I am.

 

[rickdb1boat]

Re: Merc 40 EFI Bigfoot low RPM @WOT

I'd be concerned, too, considering your WOT should be between 5000-6000 RPM's. Could be the tach setting is set to the wrong "Pole" setting. That would throw off your RPM readings. There's no way if the motor is preforming well, that you are only turning 4100 RPM's with an 11" prop. I'm betting it's a Tach setting or just a bad tach. Should be set on 6 pole for proper reading. You might check this out yourself and see if it's on the correct setting.

 

[The Marine Doctor]

Re: Merc 40 EFI Bigfoot low RPM @WOT

Running an engine that low of RPM @ WOT is not a good thing.<br /><br />I would also suggest you do some more checking, Tach and also possibly a flatter blade prop something with less cup.<br /><br />TMD

 

[rickdb1boat]

Re: Merc 40 EFI Bigfoot low RPM @WOT

Even if you dropped down to a 9" pitch, that would only get you to about 4600 RPM's. What diameter prop do you have now? Do you know what speed you are running right now? Does the motor sound right? I would have to wonder about a dealer that would install a 13" pitch prop on a 22' toon with a 40 HP. I run a 70 HP johnson on a 20'er and use an 11" pitch. Huumm! Just checked the prop selector and you should be running a 12-1/2" X 8" pitch prop on your toon. Tell the dealer that!!<br /><br />This is a Michigan prop, but it is still a good representation of what you should be using no matter what brand is on there now. I would have (Make) him change it out!<br /><br />12-1/2 X 8" PN 031070 MICHIGAN MATCH CUPPED PROPELLER

 

[smithmatbaker]

Re: Merc 40 EFI Bigfoot low RPM @WOT

It does seem to run real good, speed is good, sounds great, fuel economy is good. Mercury suggests a 48-854342A33 Black Max, which is a 14X10. I currently have a 14x13, repitched to 11. I am leaning more towards the tach not being correct. Also, does anyone know the difference between the 40, 50 and 60 4 stroke EFI's? The power heads are the same part #. I see that the 60 does not have a restrictor plate in the throttle body, but assume that removing the plate from my 40 will cause the mixture to lean way out and melt my engine. Any thoughts? The ECM is a different part #.