Low power and rpm at wot

[Chriswvlok]

I bought a Mercruiser MCM 4.3L Thunderbold 1998 serial number 0L069290.

The boat start easy and run even on idle and also sound great when it's WOT but it come slow out of the water and at WOT only get 3300rpm after a long time it did go up to 3800rpm. I open the oil cap when it running at 3300rpm and it looks like some milky drops spat out now and then. The oil on the dipstick looks clean no water. The cap have some condensation on it.

The compression on all the cylinders are between 170 to 180. I did not see water coming out of any spark plug hole when I test the compression.

The prop looks fine and are a 21P.

I do not want to start stripping unnecessarily and wast money and really would appreciate advise what steps to follow to narrow this problem down

Thanks

 

[Fun Times]

Re: Low power and rpm at wot

Hi there Chriswvlok, Welcome to iboats!

When you had the spark plugs out, what did they look like? Were they carbon fouled at all?

What is your engine temperature getting up to?

 

[ziggy]

Re: Low power and rpm at wot

this is a good place to start at.
2nd place to go to is the oem service manual. ya can see an online version here. look for the trouble shooting section if it's got one. confirm proper service manual by serial number.

 

[Chriswvlok]

Re: Low power and rpm at wot

Thanks for helping Fun Times

The temp run on or just over the 140 mark.

I add picks of the spark plugs this two is how they all look

 

[Chriswvlok]

Re: Low power and rpm at wot

Thanks Ziggy

I am going to start with that and run it down as best I can. The only thing what worry's me is the possible water in the oil.

I also order a manual from iboats and waiting for it.

 

[Haut Medoc]

Re: Low power and rpm at wot

Check through the list in the link Ziggy posted....
The plug on the right looks awfully clean, as in steam cleaned....
For the price of a couple of gaskets, I would pull the exhaust manifold & riser on the side with that shiny clean plug & look at the port....
As far as water in the the oil. drain it & see what it looks like....
If a leak is present, it may not be big enough to emulsify (milkshake)the oil yet, but you'll see water....

 

[Chriswvlok]

Re: Low power and rpm at wot

Thank you all for the great help. The previous owner show me record of service that say replace fuel filter so I assume it's good. But when I go down the check list provided I tear it apart to get it off and it was as dirty as can be. I think the boat place could not get it of and just leave it but still invoice him. After I replacement the filter the boat run great:laugh:

 

[Bondo]

Re: Low power and rpm at wot

Thank you all for the great help. The previous owner show me record of service that say replace fuel filter so I assume it's good. But when I go down the check list provided I tear it apart to get it off and it was as dirty as can be. I think the boat place could not get it of and just leave it but still invoice him. After I replacement the filter the boat run great:laugh:

Ayuh,.... Water in the fuel, don't happen on a schedule,...

with gas now-a-days, I carry a spare filter,...