Mercruiser 7.4 Loss 1000 RPM

[motowells]

I have a Bayliner 2858 with a Bravo II and Mercruiser 7.4L.

I recently changed the exhaust manifold and in doing so I changed the spark plugs and wires. When I tried to get her on plane it would only do 3600 RPM's at best. Keep in mind the boat sat in dock for 2 months in the summer without moving.

A marine mechanic said it was fouling. I had the boat removed and pressure washed and cleaned up, it was nasty; and by god it got her on plane. Unfortunately I still don?t have anywhere near the performance that it once had.

The prop was pitted on the ends but nothing major that would cause a 1000-1100 loss of RPM or would it?

Also my fuel consumption is through the roof. I was out for one hour at around 3300 and sucked about 13 gallons!

After bringing her back I could smell gas. Once in idle state the gas smell was gone. Leaky secondary pump diaphram?

I bought this boat back in March of 2007: It ran 4600 @ 28 knots. Cruising speed was about 3500 RPM @ 20 knots. I only used about a 1/6 tank at nearly 22 knots for 1.25 hours.

Tonight I am going to change out Cap and rotor but something tells me it might be a carb issue.

Any ideas?

Thanks in advance,

Jeff
Port Orchard, WA

 

[Bondo]

Re: Mercruiser 7.4 Loss 1000 RPM

After bringing her back I could smell gas.
but something tells me it might be a carb issue.

Ayuh,.......... I Gotta Agree.............

 

[180shabah]

Re: Mercruiser 7.4 Loss 1000 RPM

Excessive fuel usage and the smell of gas.....Rebuild the carb.

 

[MikDee]

Re: Mercruiser 7.4 Loss 1000 RPM

Recheck your spark plug wires to make sure you put them back on the right plugs!, being as you changed out the manifold, a crossed plug wire could do this, including the excess gas smell, from unburned gas due to this.

 

[Redneck Yacht Club]

Re: Mercruiser 7.4 Loss 1000 RPM

Compression check, First! Saltwater motor? And the fuel, is a winter blend? Need more info.......

 

[motowells]

Re: Mercruiser 7.4 Loss 1000 RPM

This is a fresh water cooled motor.

All mostly new gas in tank. I have changed the fuel filter and no signs of water.

I took the distributor cap off last night and noticed that there was a bit of corrosion. I cleaned it up a bit and noticed I was able to get a wee bit more top end maybe 100 to 200 RPM's. Still no where near where it should be; but could this be an indication that its ignition issue?

By the way no smell of gas last night when buzzing around. (I know hold the jokes)

Could a coil cause all this? I noticed yesterday as I was poking around that it appeared old.

Thanks for all your replys!

Respectfully,

Jeff
Port Orchard, WA

 

[searay3]

Re: Mercruiser 7.4 Loss 1000 RPM

There is also the clear line that goes to the carb from the pump. If the diaphragm busted its pumping excess fuel into the carb instead of the bilge. If you have an electric pump this does not apply.

 

[motowells]

Re: Mercruiser 7.4 Loss 1000 RPM

I finally found the reason for the loss of RPM. The tech that put the wires on crossed two and that is why it was not "firing on all cylinders". So I took it out this weekend and sure enough it was back to its good ol self.

Thanks for all your advice and suggestions!

Respectfully,

Jeff
Port Orchard, WA

 

[Haut Medoc]

Re: Mercruiser 7.4 Loss 1000 RPM

That will do it....
Maybe I'll see ya out there, but not today......​

 

[MikDee]

Re: Mercruiser 7.4 Loss 1000 RPM

I finally found the reason for the loss of RPM. The tech that put the wires on crossed two and that is why it was not "firing on all cylinders". So I took it out this weekend and sure enough it was back to its good ol self.

Thanks for all your advice and suggestions!

Respectfully,

Jeff
Port Orchard, WA

I told ya so! But, you wouldn't listen, How do you think I knew, don't ask,,,
Very glad you got it fixed and back to normal, without too much wrong.