Won't rev up?

[waynerh]

Greetings all!
I have a 93 7.4 omc king cobra and had a problem yesterday. I took it out for the last horah and on the way back to the dock at about 3500 rpm's it stumbled hard and then wouldn't rev past 2k. It still idled smoothly but when I tried to give it more throttle, it would shake violently and not rev up.
I had just seafoamed it in my driveway a couple days previous (1/3 can down throat of carb, 1/3 in crankcase and 1/3 in tank). I wanted to put a load on it then bring it back and change the oil and oil filter.
I have a new fuel/water filter but I didn't have it with me(dummy). I was going to put it on when I finished changing the oil.

Any thoughts?

Thanks for your help and expertise!

Wayne

 

[Don S]

Re: Won't rev up?

The first thing I would check for would be water in the fuel.

 

[waynerh]

Re: Won't rev up?

Thanks Don S.

I will try that first. Would it still run well up to 2k with water in the fuel. I also neglected to mention that it ran fantastic for 2 hrs before the problem.

 

[Haut Medoc]

Re: Won't rev up?

Sometimes what happens is that the filter gets saturated with water & the extra demand (RPM) allows some water to get through......​

 

[waynerh]

Re: Won't rev up?

Hey Guys!
I replaced the water/fuel seperator and it solved the problem. It was completely full of water. I have only put about 40 hrs (2 months) on the boat since the tank was removed and drained and I live in Colorado where there is very little humidity. How could I have that much water in my fuel already?

Thanks!

 

[Don S]

Re: Won't rev up?

Leaky, damaged, or missing seal on the fill cap is one of the most common ways.
The vents location could also allow water to enter the tank.

 

[waynerh]

Re: Won't rev up?

I checked the seal when I draind the tank and it was and still is good as far as I can tell. I also replaced the breather and it sits about 2 feet above the water line.
I'm still confused!

 

[Haut Medoc]

Re: Won't rev up?

I checked the seal when I draind the tank and it was and still is good as far as I can tell. I also replaced the breather and it sits about 2 feet above the water line.
I'm still confused!

I'm with Don, there are only two ways to get water in there, through the fill cap or the vent.....
You could try to pressurize the tank & listen for an air leak.....
Or the gas itself comes with the water in it.....
I'm gonna go with a bad fill cap though......