Poor Power 5.7 OMC Cobra

[HuntFishLive]

I have a 1989 5.7 Cobra OMC on a 225 Four Winns Sundowner. It has ran flawlessly for 5 years and last week it died cold turkey as if it ran out of gas. It would not start.

There was half a tank of gas but would not start. I had a mechanic friend check it over with me and found that the points were shot. We replaced the points, distributor, condensor and plug while we were at it.

The engine fires up perfectly and idles like a dream. Thought we had problem solved. Then we gave it a little throttle and at 3000 RPM's it loses power and starts to flutter a bit. Decided to try it on the lake and there is no power out of the hole at all. It does not stall out and if you back it down it idles perfectly.

We replaced the fuel filter and the condition has not changed. Any ideas?

 

[HT32BSX115]

Re: Poor Power 5.7 OMC Cobra

Howdy,


Take a look at the fuel pick-up screen in the tank. and the fuel vent. If either are clogged or partially clogged, fuel flow will be restricted enough to cause power loss above idle.


Welcome aboard!


Rick

 

[bubbz]

Re: Poor Power 5.7 OMC Cobra

I may be off, as Im new to the boat world, but I took my formula f20 out last week for a first trip and had the same problem. Have you checked to see if your timing is set correct. Mine was out and would act the same way. I set it with the timing light and its fine now except the oil leak that poped up yesterday... hope this helps you...

 

[HuntFishLive]

Re: Poor Power 5.7 OMC Cobra

Yes the timing and points have been checked and rechecked and set to spec.

We are contemplating replacing the fuel pump?

So where do I find the fuel pick up screen and vent on the gas tank?

 

[HT32BSX115]

Re: Poor Power 5.7 OMC Cobra

Yes the timing and points have been checked and rechecked and set to spec.

We are contemplating replacing the fuel pump?

So where do I find the fuel pick up screen and vent on the gas tank?

It might be a good idea to test the fuel pump instead of blindly replacing it. If the fuel pickup screen is clogged a new fuel pump won't help either.

The best way to get to the screen in most tanks is to pull the tank gage sender and you'll be able to see in there with a flashlight and a small mirror.....the screen itself is on the end of the fuel pickup tube. which can be removed right from the top of the tank.

The gage sender is usually near the fuel pick up line. You'll have to find it if it's under the floor or deck etc....

On most newer boats there's also an "Anti-Siphon Valve" which is just a simple ball/spring check valve screwed into the pickup line coming from the tank that is known to either clog with debris (that gets past the screen) or varnish etc.

You can buy it right here on iboats http://www.iboats.com/Anti-Siphon-V...6136179--**********.715274956--view_id.392107

The vents are usually a tube welded into metal tanks and have hoses that go from them back to near the fuel fill. If the vent is plugged, the boat will run fine until a vacuum is produced in the tank that the fuel pump cannot overcome.

 

[HuntFishLive]

Re: Poor Power 5.7 OMC Cobra

Ok. Will check into that and see if that might be our issue.

One last detail that I am not sure makes a difference. When I water tested it the RPM gauge fluttered between 4-5 grand. However the engine was totally bogging down and certainly was not "winding" out. I did not even have the throttle half way down.

Does that indicate more of a ignition issue than fuel??

 

[HT32BSX115]

Re: Poor Power 5.7 OMC Cobra

One last detail that I am not sure makes a difference. When I water tested it the RPM gauge fluttered between 4-5 grand. However the engine was totally bogging down and certainly was not "winding" out. I did not even have the throttle half way down.....Does that indicate more of a ignition issue than fuel??

Possibly, or the tach or associated wiring is faulty.