Omc king cobra 5.8l stalls above 4000 rmps

[TranzinCT]

Hi,
I recently purchased a 93 Four Winns Vista 245 with an OMC King Cobra 5.8L. The engine has only 253 hours on it, runs great at idle and up until it reaches 4000 rpm, that?s when a problem occurs. When, I suddenly open the throttle, the engine flawlessly increases power and the boat plains. As soon as the tachometer goes over 4k rpm the engine hesitates, does not stall out, but returns to below 4 rpm and remains at that level with smooth operation, when increasing throttle again, the engine has no power and hesitates, but does not die. When I turn off the engine wait a few moments, start it back up and gunn it, the engine gains massive power for about 30 seconds, going well over 6k rpm, boat increases speed, and drops back down to about 4k rpm again. Thinking it would be a carburetor issue, I had the carburetor completely rebuild and same issue persists.
Compression and spark is fine on all cylinders.
One thing that I wanted to mention is that the previous owner has not used the boat for about 2 years, it was in his back yard.
I am new to inboards, always ran a outboard engines, can anyone please assist???

 

[HT32BSX115]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Howdy,


Assuming that you have checked fuel filter, fuel supply (fuel pickup screen, fuel tank vent), spark plugs, etc......You may have an ignition problem. Being a 93 "King" Kobra, does it have the dreaded "Spitfire" electronic ignition installed?

 

[Bondo]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Assuming that you have checked fuel filter, fuel supply (fuel pickup screen, fuel tank vent), spark plugs, etc......

Ayuh,... I agree, it sounds like a Fuel delivery issue...

 

[HT32BSX115]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Ayuh,... I agree, it sounds like a Fuel delivery issue...

Yeah. and what about this?

When I turn off the engine wait a few moments, start it back up and gunn it, the engine gains massive power for about 30 seconds, going well over 6k rpm, boat increases speed, and drops back down to about 4k rpm again.

First of all, you are not really running the engine at 6000RPM are you?

You could only do that in neutral. Very bad to do that. It also doesn't tell you anything....... unless your tach is completely out of whach , OR your ignition system RPM limiter is either not working or (it doesn't have one)

The 5.8L "King" is a Spitfire ignited engine. I am pretty sure that they incorporated an RPM limiter in the system.

If yours IS REALLY a 1993 "King" Kobra, it probably does have the Spitfire system. If it's screwed up, you'll be buying yourself a new marine distributor. There's few or no parts available for them unless you can find a dealer with a ign module sitting on the back shelf collecting dust. (of course he'll want your first born child for it and won't take it back if it doesn't work!!!)


GO to the following link to find your engine/drive model number and look for parts (if they're still available)

http://shop2.evinrude.com/Index.aspx?s1=tr3diomo0o96dt7pa721o5jdr2&catalog_id=0&siteid=1

click the drop down menu and select "STERN DRIVE" and find your year, model etc.....

 

[JasonAych]

Re: Omc king cobra 5.8l stalls above 4000 rmps

I had the same symptoms on a 1993 Mercruiser with a 4.3. Ended up water in the fuel tank and of course a new filter/separator.

Begs the questions, how did water get in there? I bought it with the issue. The guy I bought from kept it at a dock and used marina fuel. From what I understand, it is more common for them to have water in their tanks. This was based on word of mouth talking to folks.

 

[HT32BSX115]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Water can get into a fuel tank either by the owner putting it in (contaminated fuel) or if the cap leaks and the boat sits out in the rain.

Condensation is not all that likely. http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

 

[Bondo]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Water can get into a fuel tank either by the owner putting it in (contaminated fuel) or if the cap leaks and the boat sits out in the rain.

Ayuh,... Orrr,... an improper Vent line installation.....

I've seen Alot of 'em,...
The vent line at the hull fitting MUST loop Up, before it drops down to the tank fitting...
Otherwise, water Gusts through it into the tank from splashs, waves, etc...

 

[ddbaran]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Same problem here. I have a 1994 Fourwinns 210 Horizon with 5.8L OMC Cobra SX drive. Owned it since brand new. Has probably at least about 500-600 hrs on it.

Tore into it tonight for the nth time. Finally started taking the fuel tank apart one piece at a time, and I found the fitting at the top of the fuel tank was corroded so bad it broke off in my hand. I think it was leaking air and causing a fuel shortage under load. It normally ran fine at idle and while in no wake areas, but it would really bog down and lacked power when I put it all the way to WOT. When under load and trying to get on plane, it would only get to about 4000 rpm or less and sometimes alot less with a boat full of people. The other thing that was puzzling and I think this may also be the culprit is that after a long run then sitting at the sand bar or dock or whatever for a while, we could smell gas coming from the bilge area under the engine, but we could never find where it was coming from; never could see anything and it went away in a few hours. We never found any fuel accumulated in the bilge or anything. Each time it was probably about a couple teaspoons that would leak out. This leaking fitting may explain it because the crack was above the check ball valve. So instead of the fuel being able to drain back to the tank, it leaked out on the top of the fuel tank and was causing the fuel smell. I saw some evidence of fuel residue on top of the fuel tank around the fitting area, so at least that is what I suspect was going on.

What I did was replace the barb fitting on the fuel hose which was attached to the fuel pickup tube. The original fitting was white metal or galvanized and had a check ball inside of it. It was made from some odd type of material that had corroded over the last 18 yrs. I replaced it with a standard 1/4" thread and 3/8" barb brass fitting from Home Depot. So far at the dock it seems to be fine. Need to go out in the daylight and check one more time for leaks and then take it out to the lake tomorrow for a full WOT load test. I'm hoping that was all it was and now I fixed it. I don't think eliminating the check valve is going to make any difference. We will see how it goes. If that check valve is important and makes some difference, then I will find another brass inline fitting instead of the crap fitting that was on there from the OEM.

Update: Motor ran outstanding and jumped up on plane without any problems. It was nice to actually find something and fix it and get back on the water finally. It felt almost like a new motor again.

Cheers!!!

 

[bigike]

Re: Omc king cobra 5.8l stalls above 4000 rmps

Could you get a fuel pressure gauge and hook it into the fuel rail? Have someone monitor the pressure, if it drops then you have a pickup problem. It is fuel injected right?