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OMC Cobra 3.0L problem

T

tylerlee001

New member
Hey all, i just bought a 89 four winns with the 3.0l OMC. It ran great for the first 3 runs this year then a new problem popped up. Once the engine gets above 150 degrees (assuming F) it starts misfiring. I initially thought it was fuel, so i drained the tank empty and added fresh fuel with Sea Foam. I ran the engine, same issue. Runs great for 10-15 minutes,then starts misfiring/surging. You can feel the boat surge as it does it.

I replaced the fuel filter (dirty), clean the air intake (i have no idea how it ran). After i saw the filter, i check the plugs and sure enough the front 2 were black and the rear two were okay. replaced those with new and it does the same thing.

Is it running to lean when the engine heat builds? Do you think it needs to have the fuel turned up on the carb? It dosent produce and smoke or anything like that.

Im totally lost guys, I appreciate your help.

Thanks

Tyler
 
Follow the fuel hose to the tank unscrew the fitting that enters the tank that fitting is a one way valve. Up will come the fuel pickup tube on the end of the tube may be a screen clean it.

Me i would run the boat on a external tank of gas.

If it's still present the problem i think ypu need a carb rebuid.
 
tylerlee001 said:
also should add, that when it is missing, when i got to trim the boat, its run even rougher. Im sooo lost...lol
Click to expand...


This last comment could be a good clue, you may actually have a bad coil like hystat suggested or you could have a bad connection causing a high resistance short. I would check the battery cables at each end, clean and tighten them, the tilt draws a lot of power and could be causing the ignition to be under voltage.
 
Could be coil, but what i find is that all is good for 15 min. the dirt get sucked up on a filter say in the tank pickup tube. Then the motor is starved for fuel. Shut her off the dirt falls off the screen and it does it over and over.

I should have also posted while he has up the tube to suck all the gunk off the bottom of the tank.

Could also be a screen in the fuel pump, or the screen in the fitting that enters the carb.

Fuel water sep element clean if equipped with one.

I just reread the op twice.

Could the riser be bad ? Bear with me a second. Heats up and a crack opens in the riser, now we have water getting in the back 2 cylinders ?

Wouldn't show up in the oil.

How is the oil ?

I had a problem close to yours. Behind the neck of the t-stat housing developed a hole in the head between the water passage and the pushroad hole, head went.

So if after trying Hy's and my suggestions, motor is timed correctly weights good.

Then riser, bad, and if you discover water in the oil then we can start looking for the cause.

Vent clear, maybe critters or kinked vent hose ?
 
Last edited:
Lots of good suggestions. Ill Check the fuel lines, battery connections to the coil. I may be able to get a new coil and see how that works.

Theres no fuel water sep. The oil looks good, but i have drained it to check either. Would the filter have water in it if that was the issue.

Thanks guys, ill keep ya posted.

Cheers!
 
Sounds just like my 3.0 was doing. Run fine till coil warmed up then down hill from there. Put new coil on and away it went.
 
I checked the fuel lines, they are good, no bends. Fuel is fresh as of yesterday. I replaced a selanoid that was broken, and I just replaced the coil to see how it works and im heading to the dock now to launch. Ill let you know how it goes. Thanks again guys.
 
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