Logo
FULL SITE MENU

3.0 omc running real rough

A

ajmartin67

Member
i have a 1984 3.0 omc, my problem is this. in the driveway on the muffs, the engine runs as smooth as can be, today i took it out on the water and it ran real good for about a min, then it started coughing and sputtering real bad and died, i started it up and it was idling real rough, then after 20 min it started running as smooth as can be for a min or so then started running real rough and would not get over 5 mph, i have new clean fuel, new spark plugs, new distributor and rebuilt carb last year, could it be the carb again? or the ignition coil?
 
ok lol after i asked how to set the points i felt stupid, after i took the cap off i remembered how to do it. the gap was fine. really what it feels like to me is that i am picking up water through the intake side of my manifold, which possibly would explain why it runs good on the muffs and runs like crap on the lake?
 
well let's start with the basics. Pull the plugs, they look like what? Compression test.

All is good ? Then a tune up, time it. Still have problems?

Then it's time to start at the fuel tank pull the pickup and suck the junk off the bottom of the tank.

Clean filters, and run it. Still doing it ?

Then carb rebuilt and run it. Still doing it then your missing something.

Ok riser changed when? Saltwater ran, then every 5 years. But the plugs will tell you if your getting water in.

No water in the oil then your half way to knowing if your getting water in.

Do the above and post back whatever you find we will go from there.
 
ok compression test is in the 120 range on all 4 cylinders, spark plugs look ok. i checked the pickup tubes on the fuel tank. they were free and clear, i checked all fuel filters, they were all good and clean being as i put them on a month ago or so, now as far as the riser, i dont know when that has been checked last, would that contribute to my real rough running? there does not appear to be any water in the oil, however i am going to check fuel pump pressure, any other ideas?
 
You checked the filter at the fitting that enters the carb? The filter in the fuel pump ?

If yes and clean, run it on a external tank of clean fresh fuel. If you still have problems. Then a carb rebuild. Still have problems ?

Pull apart the 2 esa plugs, do it on open water run it. If the problem went away post back.

Fuel pump should give between 4-7 psi.

Post back anyway keep us informed we can go from there.

Question what else does the motor do, thats not normal ? I don't want to make suggestions, i want you to pay attention to all the gauges and post back if there is anything else the motor does, thats unusual.
 
yes i checked all filters ran new gas with new tank, i went ahead and rebuilt carb, i started it up on the muffs in the drive way and same thing coughing and sputtering, and the engine started running real hot, im really at a loss here oh and i did un plug the ESA and still it made no difference
 
you never till the end post said it ran hot.Real hot is what you posted, not for nothing but do you think that would be a good thing to tell me ?

OK,Ok i'm good not pissed, miffed yes not pissed.

Ok i already wrote about the riser, but i didn;t write about the t-stat. First check or replace, or take out the t-stat for now. Then run it fixed ?

Still running hot then maybe you got a bad impeller.

Take the hose off from the t-stat that runs from the transom. Put water to the drive and see how far straight up the water shoots.

8-12 inch's then you got good water to the motor impeller might be good.

Pull the riser and see if a flapper/shutter fell down in the tube.

The riser still good?

See if your motor can't exhaust it can't run.

How really hot ?
 
sorry that i did not mention the temperature earlier, up until today it has been running around 160 and today it was over 200, i will check the water coming to the motor, i checked the riser and did not see any flapper in it anywhere, what should it look like? i do have the head pulled off right now and did find a partial blown head gasket
 
it look a little like a rubber toilet flapper in the tank. It's should be in the exhaust tube. Mine didn't come with one. And there is no provision for one on mine.

Shine a light down the tube. And with the drive all the way up i can i can have my son stick his hand up the exhaust tube, and i can see his hand when i look down the tube from inside the boat.

You have a mirror on a stick, you could stick that up from the outside.

Yours could be the same thing.

Riser looks like what on yours.

I have a 1986 boat 1985 drive. Same as the 1984.

Blown head gasket, would do it, your compression was what ?

T-stat bad, riser bad, or impeler bad, to make it overheat.
 
ok so here is another question, i looked for the flapper in the exhaust, i found where there used to be one, there is just a little of it left, is it hard to put in? and is it essential to have one? would this be part of the reason it runs poorly?
 
Back
Top