OMC Runs rough once warm

[marroan2]

I have a 1984 OMC 5.7L I/O in a Celebrity. The engine starts and runs great. After running around the bay for about 20 minutes it started to run rough and quit. Progressively getting worse that it wouldn't start. After the boat sat for an hour on the trailer it started and ran great. I checked that the Choke is opening and changed the fuel filter and Water separator. It started and ran great but after about 20 minutes it started to run rough, and when you decelerated it wanted to quit. I'm trying to fix the problem before going out again. The boat sat for 2 years prior to this. Stabilizer was added to the fuel each year.

 

[float2]

Re: OMC Runs rough once warm

What carb do you have? Can you get up on plane smoothly or does it studder? Can you maintain plane without surging? Possible that you have an obstruction in the carb maybe a clogged squirter? Fuel pump? Plug wires and coil wire tight? Sitting for long periods of time without use is one of the largest causes of problem for boats.

 

[marroan2]

Re: OMC Runs rough once warm

Rochester Quadrojet. when I left the dock the boat ran great got up on plane. I cruised around for about 20 minutes with no problem. Then it started to progressively run rougher. If I tried to accelerate or decelerate quickly it would stall. I was able to run a few more minutes at idle before it would quit. then it got to the point that it wouldn't start. I checked all the wires they all are on properly. As stated earlier after the boat sat about an 1 it started and ran good, but after running a while it started to get rough. It appears to be a fuel problem, I just can figure out why it runs great for a while and then gets to the point of not being able to start. If the fuel was bad from sitting I would think it would run rough all the time.

 

[airdvr1227]

Re: OMC Runs rough once warm

If it really sat for a couple of years you coud have some water or other nasty gunk in the tank. I'd start with some fresh go-juice.

 

[superbenk]

Re: OMC Runs rough once warm

Make sure you fuel tank vent isn't clogged & also check/replace your anti-siphon valve. You may be getting into a starved fuel state after a bit.

 

[Howard Sterndrive]

Re: OMC Runs rough once warm

a bad ignition coil will act like that too sometimes.

 

[marroan2]

Re: OMC Runs rough once warm

I disconnected the fuel line from the water separator and hocked up an external fuel tank with new fuel. Also check the coil it tested okay but I replaced it with a new one I had. After running for 15 minutes the engine still starts to run rough. The choke is opening and the accelerator pump in the carb seems to be functioning correctly. Any other recommendations

 

[sethjon]

Re: OMC Runs rough once warm

What carb do you have? Can you get up on plane smoothly or does it studder? Can you maintain plane without surging? Possible that you have an obstruction in the carb maybe a clogged squirter? Fuel pump? Plug wires and coil wire tight? Sitting for long periods of time without use is one of the largest causes of problem for boats.

Plug wires and coil have no effect if heat is a problem. Sitting for a long period could be a problem but cold or hot, not just warm.

 

[sethjon]

Re: OMC Runs rough once warm

a bad ignition coil will act like that too sometimes.

True but doubful.

 

[Howard Sterndrive]

Re: OMC Runs rough once warm

might try a run with the ESA module unplugged.

 

[full stringer]

Re: OMC Runs rough once warm

man i bet his float is sticking in the carb! take off your float bowl/bowls clean and replace the needle and seat valve/valves depending on 2 or 4 bbl?

 

[dubs283]

Re: OMC Runs rough once warm

sat for 2 years??

time for a full-tune up including all fuel filters (there is one in the carb too)

plugs, wires, cap, rotor, points set/condenser, set dwell/timing/idle, check carb operation...few things to do

also, as stated - check fuel lines, pick-up, anti-siphon valve, tank vent, debris...