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Omc cobra intermittant rough running

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nealy8112

New member
"I have a 1988 omc cobra w/ a

"I have a 1988 omc cobra w/ a recently rebuilt 350, new 4bbl, recent tune up. The engine starts fine and always runs great and strong for about 10-20 minutes then delevelops an intermmtinat problem where it starts to backfire lightly thru the carb and then it will begin to sputter and lose power but never dies unless i bring the throttle back to idle. The engine will run rough for a few minutes and then all of a sudden it bursts back to life, runs fine for a while then start losing power again. I tried gas drier in the gas but dosen't seam to help. Does this symptom sound familiar to anyone?"
 
What kind of distributor (

What kind of distributor ( points or electronic breakerless )? What ignition parts were replaced in your recent "tune up".
 
"unfortunately it has points,

"unfortunately it has points, the points cap rotor and plugs are about 8 mos old. A look at the points showed no signs of pitting, the plugs looked clean with a light tan color. I will replace the cap, rotor and points and see what happens. I was just wondering if that kind of completely erratic running was more typical of
water in the fuel system."
 
"Before You start changing par

"Before You start changing parts do a test by disconnecting the shift module. Be carefull, do it in open waters and stop the engine before taking it out of gear."
 
"Yes, it sounds like a rare sy

"Yes, it sounds like a rare symtom of a weak coil.
I would suggest though that you sould change out the condenser and see what that does. If it is the same then change the coil. When changing the coil be sure to verify if you need one that needs external ballast or is one that does not."
 
"It is a 9V coil but the balla

"It is a 9V coil but the ballast/resistor is in the wire, not a separate unit. It was a service memorandum out on certain models to shorten the wire but only if the engine suffered misses on high rpm's. If You eplace it with an 'unoriginal', be sure to get one with a 'high' center getting maximum distance from the primary and secondary entry/exit. Have seen too many replacements where spark jump to the primary has been the reason for burned contacts and condencers, may even kill your tach!"
 
"I will try disconnecting the

"I will try disconnecting the shift assist module first, then the spark jump issue sounds interesting. It is possible this is an automotive replacement coil. I did notice my tach jumps high when i switch the ignition on.Is there any way to test for spark jump? Which wire has the ballast built-in? I know the wire from the positve coil terminal to the distributor has been replace with plain wire."
 
"If the + wire have been r

"If the + wire have been replaced with a std cable, you are running 12V 'system' on a 9V coil!
Install a ballast resistor unless the coil has been changed too."
 
"i did replace the fuel/water

"i did replace the fuel/water separator filter first. I emptied the old filter and brown gunk came out, so i am guessing that was the problem. I will give it a good run this weekend and see...."
 
"If You filter was full of dir

"If You filter was full of dirt, you better take a look at the tank as well before you start running again. Take out the fuel gauge, unless You have an inspection hatch/opning. Put a copper fuel pipe into Your oil suction pump, have the boat 'tilted' so one corner of the tank is low, let it rest for some hours, and suck up until clean fuel comes out. Top up with new fuel."
 
Note that you may have another

Note that you may have another problem 'mushroom' valves. To check for that You will have to do a compression test.
 
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