OMC 5.0L Cobra Stalling At Speed

[daman4469]

Hi all,

I have a 1990 Sunbird Corsica 19.5' with an OMC 5.0L Cobra, with Cobra outdrive. This engine has been running great; sounds good at home, idles well, sounds good at speed. Just had timing/carb adjusted at local shop. Runs sweet. However, yesterday on the lake, problems arose. When idling, it is fine. When I get on it (to get up on plane), it would start to go, then shut off as if I turned off the key. It would then start right back up. After a while, I would be able to get it going. However, I could hear it hesitating, then hitting WOT, then hesitating some more. It seems to me as if its not getting fuel....I may want to check the fuel filters, as I have read this engine has several. It seems to me sometihng is clogging the filters, then falling away, allowing me to get on plane then. Before I go ripping in to anything, I figured I would see if anyone out there has some tips/ideas. Caught me off guard as it ran flawless two days prior...very sudden onset.

Engine running at good temp (1/3 of the way up the temp gauge)
Idling at 550 rpm
When running smooth, WOT is 4200 rpm.
When I engage the neutral switch and rev engine, it revs fine. Just seems to be happening under load.

Thanks all!

 

[mcleaves]

Re: OMC 5.0L Cobra Stalling At Speed

Sounds like fuel starvation to me, except wheere you said it shut off like someone turned the key. That sounds electical. Check your hoses and clamps. Also your electical connections. Perform a wiggle test on them while it's running

 

[daman4469]

Re: OMC 5.0L Cobra Stalling At Speed

Yeah, I shouldn't have said about the key, because its not really like that. It just reminds me of riding my dirtbike when it was running out of gas. Sputtering, etc. Did find a loose connection on Distributor cap, but that wasn't the issue. Its hard to hear what the engine is actually doing because of the water splashing around, etc, but once I got it up I could def. hear it struggling.

 

[mcleaves]

Re: OMC 5.0L Cobra Stalling At Speed

Well I would start with the fuel system then. Check all your hoses and clamps. Make sure your fuel tank vent is clear. Change those filters.

I know you said the carb was just serviced. Maybe the float is not set right or is sticking.. I chased a problem like this for months many years ago. I was convinced it was not something I did. I had replaced the fuel pump and rebuilt the carb. I checked and double checked the fuel lines probably 10 times, as people were telling me to do. Spent all kinds of time screwing with the ignition. Turns out I had a loose clamp back at the tank. I had NOT worked at the tank, but in replacing the fuel pump I had moved the hose and it broke the "gummed up" seal that was keeping it airtight. Two turns of a screw driver and I was off and running. Look at the simple stuff first, and look at ALL of it.

 

[daman4469]

Re: OMC 5.0L Cobra Stalling At Speed

Thats good to know. I replaced the main fuel filter, but I know there are several. I'll do that first. Never would have thought to check for air-tight ness. I might spend next Saturday just going over everything, instead of the 'try one thing, test, try another thing, test' method. Just do it all in one fell swoop!

 

[daman4469]

Re: OMC 5.0L Cobra Stalling At Speed

Just an FYI for you all, I took the entire fuel system apart today. Filters were all good....carb was full of gas, as were all the filters and fuel pump. Took carb apart and found both jets were clogged, almost completely shut. The return hose from carb to fuel pump was also gummed up and clogged. Cleaned both out, ran like a champ....even getting about 4 MPH more top speed too. Did something right!

 

[mcleaves]

Re: OMC 5.0L Cobra Stalling At Speed

Glad to hear it!

 

[daman4469]

Re: OMC 5.0L Cobra Stalling At Speed

I actually was wrong. The problem came back, again, only when warm. Troubleshooting took weeks. Replaced igntion stator under Distributor cap (was burnt from heat) and issue is resolved. Turns out this was a big issue on Ford motors.