OMC 5.0 Cobra

kylejb2663 · Jun 4, 2012

Got a engine question for you guys.

I took the boat out this weekend, first time I have been able to WOT with both engines. Everything seemed great, good water temp, oil pressure, etc. Did I mention I also got to FILL the boat with gas LOL - :facepalm:

My friends and I were practicing docking because I am trying to learn how to use the twin engines to maneuver into tight spaces. All of a sudden my port engine dies and would not restart- Previously, before it did we noticed when it was in reverse it was clunking really bad, almost sounded like a backfire it's hard to describe, however at low RPMs in reverse it didn't clunk.

My home dock location is on my port side so trying to that boat into it's dock space using the starboard engine was not very fun.

The only thing I am thinking is possibly the motor is not getting gas and the fuel filter is clogged. I got water in my tanks last year and they cleaned em out and threw some K100 into them, I have heard this stuff can clog your fuel filters because of all the crap it cleans out... What do you guys think?! :

indybleck · Jun 4, 2012

Re: OMC 5.0 Cobra

Just went through this myself although mine didn't clunk it just sputtered and died. I pulled a spark plug out and noticed it was dry no fuel, then I back tracked to the tank. One quick check to see if it's not getting fuel, I started the boat with ether and it ran so that was another clue about fuel delivery problems. I just updated a thread I started it's titled Got the boat out of storage.

kylejb2663 · Jun 4, 2012

Re: OMC 5.0 Cobra

Thanks indybleck! I just checked out you're thread, I'll replace the fuel filters and the carb filters and see what happens. I'm hoping that all it was! Maybe I'll carry a few fuel filters on board for cheap insurance, LOL

kylejb2663 · Jun 18, 2012

Re: OMC 5.0 Cobra

Alright so I replaced the fuel filters and the motors are running but they are still hesitating like crazy- They do start easier now with the filters-

One of my friends took a look at it and said I need new Carbs right off the bat, he said it looks like have not been rebuilt in ages. My question is if I buy the rebuild kits for these, how hard is it to rebuild them and replace the float.. Is there anything else I should order and replace while in there.

kylejb2663 · Jun 18, 2012

Re: OMC 5.0 Cobra

Forgot to say that the carbs are Rochester Quadrajets

Howard Sterndrive · Jun 18, 2012

Re: OMC 5.0 Cobra

you also may want to observe the lower shift cable and ESA switch operation as you shift (in the water) - that rough running issue description sort of sounded like an engine being "stumbled" by the electronic shift assist module due to a sticking shift cable or maladjusted microswitch.

kylejb2663 · Jun 18, 2012

Re: OMC 5.0 Cobra

Excellent idea! where can I find the ESA microswitch to test it?? I know the cables were just replaced and they are the new red style cables... however I can't say they were done correctly cause I did not own the boat at that time.

Howard Sterndrive · Jun 18, 2012

Re: OMC 5.0 Cobra

I wouldn't normally link to another board, but this is pretty comprehensive:
http://www.marineengine.com/boat-forum/showthread.php?293383-OMC-Cobra-ESA-switches

kylejb2663 · Jun 19, 2012

Re: OMC 5.0 Cobra

Thanks Howard I really appreciate it!!!! Extremely detailed!!! I will check that out tonight-

My friend and I actually took the boat out on the water last night and the port motor died again when I am shifting a lot (docking)- However if I am running WOT or just in forward gear it never dies at all... There is no stumbling either. When I put it in reverse there is a extremely loud clunking like the motor is backfiring..

I did seem to have some problems getting it on plane yesterday- I had the trim tabs all the way down and I could only get it up to about 3100 RPMs whereas a few days ago I was at 4000 RPMs I believe and brought it down to 3200 for a cruising speed... Any ideas??

kylejb2663 · Jun 19, 2012

Re: OMC 5.0 Cobra

I should add that when the motor does actually stall out from the docking/shifting. I have to place the throttle ALL the way forward while starting to get the motor re-started. It will not simply restart with a key turn or restart if I pump the throttle several times.

kylejb2663 · Jun 21, 2012

Re: OMC 5.0 Cobra

Update:

Last night, I did check the ESA and it does stumble the motor but sometimes it stalls the port motor... Carb issue?? It does seem like the idle is extremely low on the one engine but I always heard you should not have to adjust the idle screw unless there is a carb problem- it should not change from when the carb was installed and tuned..

Any ideas anyone?

indybleck · Jun 21, 2012

Re: OMC 5.0 Cobra

I adjust idle when I tune the engine, change points, condenser. After that I have to re time and then set the idle.

kylejb2663 · Jun 21, 2012

Re: OMC 5.0 Cobra

I'll have to check that out- I still have points I was going to order the Delco Voyager system but never got around to it- I wanted to replace the points, plugs, wires, and condenser. I'm exactly sure on how to work with points though or use a Dwell Meter. I figure if I re-build the carb, do the tune up and set the idle that everything should be running smooth- What do you guys think??

indybleck · Jun 22, 2012

Re: OMC 5.0 Cobra

In theory it all should work, but you know Murphy's Law.

kylejb2663 · Jun 25, 2012

Re: OMC 5.0 Cobra

LOL Absolutely... Well I had a new found discovery yesterday- When you open up the engine bay covers the engines get up to max RPM... when they are closed, they do not..... Weird... what could cause this??

jarrod1995 · Jun 25, 2012

Re: OMC 5.0 Cobra

My tube on my intake side for my blower was completly plugged by your freindly little mice. Surprised it didn't blow up, I was running it, but it wasnt bringing in fresh air. I wish mine was that sealed up that it could be needing air.

kylejb2663 · Jun 25, 2012

Re: OMC 5.0 Cobra

LOL Yeah mice are not fun!!! I think I may have figured out what's going on.. When they painted my boat they had to take the four vents on each side off- when they put them back on I think they put them on wrong (upside down) and it was actually deflecting air and acting as a vacuum to suck all the air out of the engine room. So I turned em around now it's time to sea trial and see if it makes a difference...!! LOL - Anyone hear about something like this making a difference??

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