1989 Cobra 5.0 Keeps Cutting Out

[JJ Jenkins]

Last season my 89 19' sunbird with a 5.0 OMC Cobra starting cutting out about 45 sec after getting on a plane (and still does today). She cranks, revs, idles in neutral and will creep in gear at about 2000 RPM all day. As soon as I push the throttle to the floor, she'll jump on a plane, run for about 45 secs, bog, then cut off. Then takes a minute of cranking or sitting for a few minutes to clear the flood? When I pulled the plugs, they were fouled pretty bad, wet and black, so i assumed flood...
The simple fix I thought of was the anti-siphon valve - replaced it, then started throwing parts at it for the past 12 months - same results! To date, she has a new anti-siphon valve, fuel line to filter, new filter/water seperator, new fuel lines to fuel pump, took apart and rebuilt fuel pump, new line to carb, new rebuilt carb, new alternator, new coil, new distributor cap, points, rotoe button, spark plugs and plug wires, and new battery! I tuned the new carb to specs and adjusted the timing to specs as well -She runs as smooth as ever in nuetral - put her in gear, catch a plane - same problem!
After I just changed the plugs, I pulled the #1 and it had a little oil on it, but nothing bad - and she doesn't smoke... I am stumpped! I do notice that when i trim the stern drive all the way up while the engine is running, she idles/revs rougher and higher as the trim comes toward the top of the water - Is this normal? Also about 90% of the exhaust bubbles come from under the cowl section of the outdrive close to the stern instead of the prop (I know ther is some holes in the bottom of the main exhaust boot/hose - Is this normal (could it be a back pressure issue?)
What else could it possibly be?? Any help is MUCH APPRICIATED - I don't have much hair left to pull out!

 

[Kerrpapa]

Re: 1989 Cobra 5.0 Keeps Cutting Out

JJ,
I have a 87 25' Regal with a 5.0 OMC Cobra and I am having the same problem. I haven't noticed the trim issue, but a carbon copy of the cutting out problem. I too have not be able to solve this problem. We are in the same boat (sorry, couldn't resist ).

I hope someone can help us with this.

 

[Bridar]

Re: 1989 Cobra 5.0 Keeps Cutting Out

Have you checked for an obstruction involving the pickup tube in your fuel tank? It's a rare occurance but a possibility.

 

[jerryjerry05]

Re: 1989 Cobra 5.0 Keeps Cutting Out

If it's happening when you trim or tilt.There is a shift interupt modual.It's activated with the shift cable.That could be part of the problem.
If the cable or shift mech gets sticky or gummed up.It makes the shift assist work when it ain't supposed to.
Start with the drive,remove and clean the shift mech on the transom assy.
Get a parts diagram.Then look for the BELLCRANK.Binding there can cause that.Then check the shift cable.
Unhook the shift assist(usually on top/back of the motor)See if that makes a difference.J

 

[ljsweeney]

Re: 1989 Cobra 5.0 Keeps Cutting Out

Have you checked your fuel tank vent tube?

If it's partially clogged, the increased fuel demands of WOT could be creating a vacuum in your tank, causing a fuel starvation issue.

Good luck.

 

[Big_Eddy]

Re: 1989 Cobra 5.0 Keeps Cutting Out

You say you adjusted the timing to spec - Have you confirmed that your timing is advancing when the revs increase? If the timing does not advance, the spark won't trigger soon enough, and it will run poorly if at all. Go back to low revs and the advance is correct and it will run fine all day.

Assuming the same distributor setup as mine, remove the plate holding the points and condensor and check the advance weights and their springs. Then use a timing gun to confirm the timing advances at speed. If with any setup - check with the timing gun first, then go from there.

Big_Eddy