Cobra Runs Well, but eventually stops and wont start

[wills-ggl]

Hi guys, MERRY CHRISTMAS<br /><br />i have 1989 OMC cobra based on the 5.0 HO ford engine.<br /><br />I have a interesting problem which I'm having difficulty understanding.<br /><br />Right now the engine runs brilliantly. Smooth punchy and responsive. From a mechanical perspective the engine is in very good shape. <br /><br />However i am experiancing a gremlin.<br /><br />I can run my motor long periods 20minutes plus on the trailer and everything is good, starts easily when cold and hot.<br /><br />I had lauched my boat in the river yesterday, and now i have problem which i dont think i can get rid of. <br /><br />Boat ran for a hour, cruising comfortably down the river at around 2500 RPM for the whole time. this was happening for about an hour, i then backed of the gas to pull back to shore, the engine stalled. mind you the engine was running well up until this point. Water and oil pressure was good!!! and i was stopping and starting during this period as well because we where wakeboarding.<br /><br />The engine stopped and from that point on wouldnt start at all, the engine was cranking well, but just would not kick over at all. <br /><br />So i pulled the boat out of the water and took the boat home for a look see. Found nothing wrong, i though that the coil was gone, so went out and sourced a new coil. Decided to start engine with old coil to be sure, but in the time it had cooled down, the engine fired backup and was running again. <br /><br />I dont think its a fuel supply issue, as i took the flame arrestor off and it seemed like i did a good job of flooding the engine in starting attempts.<br /><br /><br />I spose the wierd thing is that i could walk out to the boat right now turn the key and it will run fine. But i have a rather painfull problem which means i will find myself being towed to often back to the ramp or my house to fix the issue. <br /><br /> I have good basic knowledge of engines and mechanics <br /><br />I guesing it is heat related but i cant figure what would be effected but it???

 

[shelikesit]

Re: Cobra Runs Well, but eventually stops and wont start

I'm not a mechanic but may be able to shed some light from what these guys taught me. When you shut the motor down or it shuts down on it's own something isn't stopping the gas they way it should.<br /><br />Enough gas should drop in the carb for restart after the key is turned off. Also gas should be right outside your carb, stopped.<br /><br />What was happening with me was after it stalled or I turned it off gas was dumping into the carb and also siphoning back to the fuel pump. This did 2 things, it flooded the carb and also made it so that the fuel pump had to double time it to get gas back up to the carb.<br /><br />I found a gas leak that solved the siphoning problem and had the carb rebuilt to stop the flooding. Both things seemed to help my problem.<br /><br />This may help you, especially being that it's Christmas morning and the smart ones probably set this "love" aside for the family. At least one day out of the year they "might". I honestly planned to but.............................<br /><br />Merry Christmas.

 

[Haut Medoc]

Re: Cobra Runs Well, but eventually stops and wont start

It does sound like a fuel issue to me....Have you tried opening the throttle all the way & leaving it there.....(Not pumping) & then cranking?...Also, check to see if you have spark present when this happens....A coil will quit when it gets hot, when its on its way out....It could be a heat sink issue with the coil....Put the new one on & see if the condition persists.....Daytonadan had some ideas that have merit....The first thing I would check is spark....Just install the new coil if you have it....BTW, welcome to the forum at iboats & Merry Christmas!....Cheers......JK

 

[wills-ggl]

Re: Cobra Runs Well, but eventually stops and wont start

Thanks,<br /><br />I have installed the new coil, and it still did it, so must be something related to fuel???? <br /><br />I will double check the spark. I spose it could be bad plugs and leads, failing at temp.<br />The only difference it that the engine cowl it shut when the engine is on the river, acting like a good convection oven.

 

[Don S]

Re: Cobra Runs Well, but eventually stops and wont start

Here are some items to check in the fuel system. I just copied them from a Volvo service manual.<br />Do you have a way of putting a vacuum gauge with a tee and a piece of clear hose between the fuel pump and the fuel tank?<br />Do you have a fuel pump pressure gauge you can tee into the system WITHOUT cutting any steel lines?<br /><br />1. Fuel gauge operation and wiring<br />2. Fuel level in tank<br />3. Water or debris in fuel<br />4. Fuel pickup tube and screen blockage<br />5. Fuel tank vent blockage<br />6. Plugged external canister or carburetor fuel filters<br />7. Air leak on suction side of fuel system<br />8. Fuel leak on pressure side of fuel system<br />9. Inoperative, restricted or incorrectly sized anti-siphon valve<br />10. Boat fuel lines too small in diameter<br />11. Fuel pump pressure and suction<br />12. Carburetor cleanliness and operation

 

[wills-ggl]

Re: Cobra Runs Well, but eventually stops and wont start

I do have a engine vacuum guage, could i put this in place to test pressure and vacuum for the fuel lines????<br /><br />the fuel system is a hybrid of steel and rubber lines, i should be able to tap into it with out much trouble<br /><br />1). fuel level guage works well.<br />2). The fuel tank will not accept anymore fuel <br />3). This would the second tank of fuel since running winterising fuel conditioner through tank<br />4). Again the boat has ran for a hour<br />5). I thought this may be a issue, but with the cap off if i blow on the vent hose i can blow fuel back out the fill line.<br />6). Has new fuel filter for winterizing only two tanks old (ie about 3 months old)<br />7). No apparent air leak but something that will need to be checked out properly<br />8). No Fuel leaks<br />9). Dont have one<br />10). they are 1/4 inch internal diameter, i would think that it would hesitate if it doesnt get enough fuel at WOT it doesnt even think twice about reving out. <br />11). Will check<br />12). Have got new carburetor for winterizing,

 

[Olds Eddie]

Re: Cobra Runs Well, but eventually stops and wont start

Just a thought. This sounds so much like a coil problem that I have to ask was that a new coil or a used one you came up with? Sometimes us pack rats forget to properly dispose of questionable parts and they find their way back onto an engine.

 

[wills-ggl]

Re: Cobra Runs Well, but eventually stops and wont start

The coil is a completely new coil, as you suggest it seemed som much like a dead coil that i did eventualy in my test change it but i got a negative response. Dropped the boat in the river and it still did it. <br /><br />It may just be electrical most likely something saftey related but im not sure. <br /><br /><br />Hey just a quick Q , is the switch that arms the do not start in gear saftey mechanim interfeer with ignition.<br /><br />Also BTW for the test the esa is off and out of the equation. but it works. <br /><br /><br />Thanks,<br /><br />Will

 

[DHPMARINE]

Re: Cobra Runs Well, but eventually stops and wont start

Do not start in gear switch does not affect the ignition system.We should rename it the Do Not Crank Switch.It keeps the starter from cranking.I was also thinking coil,but you've replaced that.<br /><br />Can you run the motor wide open and at what rpm ?<br /><br />I doubt it's a fuel problem because you are running @ 2500 rpm,then slow down and it quits,then won't restart.<br /><br />Can you tell us more ?Not about what you've tested,but how it acts up ?<br /><br />DHP

 

[wills-ggl]

Re: Cobra Runs Well, but eventually stops and wont start

Run motor crusing at 2500-3000rpm for a hour then engine stops.<br /><br />will crank but not start. for some time.<br /><br />at WOT the engine will rev out to 4500rpm easily<br />but not not go above that but according to the OMC workshop manual that is what should happen.

 

[Olds Eddie]

Re: Cobra Runs Well, but eventually stops and wont start

At this point I would suspect vapor-lock as the culpret. The fuel in the line may be boiling after a hot soak. (Turning off ign after running) You can check for this with a fuel pressure gauge between pump and carb. Good luck!

 

[Olds Eddie]

Re: Cobra Runs Well, but eventually stops and wont start

You can also squirt a little fuel down the air horn when it dosen't want to start as vapor lock is fuel arriving at carb in gaseous form as opposed to liquid. If it fires up you know what the problem is. The fix may be to re-route the line away from heat source or putting an insulating gasket under carb.

 

[markvictor]

Re: Cobra Runs Well, but eventually stops and wont start

You can also run your bilge blower,continuously at lower rpms when hot, to reduce engine box temp and vapor-lock

 

[wills-ggl]

Re: Cobra Runs Well, but eventually stops and wont start

yep yep,<br /><br />well long story short,<br /><br />I took the boat out and put 15 hours on it over 4 1/2 days . without a hitch, pulled the boat out of the water and then it wouldnt start.<br /><br />Worked out to be the contact set for the dizzy was earthing out, and was missing a washer. The contact set was replaced 2 months ago, so im hoping to move to a electronic dizzy.<br /><br />I feel that this was also the reason my coil was very hot to touch, and prolly why after some time it dies out. fixed now but i want to move to electronic ASAP.