87 Larsen OMC Cobra 4.3L I/O Stalls under Load

TJBC

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Joined
Jul 25, 2014
Messages
4
Little Frustrated and running out of options
87 OMC Cobra 4.3 idles and runs great in the water; engage in gear and you have about 2-3 minute before it bogs down and quits. Almost impossible to get started for about 2-3 hrs, but them starts and runs fine (like nothing ever happened). If you do get it started right after it quits, it runs really rough and will not idle. The engine block is actually a '96 so we had to put an electric fuel pump on it.

Here is what I have done:
Rebuilt the carb 3 times - twice by myself and the last time by a professional
Checked the tank vent & check valve
New filters and Fuel Pump
Tested the fuel pressure line right before it goes into the carb and I have 2 - 3 lbs. even as it is dying.
I can see the spray in the carb from the accelerator pump when it first throttles up and the fuel 'misting' out into the two barrels while it runs.
Unhooked the line from the tank and just had the fuel pump suck out of a small gas can (91 octane Ethanol Free)
Test the coil right after it has died and the voltage is all the same as when it was running ( at least, key on/off, and cranking)
I have just about ruled out a fuel problem, so wondering if maybe I am only getting 'weak' spark after a couple of minutes. I can hear the ESA retard the engine when I put it in gear, but then I runs good for about 2-3 min. until it dies. Any suggestions? Can my points and condenser cause an issue like this? Any other electrical issues I am not thinking about? I appreciate any thoughts.
 

Bondo

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Apr 17, 2002
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70,470
Ayuh,.... Welcome Aboard,.... Durin' this 2 or 3 hours, have ya Checked for Spark, 'n Gas while yer waitin',..??
 

TJBC

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Joined
Jul 25, 2014
Messages
4
Thanks for your reply. While at home hooked up to the muffs, we tested the voltage on the coil so that we would know what it was supposed to be so we could test it again when the boat died. Here is what we came up with:
Neg Positive
Ignition Off 0 0
Ignition On 0 4.5 - 5
While Cranking 4 - 4.5 9 - 9.5
While Running 6 - 6.5 9 - 9.5

The next time we went out on the lake the boat died. We got these exact readings on the coil 20 minutes after the boat died (had to paddle back to the dock). I also took the spark plug out and checked for spark while cranking. Can definitely see a blue spark. My hand got a little close to the plug and it shocked me good to.
The fuel pressure gauge, that I have mounted in the fuel line just before the carb, would automatically go to approx. 3 lbs. when the key was turned on (fuel pump was running). I also lifted the top of the carb and could hear the fuel go into the bowl as I raised it up (float came down). I put the top back on the carb and manually pushed the throttle forward and could see the spray in the barrels from the accelerator pump. Pumped it 3 times and cranked the engine. It fired and ran for 2 sec and quit; even manually continuing to pump the throttle. Would not idle.
However, if you wait till the next morning the boat will start and idle just fine like nothing was ever wrong. As soon as you get in the lake and put it under a load, it bogs down and dies in about 2 - 3 minutes. Then back to square one ???
 

TJBC

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Joined
Jul 25, 2014
Messages
4
Sorry about the coil readings. When it posted it changed my formatting.

Negative Side (-) Ignition Off - 0, Ignition On - 0, While Cranking 4 - 4.5, While Running 6 -6.5
Positive Side (+) Ignition Off - 0, Ignition On 4.5 - 5, While Cranking 9 - 9.5, While Running 9 - 9.5

Thanks.
 

TJBC

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Joined
Jul 25, 2014
Messages
4
I decided that I would start back at the beginning and look for any other possible problems. So here is what we did:
- Drained all the fuel out of the fuel tank and cleaned it really well. As we were draining the fuel out of the tank we noticed air bubbles in the fuel line. After removing the tank we noticed the fitting going down into the tank was really loose and allowing air into the fuel line. We replaced the line and used new compression fittings.
- Put a new fuel pump (2.5 lbs. - 5 lbs.) and new filters all the way through.
- After much debate about the carburetor, we decided to have one more professional opinion. Took it to another mechanic who went through it. He changed the filter, replaced the power valve, cleaned it, and reset the mixture screws.
- We also had the points and condenser replaced.
Took it to the lake and it ran like a champ. Not exactly sure what the problem was. Just happy that it seems to be fixed now.
 
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