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Old 08-02-2017, 01:11 PM
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Join Date: Jun 2016
Posts: 4
Default Mercruiser 5.0L dies when throttled to high speed

My 1998 5.0L Mercruiser Alpha 1 V8, upgraded to the Surestart system, faltered after being underway at about 18-21 mph for about 20 minutes and died.

Restarted easily, got underway, and again faltered and stopped. Not an abrubt stop but a maybe a 5 to 8 second power down when the throttle was advanced.

Restarted and idled to a mooring field about 1-2 miles away and got towed back to the launching ramp.

I was able to duplicate the faltering and quitting at advanced throttle back home on the trailer.

What I've determined so far:

NO water in the fuel. Poured the contents of the water separating filter into a clear bowl and it was all gas. Gas and carb filter were clean.

Ran a fuel pump test and it pumped a healthy stream of fuel into a bottle. Fuel was both new high octane, pumped in on the way to launch and treated last years fuel. It work well in my pressure washer.

Distributor cap had slight pitting on contacts which I cleaned off.

Haven't looked at the carburator jets.

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Old 08-28-2017, 12:24 PM
Junior Member
Join Date: Jun 2016
Posts: 4
Default Solved!

Thanks to the 'car guys' on public radio, the problem is solved!. A caller had the same symptoms as I did, except on his BMW 2002. He went through the list of possible causes to no avail (saving me $300 just on not replacing the fuel pump). Click and Clack knew immediately it was his carburetor jets.

And sure enough, that was my problem. I removed the top half of the carburetor where the jets lived, removed them and blew air through every opening and passage and found them all clear except possibly for one which I may have blown clear, not sure. The float and valve was also working properly.

What I did find was a small amount of gummy residue on the bottom of the accelerator pump chamber which I cleaned out. It didn't seem to be interfering with anything but I now have what seems like a brand new boat. It idled through the mooring field in Falmouth, Maine (800 boats?)without missing a beat and ran all the way home, 3 nautical miles, at a steady 30mph. Engine response to the throttle was perfect.

Cost: $50 for a gasket set.

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