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2007 4.3 2-Barrel Carb "Turn-Key Start" Mercruiser engine run-on or diesels

G

guyjg

Gold Medal Contributor
The engine runs great all day long. After a 1-2 mile long run on the lake to the dock I'll idle for ten minutes until loading it onto the trailer. I rev it to slide it onto the trailer and then shut it off before pulling the throttle to idle; that is when it sputters about 20-30 seconds. I installed new AC spark plugs per the manual last spring long before this started a few weeks ago. The plugs I removed had rounded electrodes but their color was brown on each one. I tried Marathon 93 octane with Berrymans fuel additive but it still happened. Do I need to de-carbon the engine? Any ideas fellas would be appreciated.
 
That problem--that plagued early emissions cars--was caused by lean fuel mixtures combined with advanced timing. Try adjusting the carb idle mixture screws richer.

Jeff
 
The 4.3 has an issue with dieseling to begin with... Shutting your engine down before pulling the throttle back to neutral is the cause of your issue. I would advise that you stop doing this. If the engine decides to pop off in reverse rotation when you shut it down, you will do lots of $$$ in damage.

This engine was designed to run on 87 octane.... You will have a power loss with 93.
 
Thank you all very much for the great information. I realized it might be the throttle not in neutral...just couldn't reach it quickly so I turned off the key.
What kind of tool is required to adjust the mixture? Do I need to install a nipple in the intake manifold for a vacuum gauge to adjust the mixture for near perfect adjustment? I did that on my last 4.3L w/Mercarb and it worked well.
 
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