Mercruiser 4.3 stumbles at 1000 rpm and less

P

Phil Chieco

Member
Member
Joined
Jun 25, 2001
RO Number
5084
Messages
67
My 2002 carbureted 4.3 ThunderboltV double barrel has recently started to run fast and slow at low RPM. Under 1000 or less RPM just cruising along. Then when I accelerate it hessitates and sometimes backfires. Runs great at WOT. Replaced sparkplugs, checked gas tank breather hose all clear, cleaned oil pressure sender contact leads as I thought it was shutting down fuel pump. Carburetor rebuilt 7 years ago or 200 hours ago. Boat has 400 hours. Tried adjusting fuel air mixture screw did not make a difference. Also wanted to mention that I experienced a hydrolock condition two weeks back when the boat dieseled. Engine would not crank. Pulled plugs and manually cranked engine to get water out then ran starter to clear all water out.
There was no watrr in oil. Wonder if my timing could have been thrown off. Now running 91 octane ethanol free which stopped the dieseling. Looking for advice Thank You
 
You two are scaring the crap out of me! My two 4.3L's have the MerCarbs (2 bbl). They are 20 years old and have never been touched. They run great!
 
no worries then, keep using whatever gas you've been using and boat on!
Here in metro NY-Long Island we have no choice, e-10 gas is all they sell.
 
10% Ethanol is 99% of what my boat uses too. I guess I got the good ones! :)
 
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