phil chieco
Cadet
- Joined
- May 5, 2012
- Messages
- 21
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 water in oil. Wonder if my timing could have been thrown off. Now running 91 octane ethanol free which stopped the dieseling. Purchased an advanced timing light set it at 10 degrees and followed mercruiser instructions. Hand no luck timing it as it made backfiring worse when I aligned the harmonic balancer mark with the one mark on bell housing. Ended up adjusting distributer by ear at idle which eliminated backfiring but still runs a little rough at 1000 to 1300 rpm. Air idle screw is out at least 4 turns and when I turn it in the idle gets worse. Tried initial setting at 1 and 1 /2 turns out and was very rough. Also put the engine in base timing mode with all settings. Wondering if the hydrolock screwed with the harmonic balancer line . Any assistance would be appreciated.. maybe another carb rebuild?
There was no water in oil. Wonder if my timing could have been thrown off. Now running 91 octane ethanol free which stopped the dieseling. Purchased an advanced timing light set it at 10 degrees and followed mercruiser instructions. Hand no luck timing it as it made backfiring worse when I aligned the harmonic balancer mark with the one mark on bell housing. Ended up adjusting distributer by ear at idle which eliminated backfiring but still runs a little rough at 1000 to 1300 rpm. Air idle screw is out at least 4 turns and when I turn it in the idle gets worse. Tried initial setting at 1 and 1 /2 turns out and was very rough. Also put the engine in base timing mode with all settings. Wondering if the hydrolock screwed with the harmonic balancer line . Any assistance would be appreciated.. maybe another carb rebuild?
