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Old 12-11-2011, 01:45 AM   #1
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Default Port Engine Headaches with 05 2900SC twin 4.3L (2bbl carb)

This year I spend more time in engine compartment then enjoying sunny days on the water and here is the whole story…
I got myself beautiful 2005 Maxum 2900sc with only 120hrs on engines and before I got a chance to take it out for a decent ride and waiting on the dock for engine to worm up temperature alarm started beeping. Jumped right in and turn off port engine before it got overheated. That was easy fix replacing impeller row water pump 3hrs job and couple bears was not big of a deal.
Another problem was with backfire through carb, noticed bad wire from coil (I was starting engine in complete darkness and you can see sparks jumping).
Not a problem again new wires, distributor cap, rotor and spark plugs, which is what you suppose to do, right?
Improvement on engine performance was just a bit better but port engine still backfires through carburetor. Next on the list was to check carburetor and I found out that in one barrel fuel is dripping while other one sprays nice mist.
Got myself carb rebuilding kit, and that was not too hard to do.
Carburetor works fine nice mist in both barrels but still backfiring.
To eliminate possibility of bad carb I even swapped carb from good engine and still no improvements port engine backfire.
Possibility of bad fuel, vapor lock and dirty fuel filter where one of the first things I eliminated.
Just to be on the safe side I replaced coil also and gas tank was filled up with shell premium fuel with no ethanol plus star-tron was added as I do every time.
At this point main suspects are valves so I’m doing compression test and I found nothing wrong very close to 190psi on all 6 cylinders and same reading on the good starboard engine.
Finally decided to get help from local old school mechanic checked timing (no issue there) and overall he really couldn’t find problem.
Now this is what is happening when I’m on the water:
If I don’t “baby port engine throttle” it will backfire any bigger move with throttle will backfire and stall.
I’m getting only 50% power of port side engine
To get on the plane takes long time and to cruse both engines at full throttle (since starboard do all the work)
Maximum speed I got was 28mph beautiful day ideal condition
Port engine only following starboard doing 200-300 less rpm and any throttle backing up with good starboard engine and port engine rpm will drops also.
Occasionally port engine will keep going and dieseling after ignition key was turned off.
I would appreciate any thoughts since I truly like to enjoy next season.
Thanks
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Old 12-11-2011, 02:30 AM   #2
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Is it running hot?
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Old 12-11-2011, 03:42 AM   #3
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flamies in the carborator is always timing.

mechincal timming weights, and/or vaccum advance in the distributior are stuck.

Replace the distributior or the electronic timming advance, which ever that engine has.

Could be as simple as the grease fitting on the distributer.

Book says something about a "timing advance system jumper wire from the 3 point connector", and the bypass shift interrupt switch ---DO NOT FORGET TO RECONNECT THESE TWO WIRES"
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Old 12-11-2011, 08:54 PM   #4
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Thanks Pascavone,

What you saying make sense and I’m willing to give a tray.
Could you be more specific what book are you referring to…?
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Old 12-12-2011, 01:54 AM   #5
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www.selocmarine.com

mercruiser stern drives 1992-01 repair manual, covers all gasoline engines. includes alpha, bravo, blackhawk and all inboard transmissions.
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