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4.3's Both engines running rich and starboard engine bogs at 3600

cyborg

New member
Both engines running rich and starboard engine bogs at 3600
Boat is a 1959 35ft Chris Craft.
Trying to establish WOT RPM in order to make proper pitch selection.
Current props seem to have approximately 2 inches too much pitch and are cupped
When trying to achieve WOT, the port engine will rev to 3900-4000 and seems fine
The Starboard engine will go to 3600 and then bog ( feels like it‘s cutting out). RPM’s will drop to around 3000
Pull back on the throttle and the engine will catch and smooth out
Move the throttle forward and it will increase to 3600 and bog again
When it bogs, there is a very loud resonance coming back through the spark arrester.
You can repeat this process and it is consistently bogs at 3600
When throttling up with just the starboard engine, the bogging starts around 2500
Same situation: noise through arrester, pull back throttle and it catches
Seems like bog is more sensitive to throttle position than RPM?
No noticeable change in vacuum when bogging starts
Plugs come out black on both engines.


Twin 4.3 Mercruiser LX Gen+ 2BBL
I/O engines converted to inboard.
Installed carb wedges to compensate for engine angle.
New exhaust manifolds, 4” tubes and flappers.
No mufflers , so don’t think there is a back pressure problem
Engines rebuilt with new pistons, valves etc.
165-170 lbs compression on all 6 cylinders
New fuel tanks, lines, filters, vent is clear
4.5 lbs fuel pressure at WOT
9 degrees base timing and advance is working
No sign of balancer slipping
#1 cylinder both valves closed when balancer is at TDC
Swapped ignition module and sensor assembly from good motor
Replaced plug wires, rotor, cap, coil wire, and coil.
Disconnected house battery, bypassed battery isolator.
Clean grounds running on fully charged start battery @ 14+ volts
Disconnected tach wire
Starboard Mercarb replaced with professionally rebuilt, bench tested Rochester
Port carb (Mercarb) has updated float needle and seat.
Spark arrester is clean and was swapped from good engine.
Tried running without spark arrestor
Engine temp is steady at 160
Plugs are new gapped at .045
Engine vacuum within spec.
So the questions are: 1. Why is the starboard engine bogging and resonating back through the spark arrestor? 2. Why are both engines running rich and they seem to run consistently rich from idle to WOT?
I’m starting to grasp at straws….. Wondering if it has something to do with the carb wedges. I like to think that I’m not dumb enough to beaver up the cam timing on both engines. Any suggestions would be appreciated
 
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