Fluctuating idle 2001 5.7 alpha one 2bbl carb

[outobie]

Been having some idling issues recently idle fluctuates between 450 and 900 on its own

Has thunderbolt V ignition

to address I've done the following:
all oem mercruiser parts

new alternator
New fuel pump and filters
new spark plugs
new ignition trigger
new cap and rotor
new carburetor
new thermostat
new pcv

while grounded in base timing mode
checked timing with strobe ... perfect at 10 degrees
carefully tuned carb per factory manual
confirmed throttle and shift linkage and interrupt switch are set to factory spec

engine idled perfectly at 650 rpm @ 165 degrees in neutral at the dock while in base timing mode.

once I disconnect the base timing mode grounding wire
idle rpm fluctuates while maneuvering around docks

sometimes it stalls and sometimes it revs so high it bangs the gears when shifting

where do I go next?

motor otherwise runs perfect sounds good makes great power and is a joy to run doesn't burn oil doesn't smoke or make any noise it shouldn't

 

[outobie]

Bump....

 

[fastjeff]

IF you had a four barrel carb, I'd say the secondaries aren't closing tight every time, but...

Is the throttle cable pushing the carb TIGHTLY closed? I had to add a turn or two to mine.

Jeff

 

[outobie]

Thank you for the suggestion

yes throttle closes hard against the stops

i visually confirmed butterflies are fully closed for the last few degrees of movement at the throttle

given that the fluctuating only occurred when timing is not grounded into its base timing mode I was thinking it's an issue with the electronic timing modules but don't know how to test

 

[fastjeff]

Agreed. Don't know what to do about it except do some parts changing.

Jeff