Subject: Not diy_efi....how to disable a computer carb

[Shannen Durphey]

neilaura at accessworldnet.com wrote:
> 
> At 03:26 PM 6/14/99 -0500, you wrote:
> >I would still check the M/C solenoid. The solenoid controls the primary
> >metering rods buy moving them up and down at a duty cycle
> >controlled by the ECM and its inputs. My 82 T/A did the same thing your olds
> >is doing , running extremely rich. The Q-Jet runs rich because a spring on
> >the metering rods pulls them completely out of the primary jets. The M/C
> >solenoid when energized pushes the rods down into the jets leaning out the
> >mixture. The only way to bypass the M/C solenoid is to convert back to the
> >vac type metering rods if this is possible . Fix the carb or go to a non
> >electronic Q-Jet and non computer HEI, of course the ECM now has nothing to
> >do.
> >Don
> 
> That's only part of it Don.
> When the solenoid pulls the needles down and closes off the jets it, also
> opens an air bleed valve to further lean out the mixture.
> Possible options are. Physically hold the needles half way in/out of the
> jets.  Or use a 555 as a base for a generating a 50% square wave, and
> disconnect the engine check light.
> 
> Neil
Been there, done that.   Physically balancing the two works great at
idle, but lousy on the road.  There's no deceleration enleanment, no
richening of mixture under load.  I suspect the reason the carb goes
to full rich is to give some semblance of driveability, especially in
the underpowered, highway geared barges they were first used on.  I've
run these carbs with the m/c solenoid disconnected, leaning the rich
stop some.  Don't hope to pass an emissions test though, especially if
it requires off idle testing.  Also, make sure the AIR pump isn't
pumping O2 into the manifolds or cat when you're running rich, else
you'll end up with a nice warm glow from the exhaust system.  Feedback
carbs take some real skill, IMO, and the time you invest in them could
easily be replaced with time in a junkyard pulling parts for a tbi
swap.  Bruce P can tell ya stories about those carbs, I've just
started working on them in the last few years.
Shannen