Need help fine tuning Refurbed '77 CIS

[rwest]

Hello,

I just went through my complete CIS; mainly for vacuum leaks. Car actually ran pretty good before, but I knew the air box had blown many times and I suspected unmetered air and wanted to get it running as close to new as reasonably possible.

I replaced all the seals, hoses, injector sleeves, air box and tested many of the parts either before or during the rebuild. I got it back in the car today and it started right up.

I had followed the factory explanation of turning the 3mm screw on the FD ccw a couple of turns, pulling all the injectors, purge the system and then turn the screw until the injectors barely sprayed, then backing off the screw half a turn.

The idle seems lower and if I let of the throttle, I get light backfiring out of the intake. I'm guessing that I'm lean, Do I need to turn the screw clockwise a smudge? 1/8 of a turn or so?

Thanks,
Rutager

[fanaudical]

Do you have the gauge for checking fuel and control pressures? If so, I recommend starting there and validating that cold and warm control pressures are within spec for your specific WUR. Following that, then you can set your idle mixture (preferably with an exhaust gas analyzer / CO meter if you have access to one). If you don't, please look at this thread:

CIS Idle Speed and Mixture Setting Without an Analyzer

[rwest]

Thanks for the link, I had read that, but was confused a bit by the explanation of the idle screw and the screw on the FD.

What are the relationships between the two?

I have the gauges, but I did test the pressures before I took it apart to see if I needed to address them during my refurb, I don't have the numbers handy, but I had verified them with spec and they were correct, so I'm figuring that it's a mixture issue since that is what I changed on the FD and by removing, hopefully any vacuum leaks.

[ossiblue]

Originally Posted by rwest

Thanks for the link, I had read that, but was confused a bit by the explanation of the idle screw and the screw on the FD.

What are the relationships between the two?

I have the gauges, but I did test the pressures before I took it apart to see if I needed to address them during my refurb, I don't have the numbers handy, but I had verified them with spec and they were correct, so I'm figuring that it's a mixture issue since that is what I changed on the FD and by removing, hopefully any vacuum leaks.

In the link, the idle adjustment screw is the screw on the FD, and the large slotted screw on the throttle body is the air bypass screw. Both need to be adjusted to set idle correctly as one, the idle adjustment screw, affects fuel flow when the metering plate is at a fixed height (adjusting the screw does not change the height of the metering plate on the plunger), and the other, air bypass screw, affects air flow which changes the volume of air into the engine and changes the height of the metering plate.

From the link: "This brings us to idle speed and how to lower it. If you paid attention, you’ll know that you can raise or lower you idle speed by changing both the bypass screw setting AND the idle mixture. You have to adjust both, not just one. You can adjust one at a time, and you may find that you will create a lean or rich surge. (That is actually the way you should do it if you are not confident of what you are doing) If you are closing the bypass, and the engine surges, then reduce the fuel. Get the idea? Air and fuel combine to produce energy when ignited. Often a high idle speed is the complaint. So reduce air and fuel to reduce the idle speed. Be wary that you do not have a problem somewhere else which is causing your high idle. " (Emphasis, mine.)

[rwest]

L.J.,

Thanks for the clarification, I did some fine tuning of both and it appears like I have got them set for good idle and running. I need to put a few things back on the car before I do a test run. I'll report back on my results.

Rutager