gruveb

.......

and I'm really ready to screw this thing up.

Check my sig for the modifcations.

The carb is a 600 cfm edelbrock electric choke carb. The air/fuel gauge shows that at cruising speeds and idle I'm running slightly rich (2 or 3 LED's into the rich side), under a consistent load I'm running slightly lean. I'll have to double check how lean it is, I've only drive it this morning with the air/fuel ratio gauge working.

Any input?

Apeiron

Assuming the gauge is working correctly and accurate, you could use a rod with a larger cruise step to lean out the cruise mixture, and put in a heavier step-up spring to richen the mixture sooner under load.

gruveb

That brings up another question I had. How to do I tell if the gauge is accurate?

I assume that the signal from the O2 sensor is a ground..... but that doesn't help me out much.

It is an auto meter gauge, so it's not a cheapie sunpro or anything, but regardless.

F-BIRD'88

The idle AFR is near right. It should be a little richer
than the middle (14.7:1) it will be around 13.0:1+/-.

Low load cruiseing is ok to be a little lean.(er) than 14.7:1)
Saves gas. As long as the motor does not surge, detonate
or show signs of overheating) (15/16:1 approx.)
The guage should go rich ( 12.5/13.0) when ya get into the throttle.
A guage like that is only really accurate at 14.7:1 but it will indicate richer than or leaner than and help in tuning.
Use the guage in combination with the appearance of the plugs, driveability and common sense.
The O2 sensor must be hot to work and there must be no exhaust leaks ahead of it. ( like headers etc).



Read and know this stuff

gruveb

Thanks.

Actually I'm rich at idle and light load and lean under heavy load.

Almost backwards huh? I haven't really even tried to tune the carb yet even with the vac gauge as I have literally just got it all back together. I have the timing set at 8* initially but it feels like I woudl benefit from a little more.

There aren't any exhaust leaks before (or after) the O2 sensor.

So should I use a rod with a larger cruise step to lean out the cruise mixture, and put in a heavier step-up spring to richen the mixture sooner under load like Aerpion suggested?

F-BIRD'88

You have to up the main jet to change the full throttle "jetting."
Actual you have to select a jet rod combo that will give you the effect.
Read the tuning info and use the tuning charts (Edelbrock) to select the right
rod and jet combination. The power spring adjusts the load timing point where the rod shifts from down in the jet (lean cruise) to up (power mode)
The idle feed restriction (non adjust able) may be too rich
for your use. How rich does the guage indicate?

Try leaning the cruise mode (rod) and richening the power mode)
and go up 1 stage on the sec jetting.
The rods must remain down in the jet at idle.
The PCV valve must be hooked up and the other valve cover be vented.
Set the timing with a advance timing light for full mechanical
advance of 32 to 36 deg at high rpm (4000+). with no vacuum advance. then reattach the vacuum advance.

gruveb

Only slightly rich.




I wish I had one! That's next on the shopping list!

Thanks for pointing me in the right direction. If there is anything else you can think of, please let me know. Time to get into my manuals and start learning a little hands on huh?

F-BIRD'88

"Only slightly rich" is ok. Actually just right. It's usually real close on these carbs.

gruveb

But I'm definitely LEAN under load. Initially lean is one thing, but under constant load, very lean.

F-BIRD'88

You're talking about full WOT acceleration right?
Hummm.. I'd check the fuel flow (pump. lines, tank pickup, filter) and float level.
Shouldn't be that lean at full WOT throttle.
Then start upping the sec jetting.
If it only goes lean for a split second as you roll into the throttle but then goes towards rich as the motor accelerates
then it is the accelerator pump shooter size
not the jetting.
Pull the top off the carb to ensure it has the right base jetting to start with and proper float setting.
Something is up cause it should not be severly lean @ WOT out of the box ...

gruveb

Well, I haven't really had an opportunity to have it at WOT for more than a sec or two, so I'm not sure about WOT.

I do need a new fuel pump anyway, but there are only so many things you can do at once, you know. Either way, it's not effecting me at anything less than WOT. I have only 4 to 5 psi fuel pressure, so it's suspect.

F-BIRD'88

5 Psi is ok as long as the pump can maintain that pressure
at high fuel flow. WOT high rpm.

gruveb

That is the part that is suspect. Just from the way the car behaves at certain times makes me suspect the fuel pump is weak.

I'll be changing it soon. It's almost 20 years old anyway.

gruveb

At freeway cruising speeds there are times where it goes extremely lean for 30 to 45 seconds at a time. It's not all that uncommon either.

Would that be a problem with lack caused by lack of fuel?

F-BIRD'88

could be.