Yet another wide band question

[charger1972]

I recently installed a wide band o2 to dial in what I thought was a rich idle . Turns out the idle is/was good but at cruise 2500 rpm reading 11 . Jetted down some got it to 12 / 12.3 ish . Should I keep at it or leave it where it is ? Engine is a 512 with an 850 with  mechanical secondaries , 76 in primary 85 in secondaries right now .

[A383Wing]

if you can get it to 13, that would be good....optimum is 14.2 all around....but unless you are running a computer with fuel injection, that won't happen. 

[BSB67]

I recently installed a wide band o2 to dial in what I thought was a rich idle . Turns out the idle is/was good but at cruise 2500 rpm reading 11 . Jetted down some got it to 12 / 12.3 ish . Should I keep at it or leave it where it is ? Engine is a 512 with an 850 with  mechanical secondaries , 76 in primary 85 in secondaries right now .

Use your tuning skills for your idle quality.  The 02 meter is a tool, not the answer.  Don't get too hung up on the idle numbers.  Remember what it is measuring.

For your still rich condition at 2500, I assume that you've checked the PV (personally, I've never found the PV to be the problem) check your float levels (unlikely the problem, but easy check), then try a wire in the IFR.  If the carb is a 4781,  76 jets are okay, but probably on the lower end of where I would go.  If the wire does not help off idle to 2500, then drop the jets a little more.  Watch your WOT readings.

[XH29N0G]

Some quick thoughts.

Make sure your PCV is doing what it should (if you are running one - I am).

If you are changing the main jets to fix the a/f at 2500 RPM, make sure you are into your main circuit at this RPM.  

I think you have four basic settings to mess with.

1. The main jets need to cover higher RPM as well.  You want to make sure you have the right a/f at higher RPM 3500, 4500, 5500.  and that it is relatively flat or slightly rising.  Something like 12.5 to 13.5 if I understand correctly.  That will be the main jets and main air bleeds.

2. The cruise will often still be the idle circuit and just with the transfer slots exposed so it is controlled primarily by the idle air bleed and the idle feed restrictor.  The wire in the IFR mentioned above will lean the cruise circuit and is described in many places.  I also put in screw in restrictors for mine, but found that the ones I bought had the wrong size holes (were marked one size, but were drilled another - I checked with some sewing needles to see how far they fit in.)

3. Idle covers the transfer slots and lets you modify the low speed air fuel with the idle mixture screws.  The settings will differ depending on the IAB (and IFR).  As previously said, tune these to what your engine likes (using a vacuum gauge - my car likes something like 13-14 on idle - yours may be slightly different).  You adjust this to fit the IFR and IAB.

4. The last is the accelerator pump.

I contacted a carburetor tech at quick fuel b/c that is what I am running and received good advice on adjustments.  I also looked through the internet to find several tuning guides that explained the circuits and tuning and think that helped me understand this too.  

I found it pretty easy to get myself in trouble so it was important for me to have good notes and only do a little at a time.  The process was enjoyable though and I learned a lot.

[charger1972]

Thanks for all the advise . The carb is basically a quick fuel / proform built by ccs . It has the site glasses and air bleeds so is very tunable . I will try some of the things you guys recommended and see what happens . I did start messing with the high speed air bleeds but , the results were not what I was looking for so put the old ones back in . I did change the idle air bleeds a while back to 70`s to get the idle to lean out . That was before the sensor was installed . Maybe need to go bigger ? Thanks again for the help .

[XH29N0G]

Maybe give that a try.  It is an easy swap (as long as you don't drop the bleed down the venturi) and you should see it on the a/f reading.  I think you will need to reset the idle mixture screws.  If you make a small change, set up the idle mixture to the same reading (I suspect that I can also see that in the cruise when I make big changes which I believe is because it is introduced through another passage in the throttle body).   

[charger1972]

Maybe give that a try.  It is an easy swap (as long as you don't drop the bleed down the venturi) and you should see it on the a/f reading.  I think you will need to reset the idle mixture screws.  If you make a small change, set up the idle mixture to the same reading (I suspect that I can also see that in the cruise when I make big changes which I believe is because it is introduced through another passage in the throttle body).   

So maybe 72`s ?

[XH29N0G]

I would ask someone who knows the setup and carburetor - maybe the people who put it together or quickfuel directly.  Mine have been changed by about 4 steps higher from what was OOB.  The first one was set up by the people who built the engine.  The second time was when I decided to try a different carb and set it up using the A/F as you are doing.  The first one was 74 instead of 70 and the second was 78 instead of 74. Both yielded cruise in the high 14's tipping into 15.  

The other option is to try the 72 and see if that helps or hurts.

[charger1972]

I think I`m gonna drive it tomorrow to work so ....  I`ll try the 72`s . 

[charger1972]

So , I messed up . The carb came with 75`s idle air bleeds and put 80`s in . I don`t have any bigger than that , so if I go that rout gonna have to order them .

[justcruisin]

As I read it you said your idle was OK but the cruise was rich. No point in messing with IAB's for RPM above 2500. I would come down on the mains and see how it looks. You need to be careful that you have enough fuel at the top end, if you come down to far you may need to increase the size of your PVR's. Check all settings first as previously said. The gauge is one tool out of a box of tools, plug inspections are still required - IMO.

[1974dodgecharger]

are you cruising truly as in same speed consistent when you are getting 11 to 1?  I get 12 to 13 on a cruise and hammer it I can dip down to 11:1, but I do that on purpose due to AZ heat out here helps cool my setup. 

Overall I think your, 'ok' , but 13:1 would be ideal for a carb engine just MO.

They say not to change too much at once on a carb...one thing at time and test.

[charger1972]

So , just want to say thanks to everyone for the help . Had it pretty close , but was lean under load . So jetted back up . But before I could dial it in , blew a head gasket . Then when it was all back together and ready to go , came down in the morning to drive it to work and no spark . So my MSD 6al is dead . I think `i`m gonna send it to be rebuilt .

[myk]

Is it an analog or digital model? 

[charger1972]

Analog . Pretty strange , just quit no warning . But , electronics will do that I guess .

[myk]

Analog . Pretty strange , just quit no warning . But , electronics will do that I guess .

Well I imagine it was pretty old.  Replacement?  Firecore?

[charger1972]

I have the Firecore wires and distributor . Will probably get a new MSD 6al digital box . Was gonna have the old one rebuilt but , I guess it`s a little out dated .

[myk]

I hear a lot of folks are having trouble with the MSD6 digital.  I would look for another analog box or run the Firecore ready to run distributor...