Tuning help

I just finished installing an AEM wideband guage in the car which uses a Bosch LSU4.9 UEGO sensor. I went for a drive and once at full operating temp I began watching the guage. At a 45 to 50 mph cruise I was seeing readings from 14.4 to 14.9 which seems pretty good...considering I have 75 main jets currently. But when I slow down to about 35 mph it gets a bit fat with readings between 13.5 and 13.8 approx. I'm not sure what this is telling me...do I need to lean the main jets or leave them?

Gene, screw the idle mixture screws at idle on the lean edge. If still rich in the transition mode if you have screw in idle jets drop from say .034 to .032. That will lean out that mixture just cruising around the neighborhood. 13.9-14.1 area is fine.
Make sure you reset the idle mixture first after an idle jet change.
What kind of metering block do you have??

I have that aluminum aftermarket metering block with the adjustable pvcr restrictors.

What size jet is in the idle circuit??

Shoot I never wrote that one down so no idea until I take it apart. So why do I want to lean the mixture? isn't 14.2 to 14.7 ideal cruise a/f? Just to be clear...the higher the value the leaner the mixture...correct?

High cruise mixture is dependent on the main jet size.
Cruising around the neighborhood @ 15-20 mph is the transaction A/F which is controlled by setting the idle A/F mixture on the lean edge & or the size of the idle jet. 14-14.4 is fine if you have no hesitation on slight acceleration.
If you have a 13.5 then a leaner idle jet would get you closer to the 14 range or slightly above.
Remember most Holley's & Quick Fuel's metering blocks are jetted for a V-8.
Let your A/F wideband be your guide.

Hey Bill...just to refresh my memory...the idle restrictors are the two at the top of the metering block...one on each side...correct? In the middle of the block are the emulsion restrictions. I found my notes from years ago when you helped me set this up...looks like I have .032 in the idle feed restrictions now. All of these restrictors take the same 6-32 bleeds correct? Should I try .030 in the idle restrictions then?

Gene, you are not that far off. You could try .031". With your engine i would not go with .030"
Yes they are the two ones close to the top.
I have been in contact with many of the top dogs on the position of the idle jet & all of them place then at the bottom just like the stock Holley position which places them below the float level.
The reason for this is an engine with especially a non stock camshaft creates a pulsing condition on the idle jet when located at the outer top.
I have been relocating idle jet back to the stock position outside the PVCR passage. You have to be very careful when tapping the metering block, cause if you go too far the 1/8" 6-32 brass jet needs to be just level with the top of the passage. You don't want to tap too far otherwise it will bottom out in the lower idle passage.
My advice is just leave it at the top position with a .031" jet. However If you screw up the mod you can always go back to the top. You use a 1/8"-6/32 which is inserted with an allen wrench. You can't use the QFT ones that have a flange & use a screwdriver to install.
If you have a question PM me your phone # & i will give you more info. Bill

Yeah...I'm not going to tackle that modification. I'll just go ahead and install an .031 bleed in the existing locations and see how that does. Of course with all the 6-32 bleeds that I have...and I have many...I do not have an .031 so I will have to order from QF.

Bill...I sent you a pm.

Re-sent my pm.