johnt365

I have a wideband and "think" I know where my issue is. My car is a 350 with automatic comp xe268h Holley 80457 .

Idle - 13.5:1
Off idle to 2k - 14.7-16.5 There is no popping or anything, just that I see it go lean.
2k+ -13.5:1
WOT - 12.7-13.1

I am happy with everything but just off idle which I believe is the transition slot and controled by the Idle Feed Restrictors and Idle Air Bleeds. However, this model metering block does not have adjustable IFR or air bleeds.

I think I need to richen the transition a tad and to do this either make the fuel feed larger or the air bleed smaller. Is that right?

What are my options here? I see that QuickFuel sells metering blocks that look adjustable for $50 or so. Is this the best route or is there a way to convert the old metering block to accept adjustable IFR and air bleeds?

Crepitus

this thread has a couple of well labled pics;

http://forums.corvetteforum.com/c3-t...roperly-4.html

johnt365

That is a great thread. I don't have adjustable air bleeds in the main body of the carb. The IFR (B6) is also a fixed jet. Are my options to get a precision drill bit set and a pin vice and slowly enlarge B6 in order to richen the transition circuit?


Can anybody recommend a drill bit set that has a good range for carburetor work?

Or I could try something like this little guy

This is one from Quickfuel and has removable Idle fuel restrictors and power valve restrictors.

Matt Gruber

the only problem i see is that it is too rich above 2k cruise.
idle to 2k looks fine to me. u are very lucky. don't drill it.

johnt365

Matt,
Should I be worrying about an over lean mix in this range. I drove it last night and at 80 mph in OD turning about 2200 rpm it was around 13.7-14.2 .

My worry is that stop light to stop light the transition circuit alone can peg lean sometimes. I should try to take a video or something. If I accelerate any its fine. The lean is just off idle but no surging or bog (accelerator pump helps).

Matt Gruber

stop light to stop light it can peg lean? But if u accelerate it is fine? Makes no sense to me. Do u mean it has a flat spot where it does not accelerate, and it pegs lean?
Usually going way lean, above 17:1 is caused by pressing on the pedal and the vacuum secondary opens too fast, or there is not enough pump shot.

johnt365

let me go make a video now so we don't have to deal with my memory. be right back.

Matt Gruber

i won't be able to view it. maybe others will chime in.

chevymans 77

Johnt365;

The lean spike is more than likely caused by a transition/idle circuit that is not sensitive enough to throttle changes at that low an rpm (air flow).

I had that same issue with a carb I was tuning, the main air bleeds were in the .032" area and with throttle changes the AFR would spike to 20:1. I was able to reduce the main air bleed to .024" like the old Holley's and the lean spike was gone. To maintain the same AFR when on the primary jets I had to reduce the main jets along with the main air bleed, they work together to determine the AFR.

I would try inserting a small piece of wire in the idle air bleeds, bend it so that the air cleaner holds it in place. Try using a single strand of wire form a #14 multi strand automotive wire, the single strand is in the .007" range. Insert a strand into both the primary idle air bleeds and take a ride and see what effect this has. It should richen the idle/transition circuits below 2500rpms and make the circuit more sensitive to throttle changes.

Post back and let us know what you find.

Neal

johnt365

Thank you for the advice.

Even though I spent most of yesterday making adjustments. I went out and turned the idle screws just a hair richer. Now average idle in park is 13:1. I think this helped. There is no lean spike or performance issue, just me worrying this gauge.

The leanest it gets is if I hold a load on it at 1600rpm it will bounce between 14.2 and 15.2 hoovering around 14.6:1. There are still little moments of rich or lean at different times of deceleration or acceleration at different speeds that only a gauge can detect.

I think I am done. I can live with a 13:1 idle. I still plan to make a video but need to wait till dusk to do so because of glare.

Its hard to watch the tach, a/f, speed AND the road.

Crepitus

I had to look up the ifr on a metering plate. They are at the top towards the outside. The main restrictions are at the bottom. To drill you need wire drills. The good news is they are cheep to replace. A strand of wire in the ifr is common, no reason it wont work in the air bleed. Just make sure your engine cant eat it. You could swap in aftermarket metering blocks and tune to you harts content but you will be starting from scratch on all the metering restrictions. A possibility is swapping to an adjustable block on the secondary side only to keep. I did notice the Holley book shows some of the pri blocks have the ifr under a pressed in cap on top the block (out side plugs iirc)

Crepitus

Glad to see a happy Corvette! I like the idea of talkin you into drillin hackin and throwing stuff around the shop. It could be like your own little reality show! We could even throw in an online pissing contest

Matt Gruber

here is an example of proper cruise tuning:
.
mpg

454 in a 7000 lbs. 4x4
Lee's truck can now accelerate from 20 mph in 5th! The torque is back!
Quote lee_beazley
Sent: Sun Jan 27, 2013 9:02 pm
by lee_beazley
For now, I now have the 4777 and newly filled air gap[cut down divider filled in] running so well, I'm going to follow that up. It'll be good to have something to compare to anyway.
.
It's astounding what that little filler did. The mpg might still be less than I had hoped for, up to about 10 mpg ave[was 5-6 before], still not bad for a 7000lb 4X4, but this is fun and interesting. I have the idle leaned to about 14:1 AFR on the guage. It's not the smoothest idle[set lean to save gas] but it's still good, at 750 rpm. Starts with the touch of the key. The smoothest idle is rich, 13.0:1. The secondary plate is almost closed and there is very little slot expposed at idle. No hesitation though.
I went down two more primary jets to 63. The AFR, cruise at 55 to 65 mph, is now 14:5 and very steady. At 65 to 75 it leans to about 15:1.
.
It runs great. Fast warm ups, no hesitation, I even went through the roundabout getting on the freeway, this morning, at 20 mph, with a cup of coffee in hand, and just smootly accelerated down the on ramp to 65 in 5th gear. Unreal. Thank you again. lee

*