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Holley Rich at Light Throttle

Posted By: 6bblFLASH

Holley Rich at Light Throttle - 06/10/12 11:59 PM

My 950 Holley runs too rich at light/cruise throttle.
Idle is 13.5 AFR
Light throttle 1,300---2,500 AFR is 10.9--11.5
Max throttle 12.5

I can get it lean at cruise 14.5 AFR by leaning out the idle and transfer feed passage,but then it won`t idle at 16.7 AFR.
Whatever I loose/gain at cruise takes idle with it.

IFR`s .040
AFR`s .070
Idle vacuum 7/8in.s
Light cruise 12/14in.s
Whats the trick to stop the idle/transfer circuit from keeping up with more vacuum?
Posted By: AndyF

Re: Holley Rich at Light Throttle - 06/11/12 12:12 AM

Light throttle should be on the main jets so lean them down and see if that solves it.
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle* UPDATE* - 06/11/12 12:17 AM

Quote:

Light throttle should be on the main jets so lean them down and see if that solves it.



Jetting has no effect on it till after 2,500 on the road. Tried several big jet changes 74/78/82/84. Had NO effect on light throttle/cruise AFR.
Car has stock converter and 3.55 gears so it rarely goes over 2,500 unless I`m "playing".

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Posted By: VanishPt

Re: Holley Rich at Light Throttle - 06/11/12 12:18 AM

I would look at the ifr's. .035 should lean it up a bit.
Posted By: YO7_A66

Re: Holley Rich at Light Throttle - 06/11/12 12:30 AM

IFR's below 2500rpms or so pending the size of the main air bleeds. The main air bleed slows up or speeds up when the mains start to come in.
IFR changes will produce the largest a/f changes per swap. I swapped from .028's to .031's which changed my cruise a/f readings by 1.5 to 2.0 with no other change. Then once you get your off idle and cruise a/f in the range that you like, then use your air bleeds to tweak in your smaller a/f changes. I made a change in idle air bleeds by .003 (x 4 bleeds) and found an a/f change at cruise by .4 to .6.
Hope this helps.
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle - 06/11/12 01:21 AM

Quote:

I would look at the ifr's. .035 should lean it up a bit.




Thats what it had,same results. After I leaned out the transfer circuit it needed more fuel at idle.
I will try smaller ones again if thats what you guys suggest.
Never tuned with an 02 sensor before. Boy these things are sensitive!!!
Old way was"runs good-close the hood"
Posted By: radar

Re: Holley Rich at Light Throttle - 06/11/12 01:49 AM

What worked for me is lean out (restrict) the IFRs until the idle corner screws are around 1.5 turns out. My 750dp jetted properly for wot only had the screws 3/4 turn out and was pig rich on the transfer slot. I don't have jettable ifrs so I have to use wire.
Posted By: RobX4406

Re: Holley Rich at Light Throttle - 06/11/12 02:20 AM

Have any .023-.025 welding wire?

Snip a couple pieces put in IFR, bend 90* and lay in channel, see if that helps. If it does, reduce the IFR to about .029-.031 range.

Main jetting likely will not solve this problem. BTDT! In fact after you get the cruise AFR's correct, you'll likely have to step up the PVCR size just a bit.
Posted By: YO7_A66

Re: Holley Rich at Light Throttle - 06/11/12 03:01 AM

""Thats what it had, same results. After I leaned out the transfer circuit it needed more fuel at idle.""

You will need to readjust the idle mixture screws once you change the IFR's. Readjust the IMS's so that you have the strongest vacuum in D (foot on brake or emergency brake applied) or if a manual tranny, in N.
Once you have the idle circuit back on track after swapping IFR's, then drive the car and see if you need to change the idle bleeds to compensate. If you swap the idle bleeds, make sure to readjust the IMS's again.

--------------------------------------------

""I can get it lean at cruise 14.5 AFR by leaning out the idle and transfer feed passage,but then it won`t idle at 16.7 AFR.""

This is proof that the IFR swap is what you need to get you into the 14's. Once your IMS's are readjusted, then you idle and your transition circuit should be close enough for another test drive. If your A/F reading is close, then swap out your IAB's or raise/lower your primary float to tweak in the A/F number.

Note: If you swap the IFR's, the IAB's, or change the float level, you will need to readjust your metering screws for best vacuum again.


Once you have your under 2500rpm cruise A/F sorted out, then you can work on your steady cruise A/F number above 2500rpm's which should be your main jets. You don't have to cruise at 60, or 70mph to do this. Just drive the car in 2nd and take notes on what your A/F number is at 2500rpms, 3000rpms, 3500rpms, and 4000rpms. Then if your A/F number is off, then make a primary jet swap and then retest again at the same rpms already noted. Then once you have that A/F number and are happy with it, then work on your WOT a/f number.

Have fun!!
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle - 06/12/12 12:52 AM

Ok,I put .015 wires in all 4 IFR`s{.040-dia.} and went back to stock-{78`s}-jetting.
Idle mixture screws are out 1-1/2 turns.
Can`t drive it cause its raining,however :
idle is very good quality at 13.5 AFR
slowly increasing throttle against the converter in 3rd yeilds an AFR of 12.5 up 13.5 at 2,000.
Driving will show what its gonna do but I was seeing 10.9/11.5 doing the same tests stationary before. Soooooo hopefully I`m closer.

Obviously I was making WAY too course of adjustments before. I underestimated how sensitive and small a range a "good" fuel curve is.
I usually only messed with idle and wide-open throttle before the wide-band 02.

Thanks for all the good advise

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Posted By: YO7_A66

Re: Holley Rich at Light Throttle - 06/12/12 01:19 AM

It might take a few tries to get the A/F where you want it but it looks like you might be going in the right direction.
Keep us posted and send some of that rain west to Indiana.

Note: You are going from a LARGE .040" IFR down to a SMALL .025 size. Just a friendly note to be gentle on the accel pedal until you get a chance to watch the A/F meter. That is a BIG jump so you might have to correct it by going smaller on your IAB's.
If this test gets you closer to the A/F that you want but you need to buy IFR's, the .031's, .033's, and the .035's are fairly common sizes sold online. But keep testing with the wire until you know exactly what you need.

Be carefull and let us know what you find.
Posted By: RobX4406

Re: Holley Rich at Light Throttle - 06/12/12 02:25 AM

Quote:

Note: You are going from a LARGE .040" IFR down to a SMALL .025 size.



Putting a .015 wire in a .040 orfice is MUCH bigger than a .025 orfice. You can almost stick 3, .015 wires across the diameter of that hole.

Think surface area. That situation with .015 wire makes the .040 hole about a .037 orfice.
Posted By: joedust451

Re: Holley Rich at Light Throttle - 06/12/12 03:03 AM

Quote:

What worked for me is lean out (restrict) the IFRs until the idle corner screws are around 1.5 turns out. My 750dp jetted properly for wot only had the screws 3/4 turn out and was pig rich on the transfer slot. I don't have jettable ifrs so I have to use wire.



I have found the 750dp to be pig rich in the idle curcuit "stock", I left my IFRs alone & just increase the IABs about .006" front & .003" rear, this is on a 4 corner idle carb, now the front idle screws are 1.1/2 out & has a very clean idle.

My newer 650dp (2 corner idle) had .086" IABs (front) & .055" rear with .035" IFRs, they have really cleaned up the idle on these newer DPs, i had the idle screws out 3 turns & it was really nice, anytime the idle mix screws are 1 turn or less out on any of my holleys & start giving it more air to bring them out, of coarse you can also de-crease the IFRs also.

As for the part throttle AFR adjustment, playing with the PVCRs will help this area.
Posted By: YO7_A66

Re: Holley Rich at Light Throttle - 06/12/12 11:28 AM

""Putting a .015 wire in a .040 orfice is MUCH bigger than a .025 orfice. You can almost stick 3, .015 wires across the diameter of that hole.

Think surface area. That situation with .015 wire makes the .040 hole about a .037 orfice.""

Got it. Thanks for clarifying.
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle - 06/12/12 11:51 AM

Yes ,I`m aware that .040 minus .015 does`nt equal .025 when dealing with area.
That being said I also have no clue what the formula is either

I`ll leave that to my engineer brother

I just know now its smaller
Posted By: JimG

Re: Holley Rich at Light Throttle - 06/12/12 01:29 PM

Based on your info, I'm going to take a guess that during the pig rich light cruise, the throttle is barely cracked open; maybe 1 - 2%?

If not, stop reading now.

If so, you're cruising on the transfer slots, and most likely the main circuit hasn't started working yet; certainly not enough to do much good. As others have said, you can pinch down the transition circuit with t-slot restrictors and such, but before the problem is fixed, you'll create an off-idle lean spot. As others have said, you can help somewhat by reducing the size of the IFR, but again you'll probably lean out the idle circuit too much before the rich cruise is fixed.

Think about the 1-2% throttle position opening, and how that relates to the t-slots. At cruise (the rich spot) you have 12 - 14" hg sucking fuel through the slots, via the IFR. But when pulling away from a stop at the same 1 - 2% throttle opening, you probably have the equivalent of idle vacuum (7 - 8" hg) or less. Orfices that are sized properly for 7 - 8" hg are too big at 12 - 14" hg. So, when you pinch it down so it's "right" at cruise, it'll be too lean off idle at low vacuum.

The idle circuit (including the t-slots) works on manifold vacuum, not venturi airflow. Driving on the t-slots will always be a compromise bacause of this.

This is a very common problem with big Holleys and Holley clones on crisp-running engines that require tiny throttle openings to move them down the road.

Sometimes, ignorance (not having an O2 meter) is bliss, huh?

J
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle - 06/12/12 01:52 PM

Quote:

Based on your info, I'm going to take a guess that during the pig rich light cruise, the throttle is barely cracked open; maybe 1 - 2%?

If not, stop reading now.

If so, you're cruising on the transfer slots, and most likely the main circuit hasn't started working yet; certainly not enough to do much good. As others have said, you can pinch down the transition circuit with t-slot restrictors and such, but before the problem is fixed, you'll create an off-idle lean spot. As others have said, you can help somewhat by reducing the size of the IFR, but again you'll probably lean out the idle circuit too much before the rich cruise is fixed.

Think about the 1-2% throttle position opening, and how that relates to the t-slots. At cruise (the rich spot) you have 12 - 14" hg sucking fuel through the slots, via the IFR. But when pulling away from a stop at the same 1 - 2% throttle opening, you probably have the equivalent of idle vacuum (7 - 8" hg) or less. Orfices that are sized properly for 7 - 8" hg are too big at 12 - 14" hg. So, when you pinch it down so it's "right" at cruise, it'll be too lean off idle at low vacuum.

The idle circuit (including the t-slots) works on manifold vacuum, not venturi airflow. Driving on the t-slots will always be a compromise bacause of this.

This is a very common problem with big Holleys and Holley clones on crisp-running engines that require tiny throttle openings to move them down the road.

Sometimes, ignorance (not having an O2 meter) is bliss, huh?

J



Exactly
I understand "why" its rich. This is where a carb. with metering rods wins! More gear and or a looser converter would let me drive past the trouble spot. I`ll get as close as I can then move on.

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Posted By: JimG

Re: Holley Rich at Light Throttle - 06/12/12 02:21 PM

Quote:

Exactly
I understand "why" its rich. This is where a carb. with metering rods wins! More gear and or a looser converter would let me drive past the trouble spot. I`ll get as claose as I can then move on.



Good deal!

I'm fighting the same problem as you are... or I was fighting before I (in your words) got as close as I could and moved on.

In my case, I'm definitely cruising on the t-slots, and this is a bad deal... impossible to tune. I also have a wider vacuum difference between idle and cruise than you do, making my situation worse than yours.

So, at the risk of telling you what you already know:


"Close" for me was the following: large PMABs, as-small-as-possible IFRs, and I'm using t-slot restrictors, but IIRC they're fairly large (not much restriction).

I have a stock primary metering block with 2 emulsion bleeds in the "classic Holley" location... I have the primary float level set below the level of the top e-bleed. A better fix would be to buy one of those pretty billet metering blocks and move the top e-bleed above the "normal" float level position. This is an attempt to get the main circuit working at lower venturi airflow, and it works, just not well enough.

I have another baseplate with shorter t-slots, same width as stock... some circle track piece I snagged from eBay. I briefly tried that, and it helped the rich cruise situation, but unrelated problems made me switch it back to the stock one, but there is definitely some potential for improvement there if you can find a similar baseplate with shorter t-slots.

Do everything within your power to increase idle vacuum. One of the easiest ways to get a carb tuned better is to minimize the difference between idle vacuum and cruise vacuum. If the idle vacuum is higher, you can further reduce the IFR size and maybe use smaller TSRs before the dreaded off-idle lean spot occurs.

I have all my specs and measurements on an Excel spreadsheet that I can share with you if you're interested.

Good luck with it.

Jim
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle - 06/12/12 02:34 PM

Cool , Thanks!!!! Yes I would be interested in seeing what you have
Posted By: Cab_Burge

Re: Holley Rich at Light Throttle - 06/12/12 06:39 PM

I'm working on a older #9375 non HP 1050 Dominator, I ended up drillinga and tapping the main body to restrict the idle and transfer fuel feeds, I got it to lean to start with Can you say 16.1 and up on idle and light throttle crusie, major bog off idle I do have the idle down to 14.8 to 16.1 now after warming up,part throttle is 14.6 to 15.5 AFR still. I may richen it up a tiny bit more, I'm at 3500 Ft above sea level using Oregon non ethanol pump swill, no noticable pinging or detonation yet, 10.78 to 1 comp. ratio with aluminum heads
Posted By: 6bblFLASH

Re: Holley Rich at Light Throttle ** UPDATE** - 06/18/12 10:11 PM

Made some progress on my rich cruise condition.
Had .040 IFR
.070 AFR
82/96 jets = 11.3-5 cruise AFR

Same as above plus .015 wire in all 4 IFR`s got me a 12.2-5 AFR at cruise.
I can live with that. Will try to go even further later,but runs/idles/ drives and flies really nice!!
Ran a new best of 12.03 @ 111.44 mph. Friday night taking it easy off the line{already broke one driveshaft }.
It will run 11`s at other tracks easily. Quaker is SLOW/uphill.
Columbus is usully worth a 10th or 2.
Anyway,
THANKS for all the help

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Posted By: radar

Re: Holley Rich at Light Throttle ** UPDATE** - 06/19/12 01:56 AM

Electric guitar 'B' string. They sell all different gauges I am currently using .017
Posted By: YO7_A66

Re: Holley Rich at Light Throttle ** UPDATE** - 06/19/12 11:33 AM

""Same as above plus .015 wire in all 4 IFR`s got me a 12.2-5 AFR at cruise.
I can live with that. Will try to go even further later,but runs/idles/ drives and flies really nice!!""

You leaned it out 1 full point at cruise, nice!! When you get some time, you might want to try and get into the mid-high 13's at cruise and see how it reacts, then reset your WOT A/F.
Congrats!!
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