Moparts
Help with A/F Ratio Numbers
Posted By: charger_dart
Help with A/F Ratio Numbers - 08/25/11 03:05 PM
I hooked up a NGK Air Fuel ratio guage to my 500 wedge motor with a Holley 80531 850 carb (vacuum secondary) The numbers I got were:
Idle - 13.5
Cruise - 12.5
Light throttle - 13.5
Decelerate - 11.5
WOT - 13.5 dropping to 12.5 as the secondaries open
Do these look like good numbers? This carb replaced an Eddy 800 and seems to run pretty good right out of the box.
Thanks for all comments
Posted By: Mopar_Rich
Re: Help with A/F Ratio Numbers - 08/25/11 04:01 PM
Quote:
Idle - 13.5
Cruise - 12.5
Light throttle - 13.5
Decelerate - 11.5
WOT - 13.5 dropping to 12.5 as the secondaries open
The cruise is too rich. That will hurt mileage. Idle should be about 14 to 14.5 (depends on what the motor wants) and your cruise should be about the same as idle, maybe a tad richer.
The WOT is fine.
The decel is showing rich only because there's excess fuel being burned off. On a long decel, given time to burn off the fuel, the AF ratio should go as lean as idle.
Posted By: YO7_A66
Re: Help with A/F Ratio Numbers - 08/25/11 04:27 PM
I started out with my in D idle around 14.2-14.4 but my rpms would jump around too much so now I keep it around the 13.6-13.8 range. My N idle is usually a tad leaner 13.8-14.0 or so.
My cruising range is 14.2 to 15.5. Anything close to 16 and I get worried and retune.
My light throttle feels more responsive in the 13.6-13.8 range. I have tried as lean as 14.4 but it just felt a little soft.
My decel gets down to 13.5 or so.
Once you lean out your cruise then the decel should lean out too.
Posted By: charger_dart
Re: Help with A/F Ratio Numbers - 08/25/11 05:05 PM
Thanks for the comments. That's kind of what I thought - So maybe a jet change on the primary side will get me into a better condition?
Currently I have 78's on the primary side and 82's on the secondary side. What jet size should i try to go to?
Posted By: YO7_A66
Re: Help with A/F Ratio Numbers - 08/25/11 05:17 PM
You should see an immediate change on the A/F meter if you go at least 2 jet sizes and if you test with the same outside temps. But if the meter stays with the same reading, then the transition circuit would need to be tuned instead of the primary jetting.
Posted By: charger_dart
Re: Help with A/F Ratio Numbers - 08/25/11 08:12 PM
Quote:
You should see an immediate change on the A/F meter if you go at least 2 jet sizes and if you test with the same outside temps. But if the meter stays with the same reading, then the transition circuit would need to be tuned instead of the primary jetting.
Ok, I will put 76's on the primary side and see what readings I get. Thanks!!
Posted By: YO7_A66
Re: Help with A/F Ratio Numbers - 08/25/11 08:38 PM
Keep lowering your primary jetting until you get the cruising A/F that you want. Then you will have to go back and recheck your secondary jetting for your WOT A/F since you are removing jet out of the primary side of the carb.
Posted By: charger_dart
Re: Help with A/F Ratio Numbers - 08/26/11 12:18 PM
I don't believe this! I pulled my NEW carb apart for the first time to change the jets and found the primary float has been crushed. It had barely 1/8" of movement!!
Where is the quality control at Holley???
Posted By: Cab_Burge
Re: Help with A/F Ratio Numbers - 08/26/11 05:25 PM
I have a Innovate dual wide ban on my car, I like to see 14.5 or leaner at idle and close to that at part throttle, 12.8 to 13.3 at WOT makes my car run the fastest at the track
It is a pump gas car that runs in the low tens at 133. MPH so far
As far as the float have you had the car real hot since putting that carb. on
also did you buy it(the carb.) new? I have seen several floats ike that in used carbs.
I don't think Holley has used brass floats in there new carbs. in a lot of years due to the fuel mixes that are used today, IE alholol
Posted By: charger_dart
Re: Help with A/F Ratio Numbers - 08/29/11 08:26 PM
Quote:
I have a Innovate dual wide ban on my car, I like to see 14.5 or leaner at idle and close to that at part throttle, 12.8 to 13.3 at WOT makes my car run the fastest at the track It is a pump gas car that runs in the low tens at 133. MPH so far As far as the float have you had the car real hot since putting that carb. on also did you buy it(the carb.) new? I have seen several floats ike that in used carbs. I don't think Holley has used brass floats in there new carbs. in a lot of years due to the fuel mixes that are used today, IE alholol
Thanks for posting what numbers work well for you. I also run pump gas in my car.
The carb was purchased new from amazon.com and I can't think of what would of caused it to crush like that. Its as if it was sent to the bottom of the ocean or something. The replacement float came air freight and was brass also - in perfect condition!
Now I just have to see what effect the jet change and float fix has had. Will post pack later.
Posted By: FK5
Re: Help with A/F Ratio Numbers - 08/30/11 12:04 AM
Sorry if this is a bit of a hijack, but I'm interested in messing around with a wideband. I would hope to be taking it car to car, but cars I want to start out with already have narrow band sensors. Will I still be able to get a usable signal to computer? How's it work?
Posted By: dogdays
Re: Help with A/F Ratio Numbers - 08/30/11 12:19 AM
You're at close to sea level. I bet you don't need to change jets at all. Just change the float and go for a drive. Those new Holleys are pretty close out of the box.
My Holley was running way rich. I found the secondary float stuck open, I was getting fuel injection (well, kind of) out of the secondary side. I cleaned the needle and seat, reset the float and the condition went away.
R.
Posted By: 451Mopar
Re: Help with A/F Ratio Numbers - 08/31/11 08:13 AM
Does holley have a quality control department?
My Truck Avenger did not run right either.
When I pulled it apart there were two brass slugs in the jet wells behind the jets
Posted By: AndyF
Re: Help with A/F Ratio Numbers - 09/01/11 12:28 AM
The problem you'll have is doing anything about those numbers. To lean out the cruise you'll most likely need to reduce main jets by a size or two, but when you do that the WOT will be too lean. To fix the WOT you'll need to open up the PVCR restriction. On the Ultra carbs you can change jets in the metering block but I don't think a 80531 will have jets in the PVCR. You'll probably have to do a little drill work to get that carb dialed in just right.
Of course, you might get lucky. Start by leaning out the idle and see if that fixes the cruise also. If it does then you might be fine at WOT.
Posted By: RobX4406
Re: Help with A/F Ratio Numbers - 09/01/11 12:52 AM
You likely won't get it refined by changing main jets, especially if your cruise rpm is in the 2500 or less range.
A side note: The HP series holleys are horribly rich pigs on cruise and main jet change don't clean them up.
Posted By: YO7_A66
Re: Help with A/F Ratio Numbers - 09/01/11 02:30 AM
If leaning out the main jets does not lean the A/F number, then the IFR's need to be smaller. The IFR's control the transition circuit which is activated after the idle circuit and before the main circuit.
Posted By: AndyF
Re: Help with A/F Ratio Numbers - 09/01/11 02:41 AM
It is quite possible that the main jets aren't doing much at 2500 rpm. Every combo is different but even a 500 inch motor might not be pulling much fuel thru the mains at cruise. If that is the case then the idle circuit is the one to pay attention to.
Once again, those cast metering blocks are going to be a hurdle. The Ultra Holley carbs have idle jets in the metering blocks which can be quickly changed. The other Holley carbs have pressed in restrictors which are not that easy to modify.
Posted By: RobX4406
Re: Help with A/F Ratio Numbers - 09/01/11 03:09 AM
Quote:
If leaning out the main jets does not lean the A/F number, then the IFR's need to be smaller. The IFR's control the transition circuit which is activated after the idle circuit and before the main circuit.
Yep, and the blocks aren't that tough to alter to make them adjustable. Need the tools and brass and you're off and running.
Posted By: dodgeboy11
Re: Help with A/F Ratio Numbers - 09/01/11 03:06 PM
For WOT tuning I like to have a dyno. The A/F ratio numbers are nice to have, but the dyno tells the story. Tuning for max power may want more fuel or it may want less. But I like to tune for it and that way I know which way I can safely go (richer or leaner) to tune for fuel economy and not hurt the motor when I do have my foot in it. It's often a compromise with a carb.
Posted By: 74_360_Cuda
Re: Help with A/F Ratio Numbers - 09/01/11 10:26 PM
Guys, I have been playing for years with my QF-750 and my LM2 and was wondering how can I make the part throtle richer while making the idle leaner?
I Have changed my IFR down to 31's, my idle screws are still only about 3/4 of a turn to have 14 at idle but my part throtle is too lean...
Also, my primary accelerator pump does not perform as well as the seconday... If I tap on the plunger with my finger I have an immediate spray on the secondary pump but not on the primary. I have changed all the parts for new parts with no improvement (diaphragm, valve, needle valve etc...) and there is no gap between the plunger and the arm...
Posted By: 74_360_Cuda
Re: Help with A/F Ratio Numbers - 09/01/11 10:32 PM
Quote:
The problem you'll have is doing anything about those numbers. To lean out the cruise you'll most likely need to reduce main jets by a size or two, but when you do that the WOT will be too lean. To fix the WOT you'll need to open up the PVCR restriction. On the Ultra carbs you can change jets in the metering block but I don't think a 80531 will have jets in the PVCR. You'll probably have to do a little drill work to get that carb dialed in just right.
I did that on mine with great results, I had to increase the holes a lot to have same A/F ratio as the secondaries at WOT but now I can cruze at 14.5... You will have to try differant PV setting to see what your engine prefer... right now I have 6.5 but I would like it to open sooner so I will try 8.5
Posted By: charger_dart
Re: Help with A/F Ratio Numbers - 09/07/11 02:08 PM
Well, sorry for the delay, had to wait for Holley to send me a replacement float. I checked the float on the secondary side and it was fine.
I did change the primary jets from a 78 to a 76 and leaned the idle a little then retested.
The numbers did improve some, but my cruise is still rich and did not change. I have a 4 speed automatic with an overdrive so my cruise is around 1800 at 50 mph so maybe the primary jets are not having an effect?
I have never attempted drilling the plate and not real sure I want to do that without knowing what to do.... Suggestions??
Posted By: YO7_A66
Re: Help with A/F Ratio Numbers - 09/07/11 03:16 PM
""I did change the primary jets from a 78 to a 76 and leaned the idle a little then retested.
The numbers did improve some, but my cruise is still rich and did not change. I have a 4 speed automatic with an overdrive so my cruise is around 1800 at 50 mph so maybe the primary jets are not having an effect?""
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At 1800rpms, you may not be on the main circuit, especially if your cruise A/F did not get any better. Do you have replaceable IFR's in your Holley 80531 850 carb? If not, then you might want to investigate how to modify your metering blocks or invest in a set of metering blocks that gives you more tunability.
You are getting to the point that you have the tool to tell you where your carb needs tuned but you don't have the ability to make use of the information unless you invest in some parts for your carb.
Before you do so, you might want to make a chart and do some testing to make sure that you are not on the main circuit. If you were to go test drive your car with the jets that you have in it now, then at a steady cruise, or with your over-drive, at a steady RPM, take an A/F reading at say, 1500, 1800, 2000, 2500, 3000, 3500rpms. Then swap out your jets to larger or smaller and then take the A/F readings again at the same rpms. Once you make the second test, you should be able to see a change in A/F numbers on your chart. When you see the A/F numbers change, then that is when your main jets are activating. If this rpm is above your current 1800rpms, then you know that your mains are coming in higher in the rpm range and you need to decide how you can change the A/F range below the 1800rpms. This would need to be done with the IFR changes.
Posted By: greg_moreira
Re: Help with A/F Ratio Numbers - 09/07/11 03:29 PM
Your main jets arent doing much of anything at that cruise rpm. Your still on the idle/transfer circuit with that little throttle opening/cruise rpm.
The idle mixture screws themselves will have influence on both cruise and idle, as will the idle feed restrictor(IFR as previously mentioned in this thread).
Try this trick.... go to your local music store and buy some individual guitar strings.
Buy and .008, a .009, and a .010. Cut out some one inch sections or so in the wires. Start with the .008. Slip the wires into the idle feed restrictors in the primary metering block, bend it over(so it lays against the block) and sandwich it in place with the gasket and put the carb back together. By having reduced the IFR's by .008 you will definitely begin to see a change in the idle and light cruise numbers.
It may act too lean at this point, and you can actually fatten up the idle mix screws to whatever the motor likes. This is a test. Slip them wires in to get a good idea of what the motor wants....and then you can permanently modify the size of the IFR(drill and tap for jets).
Posted By: AndyF
Re: Help with A/F Ratio Numbers - 09/07/11 03:33 PM
If you buy a set of modern metering blocks then you can quickly adjust the jets in all of the circuits. Idle, intermediate, PVCR, etc.
Posted By: mrob
Re: Help with A/F Ratio Numbers - 09/07/11 03:45 PM
To add onto what greg said: after you have an idea how big the IFRs need to be, you can remove the pressed-in IFRs and make your own removable IFRs by drilling orfices into 8-32 brass set screws and installing them. A good source for the set screws is McMaster Carr.
Posted By: RobX4406
Re: Help with A/F Ratio Numbers - 09/07/11 05:37 PM
Quote:
To add onto what greg said: after you have an idea how big the IFRs need to be, you can remove the pressed-in IFRs and make your own removable IFRs by drilling orfices into 8-32 brass set screws and installing them. A good source for the set screws is McMaster Carr.
I prefer 6-32 for the IFR, especially if they are the diagonals in the upper part of the metering block. Leaves a bit more material around the hole. You can get as big as .040-.045 orfice in the 6-32 set screws, IIRC.
If you do the 8-32 IFR's it comes in handy for Power Valve Channel Restrictors as well.
Here's something to ponder. If you have a .041 hole and stick a .025 wire in it, what's the relative diameter of the new orfice?
If you guessed it's .016, try again. Get used to the area of a circle formula.
It's interesting chasing this stuff with carbs. Make an adjustment in one system and it changes other areas of the curve.
Those LM's are a great tool and can become a curse when you really try to refine it. OCD people should stay away from them. LOL
Posted By: AndyF
Re: Help with A/F Ratio Numbers - 09/07/11 06:14 PM
No need to drill set screws, just buy them from BLP.
BLP has 6-32 and 8-32 brass set screws already drilled. They stock a large selection of both sizes as well as a ton of other types of jets.
If you're into carbs, the BLP website should be bookmarked. It is a wealth of information. They have so many parts available for Holley type carbs that I'm not sure how they even keep track of them all.
Posted By: RobX4406
Re: Help with A/F Ratio Numbers - 09/07/11 11:15 PM
BLP is a great source for parts.
I do the Mc-Master Carr thing because it's much less money than buying these things for $1-2 each at a time.