Air/ fuel tuning

[ap6street]

hey everyone does anyone have any experience tuning with a air/fuel gauge in car?
have mine hooked up
innovate lc-2 wideband.
idles good about 14:1
cruise is 13 - 13.5
and wot is around 12.8

as for driving around the street the gauge jumps a lot and at very light throttle and off idle , gauge reads 10.5 and 11 s quite a bit.

seems to drive fine, plugs seem ok.
probably not to worry , but any suggestions ?

idle mixtures are 1 turn out
5.5PV
78/86jets
idles 1400neutral 1000drive
28locked timing



410sbm
266/272 630/630 110
indy heads
950 custom carb
13/4headers
12:1comp

 

[TrailBeast]

What carb?
It looks like you could go one size smaller on the jets to get it into the high 14's-low 15's at light cruise.
Everywhere else looks pretty good, and that off idle 10.5-11 is probably your accelerator pump shot richening it up.

You are generally pretty close, so don't get to anal about the numbers or it'll drive you to drink.
It'll NEVER always be right where you want it.

 

[72bluNblu]

What carb?
It looks like you could go one size smaller on the jets to get it into the high 14's-low 15's at light cruise.
Everywhere else looks pretty good, and that off idle 10.5-11 is probably your accelerator pump shot richening it up.

You are generally pretty close, so don't get to anal about the numbers or it'll drive you to drink.
It'll NEVER always be right where you want it.

Exactly!

I’ve got an innovate LC2 in my Duster. You can absolutely drive yourself nuts. The Holley 750 DP I run is pretty temperature sensitive, I go up and down on the primaries for summer and winter. And in the spring and fall I usually leave the winter setting in place so it starts better cold.

That said, I agree with trailbeast. You’re pretty close already, you can probably drop a size on the primaries to get better mileage at cruise. Your accelerator pump may be too big or too sensitive, the carb type will change how you deal with that. On a Holley I’d look at the pump cam and nozzle. A pump cam with a slower ramp may help, or just a downsize on the nozzle.

 

[TrailBeast]

Exactly!

I’ve got an innovate LC2 in my Duster. You can absolutely drive yourself nuts. The Holley 750 DP I run is pretty temperature sensitive, I go up and down on the primaries for summer and winter. And in the spring and fall I usually leave the winter setting in place so it starts better cold.

That said, I agree with trailbeast. You’re pretty close already, you can probably drop a size on the primaries to get better mileage at cruise. Your accelerator pump may be too big or too sensitive, the carb type will change how you deal with that. On a Holley I’d look at the pump cam and nozzle. A pump cam with a slower ramp may help, or just a downsize on the nozzle. But that’s for a Holley.

And the Edelbrock Performers would take one size larger needle, or one jet size smaller.

 

[72bluNblu]

And the Edelbrock Performers would take one size larger needle, or one jet size smaller.

Yeah he mentioned he’s got a power valve though, so it’s probably some kind of Holley based carb. 950 custom? But we still don’t know if it’s mechanical or vacuum secondaries, size (or number) of the accelerator pump nozzles, pump cam etc...

 

[TrailBeast]

Yeah he mentioned he’s got a power valve though, so it’s probably some kind of Holley based carb. 950 custom? But we still don’t know if it’s mechanical or vacuum secondaries, size (or number) of the accelerator pump nozzles, pump cam etc...

Yep, duh.

 

[72bluNblu]

Yep, duh.

I missed it the first time through too.

Some of it depends on your engine too, I mean, I don't run mine as lean as I can because I'm closer to detonation than I wanted to be. It also depends on the carb. I spent months (on and off) trying to deal with an off-idle spot with my 340. It was either too rich or too lean, never could get it right. I tried both a 670 street avenger and a 770 street avenger. With both I had no issues tuning idle, cruise and WOT, but off idle I was sunk, same with transitioning from cruise to WOT. Then I found some other folks with low(ish) idle vacuum engines and 4 speeds that had issues with tuning vacuum secondary carbs. I went to a mechanical secondary 750 DP and had it well sorted in a couple days.

 

[crackedback]

28* locked out? That will make it run rich if it needs more timing to be efficient.

The carb may need a LOT of adjusting to the air bleeds, idle feed restrictors and main well/emultion bleeds.

 

[ap6street]

holley 950 main body
mech secondaries
high speed bleed 33
idle air bleed 68
idle feed restriction 36
acc pump 30/50
pump cam 330/660
squirter size 32/35

yeah i dont recall anything that low when i was cruising in the cooler days.

dropped 2 jet sizes since then already to get it to where it is now from winter.

 

[ap6street]

yeah 28 locked timing.
was most hp on engine dyno.

whats the best way to know if it wants more

 

[TrailBeast]

I missed it the first time through too.

Some of it depends on your engine too, I mean, I don't run mine as lean as I can because I'm closer to detonation than I wanted to be. It also depends on the carb. I spent months (on and off) trying to deal with an off-idle spot with my 340. It was either too rich or too lean, never could get it right. I tried both a 670 street avenger and a 770 street avenger. With both I had no issues tuning idle, cruise and WOT, but off idle I was sunk, same with transitioning from cruise to WOT. Then I found some other folks with low(ish) idle vacuum engines and 4 speeds that had issues with tuning vacuum secondary carbs. I went to a mechanical secondary 750 DP and had it well sorted in a couple days.

Funny, almost exactly the same here with the timing and running just on the rich side
for detonation reasons and temperature reasons.
I drop 2k feet when I go to Phoenix and don't want to have to change timing or fuel grade when I go down there.
Man I'll tell ya, 2k feet lower elevation changes the engine personality.

I run in the average hi 15's at cruise down there, but the hi 14's where I live at 5,500.

 

[crackedback]

I'd go to a .032-.033 IFR and see what it does.

Make sure the A/F meter has a clean power and ground run. They can be very finicky if the power is varied when in operation.

 

[ap6street]

firstly where can i buy the idle feed restrictors , mine has allen key head ones.
its a kb carburetors carb? any opinions?
so the carb was built to suit and then dynoed so i dont want to get too over my head.

was cruising on the freeway today, and at 60mph about 3100rpm, cruise was always min 12s maybe even low 12s so after about 100kms , i decided to try a smaller jet .
put in a 76/86 combo now.
cruise changed to 13:1
but for WOT
cruising at 3100rpm , then full throttle
i get 14.5 approx , but after 2 seconds of WOT it drops to a safer 12.5.

should i just put the 78's back and leave it or ???

vaccum is around 10.5at idle

 

[ap6street]

i will also mention engine was dynoed, but that was with ngk 8s and straight out the headers.

i now run a 6heat range and a full length 2.5" twin exhaust system

 

[yellow rose]

firstly where can i buy the idle feed restrictors , mine has allen key head ones.
its a kb carburetors carb? any opinions?
so the carb was built to suit and then dynoed so i dont want to get too over my head.

was cruising on the freeway today, and at 60mph about 3100rpm, cruise was always min 12s maybe even low 12s so after about 100kms , i decided to try a smaller jet .
put in a 76/86 combo now.
cruise changed to 13:1
but for WOT
cruising at 3100rpm , then full throttle
i get 14.5 approx , but after 2 seconds of WOT it drops to a safer 12.5.

should i just put the 78's back and leave it or ???

vaccum is around 10.5at idle

Just buy some 6/32 X .187 brass set screws and the appropriate sized drills and make your own IFR's. If you have the same style in the emulsion you can make those as well. If you have flanged air bleeds you can order blanks and make those yourself as well.

 

[MOPAROFFICIAL]

i will also mention engine was dynoed, but that was with ngk 8s and straight out the headers.

i now run a 6heat range and a full length 2.5" twin exhaust system

The exhaust is choking it. Run 3 inch pipes.
The rich transitional blips of 10-11afr is the pump shot. The timing is ttpical for a closed chamber quench setup, it's burning faster. You could get it a hair better idle afr, but from the combo...you are good.

 

[ap6street]

What about the 14.5 spike when hitting the throttle wot.??
Will this cause some damage ?

 

[mullinax95]

What about the 14.5 spike when hitting the throttle wot.??
Will this cause some damage ?

I can't answer your question but have just installed a wideband on my 03 Dodge Ram with 5.9L and I see all kinds of readings. Most part stays right at 14.7 because of the ECM doing it's thing but I never knew air/fuel ratios swung so much.
I find this thread interesting because I have another wideband ready to be installed on my cuda. I think as long as you don't stay in the 15 or 16s at WOT for a long period of time you're OK. I believe I would try to have the spike richer than what you have at WOT but I'm not a guru when it comes to this topic.

 

[crackedback]

From a dead stop?

Is the spike rolling into WOT or matting while from a cruise?

Dead stop, acc pump, squirters and cams.

From a roll, try a higher number power valve in it.

 

[Mattax]

I'd go to a .032-.033 IFR and see what it does.

at gentle off-idle and steady crusing under 40 mph.

However I'm also seeing a lot more (as is Crackedback). It all depends on what you're after and what you're into. If you enjoy tuning that's different than if you just want it to run in a way that you like driving it.

So, after looking at your engine specs, here's how I look at what you've reported:

28 locked timing
idles good about 14:1
idles 1400neutral 1000drive
vaccum is around 10.5 at idle
as for driving around the street the gauge jumps a lot and at very light throttle and off idle , gauge reads 10.5 and 11 s quite a bit.
​

The idle AFR is really 10.5 to 11 that you saw in off-idle while driving. Opening the IABs a hair may lean that out a bit. Idle should be rich, especially with that cam. Whether its 11 something or 12 something or 13 - that you have to experiment with as your engine is different than the next guys. If its too lean, it will hesitate or miss when gently coming off idle.

cruise is 13 - 13.5
was cruising on the freeway today, and at 60mph about 3100rpm, cruise was always min 12s maybe even low 12s so after about 100kms , i decided to try a smaller jet .
put in a 76/86 combo now. cruise changed to 13:1​

At least you know the main circuit is taking over from the idle circuit when cruising at 60 mph. If you want to work on this, keep taking them leaner until the engine tells you its too lean by surging. Do this some place you can slow down and even pull over. You'll have to change the jets or drive back at a slower speed. Do NOT test WOT.

If you find the jetting for high speed cruising is different than best power (on the dyno), then change the power valve restrictions. If the best power was with 78 and your most efficient cruising is 75, then the PVCRs get enlarged.

and wot is around 12.8
​

If that's where it did best on the dyno, then that's a good baseline when you go to the strip. Tune to the best mph, not the AFR.

then full throttle
i get 14.5 approx , but after 2 seconds of WOT it drops to a safer 12.5.​

Same question as crackedback asked But also, how did it feel? Several posibilities here. Also depends how you pedelled it open. While driving, the deeper the part throttle, the more it goes lean until its getting close to fully open, then the power valve opens so its richer by full throttle. That's the way it should be.

idle mixtures are 1 turn out​

As long as the screws are responsive, I don't get too hung up on this. Just keep track of the changes.

firstly where can i buy the idle feed restrictors , mine has allen key head ones.
its a kb carburetors carb? any opinions?
so the carb was built to suit and then dynoed so i dont want to get too over my head.

Sounds like buy and drill type.
The dyno, unless your dealing with someone very skilled and it has a load cell, isn't all that helpful for the part throttle and low speed stuff. If the carb was built to suit and then dynoed as you write, then it sounds like no tuning was done on the dyno other than jetting. Get a hold of the dyno logs if you can. If its a Dynojet brand, get the files so you can examine at your leasure on your computer. The others I don't know but they may also have programs to let you read the files.

Make one change at a time. Keep written notes as you already are doing, and you'll be fine. Worst case you return it to your baseline. Testing often includes a few dead ends.
Lets say you start with the slightly smaller IFRs, then make no other changes except tweaking the idle mix screws if needed. Go do your low speed tests, and then if driveable, see how it cruises at higher speeds.
If you're doing the main jets, don't change the IFRs. If you change the IFRs, don't change the main jets. Only exception would be if you wanted to put the jets back to the baseline.
Idle Air Bleeds are a finer adjustment than the Idle Restrictions. Even though they work hand in hand, just change one or the other.

Fuel Air Ratio to Load graph
How to download Dynojet Reader

Thinking about the .036 IFRs, something to consider
Relocating the Holley Idle Jet - racingfuelsystems.myfunforum.org

 

[MOPAROFFICIAL]

Another novelist.
That could have been a lot shorter and with alot less cornhole smooching.
You have one foot in and one foot out
Those things you echoed aren't being recycled here because he has an afr gauge, he doesn't need to lean the jetting till surge and back up 2 because the gauge will tell him how which way to go and how far.

The pump cams could be a hair off from ideal when it comes to the pump shot curve, even near 40 mph as could be the power valve rates too low and is late on enrichment.

Does it lean blip stomping on it at 70mph?

 

[ap6street]

thanks for all the replys.
probably wont have the car back out for a few days.
ive chaned the powervalve to a 6.5 as that sounded like the easiest thing to try first.

im assuming here because the lean spike is from a high speed cruise , you dont get a full pump shot and therefore more relying on the powervalve to enrich the quick change ???

also you said the powervalve restrictions? is this related to the amount of extra fuel the powervalve allows through?


if after the initial spike drops down the air/fuel drops to the 12.5 , possibly was even 12.2
ill have to bring some paper or a cam to get these records as i go.
would a drop in the secondaries be a good idea?

its just that would bring it from
dyno: 82/86
to 76/84
is that way too much , dont want any lean issues.

and yes i do enjoy trialling things back and forth especially if i got a bit of an idea of whats going on , but just want to know the limits of lean mixture before i do damage

 

[Mattax]

im assuming here because the lean spike is from a high speed cruise , you dont get a full pump shot and therefore more relying on the powervalve to enrich the quick change ???

Yes and no. Correct that generally there is less pump shot the more the more the thottles open. How much less depends on the shape of the pump cam. The pump shot is needed to cover the slowness of the idle circuit in responding to changes in throttle. Its not needed so much, or at all, when most of the fuel is coming out of the boosters. (If the main circuits are not responsive enough, the pink cam is one that can be used - but it gives up low opening movement to do so.)
The Power Valve is different. It stays open as long as the manifold vacuum is low. In your case, when the manifold vacuum drops below 6.5"Hg, the valve will open. This allows more fuel into the main circuit.

also you said the powervalve restrictions? is this related to the amount of extra fuel the powervalve allows through?

Exactly. These are like another set of jets in the main circuit. They control the amount of enrichment.

would a drop in the secondaries be a good idea?

I wouldn't touch them until you're done with the primaries.

and yes i do enjoy trialling things back and forth especially if i got a bit of an idea of whats going on , but just want to know the limits of lean mixture before i do damage

At light throttle, the engine will miss or die if its too lean. The danger to the engine is when its at or near full throttle. Don't test the lean limits for that. For full throttle, just make small changes around that 12.8 it ran good at on the dyno. Test at the track to see if richer or leaner it makes faster and test richer first. I'd be cautious if its much leaner than 13.2 at WOT. and of course check the spark plugs for any evidence of problems.

 

[yellow rose]

thanks for all the replys.
probably wont have the car back out for a few days.
ive chaned the powervalve to a 6.5 as that sounded like the easiest thing to try first.

im assuming here because the lean spike is from a high speed cruise , you dont get a full pump shot and therefore more relying on the powervalve to enrich the quick change ???

also you said the powervalve restrictions? is this related to the amount of extra fuel the powervalve allows through?


if after the initial spike drops down the air/fuel drops to the 12.5 , possibly was even 12.2
ill have to bring some paper or a cam to get these records as i go.
would a drop in the secondaries be a good idea?

its just that would bring it from
dyno: 82/86
to 76/84
is that way too much , dont want any lean issues.

and yes i do enjoy trialling things back and forth especially if i got a bit of an idea of whats going on , but just want to know the limits of lean mixture before i do damage

How did you determine you need a 6.5 power valve? I have ~ 10 inches of idle vacuum and I'm using a 10.5 PV and may need to go to a 12.5. Seems to me unless you have very little cruise vacuum you still need an earlier opening PV.

 

[MOPAROFFICIAL]

The pump shot is needed to cover the lag in vacuum signal to the MAIN circuit during moments of low vac/signal from throttle position changes. The power valve is exactly that, under hard ubrupt 'full throttle' load it will supply extra fuel straight from the bowl through the boosters till the mains catch up and signal raises above the PV rating and then closes it.

Fixed.
If you see that rich blip but it only lasts a sec or 2 then gets to 12.5.....leave it unless you can feel it's negative effect.....or go ahead and play with pvr's.
As for the jetting, I run a 750 w/ 75/84 at sea level. Depending on what carb cfm you have...that doesn't seem off.