Lean idle. Rich cruise.

[Newbomb Turk]

Modern gauges should all read the same to within a tolerance that is small. A modern wideband sensor comes paired with a calibration module in the plug connector. they etch off a chunk of some resistor or chip in the plug connection section to get it calibrated
that connector and sensor are now paired for life

usually a warning sticker saying do not disconnect this bit disconnect the wire at the other end of this part with the flip up clip weather proof connector

what happens is someone then takes 1 sensor ignores the warning sticker or it comes off and then swaps the connector bit along with the wire to another sensor and you end up with something that is way way out
i.e you have 3 parts
the wire harness
the plug bit
and the sensor that bolts into your headers

The majority of the plug bit is married to the sensor and is there to provide calibration BUT can be removed if you are persistent enough

most of the screw in wideband sensors will be bosch or similar these days and they do put effort into getting it right. when they make the sensor they don't know if its going into a aftermarket kit or its going into a box of 5000 to be delivered to Peugeot/FIAT for the challenger production line, they all need to be calibrated correctly because the ECU they usually connect to, expects them to be.

AEM and similar all use a chip and LED based gauge, again the tolerance stack up in the circuit will be tiny and inconsequential.

in the past or with unknown history, or cheap knock-off/fake ..... ????

new stuff as in last 10-15 years should be pretty accurate

Dave

Modern doesn’t mean good. Just like anything electronic, it has a wide range of acceptable tolerance.

Tuning to a number, any number is a fools errand

 

[Dave999]

I agree

my use of modern was to cover lambda sensors produced for OEM use by big players in the supply chain

rather than the older narrow and wide band sensor that were produced to work with a very specific ECU or gauge system which were quite rightly bespoke jobs for the application in hand.

since then they have become almost universal fitment and its a damn sight easier to just standardise the sensor than it is to tweak the software on every ECU

its a bit like the original OBD set up with its manufacturer specific plug and codes and the eventual closer standardisation of OBDII

every car has its own unique codes but the majority applicable to all cars in the range or indeed across car companies using an ECU from a supplier common to both will have a reasonable amount of standardisation. you can now buy a code reader that works reasonably effectively across a wide range of manufacturers rather than having to get one for each.

Economics and the need to "Plug n Play" on the production line, drives standardisation

a modern wideband sensor is a 3 or 4 wire unit 1 signal 2 heater and on the 4 wire job the 4th is earth for the signal partner wire

Dave

 

[Mattax]

12.3 cruise and 14.5 idle after opening the idle mixture screw about a 1/4 turn

Idle screws are at 7/8 out now. Turning them out makes cruise richen up.

Changing the idle mix screws changes the cruise AFR means the speed your are calling cruise is still mostly on the 'idle circuit'. It should really be called low speed or low throttle circuit, and in fact that's the term Chrysler often used.

91 pump gas. Pump says contains no ethanol. Thanks

Only reason to avoid the ethanol is if you're not using the car much. Even avoiding the E, using pump fuel you still are dealing with relatively poor lifespan and the seasonal changes. On the other hand, if your car can run WOT in top gear on 91, then that's working out with timing curve on the engine, fine.

There's a sequence to tuning the carb that is useful. It reduces the iterations and dead ends in chasing (changing) because its based on the circuits interact. For example, fuel level effects everything. Next, all fuel exits the bowl through the main jets until enrichment is needed (PV opening). However, the restriction of the main jets is very large (or should be) compared with the idle restriction. So when we work on the idle circuits we can ignore the main jet. Without going further I think you get the idea.

1. Focus on getting the idle to run strong. This is defined as lowest reasonable rpm it will go into gear with the minimal drop in vac and rpm. Easy to test with an automatic transmission. With a manual trans to some degree you'll have to trust the automotive engineers - idle should be relatively rich - especially compared to emmissions era stuff. I wouldn't trust the WBO2 AFR number too much at idle but anything from 12 to 13.5 is at least in the ballpark. As long its not soot up the spark plugs it can even be a little richer if that's what's needed. The reading will change when placed in gear because of the loss of manifold vacuum = less pressure difference on the idle circuit.
1a. I'd work on the primaries as much as possible. The secondary fuel mix is helpful with low manifold vac but don't be afraid to restrict those screws further in that the others, becuase fuel distribution on the idle circuit is more about vacuum than air velocity. On the other hand the primary side is critical in getting the off-idle correct.
1b. Off - idle and idle is going to be controlled by IFR, IAB and the transistion slot exposure. So measure the primary transition slot exposure and make some adjustments with that to see the effect on idle.
2. Check the impact of the idle tuning on off-idle. Should be able to slowly accelerate from closed throttle to 35-45 mpoh without hesitations or sluggishness.
3. Main circuit. Depending on the car and gear ratios, Cruising on the primaries will be interstate speeds. At least 55 mph in my experience, at 60 - 65 mph should be enough load and throttle that most of the fuel is coming through the boosters.
4. Enrichment is full load/max acceleration in at least 2nd gear, preferably 3rd. This is 1/4 mile time (mph) or chassis dyno time.

 

[clementine]

 

[Mattax]

PS. Even when cruising, when there is a slight downhill and we lighten up on the throttle, a high vacuum is created under the mostly closed throttles and guess what happens.



There's less air mass coming through and more vacuum at the idle port and transition slot so the 'idle circuit' starts supplying fuel again.
I've posted some data tables showing that if your interested.

The better we can get the idle circuit to work at idle, the closer we can get the idle vacuum to where the idle system will choke. Choke in this sense is the pressure difference where increasing pressure no longer pushes more fuel through.

 

[aaronk785]

Going to rework my distributor and start over. I rechecked my timing and things aren't right. Think it has a broken spring or something. Very inconsistent. I'll let you kno×what I find.

 

[Ironmike]

I revived this post as I'm having a similar problem. running an XP850 and perfect at idle, perfect at WOT, but pig rich at cruise. Like 11 to 1 ish. Light 4 speed car with 4:30 gears. Timing locked at 33 degrees.

Tried changing air bleeds, P Valves....all for naught. Jetted primary from 84 to 77 and cruise was fine but any "spirited" acceleration on just the primary got dangerously lean.

So carb is now back to box stock config, hoping to fin a fix for my issue. Wondering why the PO blocked the middle emulsion? I'm carb stupid when it involves anything other than a jet change.

 

[Newbomb Turk]

I revived this post as I'm having a similar problem. running an XP850 and perfect at idle, perfect at WOT, but pig rich at cruise. Like 11 to 1 ish. Light 4 speed car with 4:30 gears. Timing locked at 33 degrees.

Tried changing air bleeds, P Valves....all for naught. Jetted primary from 84 to 77 and cruise was fine but any "spirited" acceleration on just the primary got dangerously lean.

So carb is now back to box stock config, hoping to fin a fix for my issue. Wondering why the PO blocked the middle emulsion? I'm carb stupid when it involves anything other than a jet change.

Not knowing much I’d say you need T slot restricters. Not sure what you have for emulsion but some of those carbs came with too much emulsion and way too big of a main air bleed.

A bigger air bleed wi start it on the booster sooner. If your MAB is bigger than .026 it’s probably too big. That will get it on the booster sooner and that makes it richer sooner.

 

[TT5.9mag]

Tried changing air bleeds, P Valves....all for naught. Jetted primary from 84 to 77 and cruise was fine but any "spirited" acceleration on just the primary got dangerously lean.

Jet the primary for cruise afr and tune the power valve channel restrictions for wot afr.

 

[Mattax]

Wondering why the PO blocked the middle emulsion?

Out of the box most of these 3 e-hole blocks are over 'emulsified'. In other words the fuel is no longer an emulsion of liquid with little tiney amounts of air but liquid with big bubbles coalescing randomly and unpredictably.

Tried changing air bleeds, P Valves....all for naught.

So maybe the problem isn't fuel.
Or the circuits you're messing with aren't the circuits that need fixin.

but any "spirited" acceleration on just the primary got dangerously lean.

'splain that.
Lean can be dangerous under heavy load. Going leaner under moderate acceleration is correct. (Yea I know this is contrary to what many of us thought)

Timing locked at 33 degrees.

This is likely making your quest more difficult.

 

[Ironmike]

Not knowing much I’d say you need T slot restricters. Not sure what you have for emulsion but some of those carbs came with too much emulsion and way too big of a main air bleed.

A bigger air bleed wi start it on the booster sooner. If your MAB is bigger than .026 it’s probably too big. That will get it on the booster sooner and that makes it richer sooner.

Main bleeds are 34, from the factory.. But now I'm confused. I do know smaller bleeds will pull more fuel (I thought). I need less fuel at cruise.

 

[Ironmike]

Jet the primary for cruise afr and tune the power valve channel restrictions for wot afr.

This is exactly what I was thinking, but how much? I believe my PV restrictors are .062. Factory.

 

[TT5.9mag]

This is exactly what I was thinking, but how much? I believe my PV restrictors are .062. Factory.

Test test test. That is the only way to know.

 

[Ironmike]

Think I'll start with .070.

 

[Newbomb Turk]

Main bleeds are 34, from the factory.. But now I'm confused. I do know smaller bleeds will pull more fuel (I thought). I need less fuel at cruise.

That's way too big for a main air bleed unless you are 1250 CFM and maybe not even then.

You have to get to the point where you are tuning each circuit in order. I always start with the idle circuit and go from there.

As a general rule, two emulsion bleeds is all you need. I have some carbs running one emulsion but that's with annular boosters. And not cheap ones either.

You sound like you are right on the edge of transition from the T slots to the boosters. IMO you'll never get it cleaned up without T slot restrictors AND correcting the MAB.

To that end, when you do get the MAB correct, you will need to look at WOT again. Because it will get fatter upstairs with the smaller MAB.

Which is what happens when the MAB is too big. At low air speeds or throttle opening or however you want to say it, the MAB will ACT exactly like an emulsion bleed. It's adding air to the main well until the air speed is high enough to get the booster flowing.

That HUGE assed MAB is starting the booster too soon. Starting too soon makes it rich and you can't clean it up.

I mean, if the carb was here I'd start with a .026 MAB, T slot restrictors at .068 and and idle feed restrictor of .028 and an idle air bleed of .070 and tune from there.

It's by far quicker and easier to do this on a dyno but it can be done.

EDIT: I forgot to mention you need to unlock the distributor and get a GOOD curve in it. You are absolutely KILLING 20-30 HP so fast your head would spin.

You are killing torque below peak and killing power above peak with that locked out distributor. Plus all that timing at peak torque is an engine killer.

Fix that FIRST.

 

[Mattax]

You may need to redefine your perfromance goals. Its hard to know what you mean by good. I define them as a best power and efficiency for the condition. We can judge this objectively for most steady state conditions.
There's some links in this post that I think will be useful as they provide background to what Newbomb Turk just posted.

Wideband UEGO Air/Fuel Sensor

What are you guys using for affordable Wideband UEGO Air/Fuel Sensor just for tuning purposes

www.forabodiesonly.com

Start over with the idle. Get the throttle to transfer slot relationships so they don't contribute too much or too little at slow idle.
See how it then performs off idle. Then IFR, IAB changes to observe the effect. As noted above, keep the sizes in the known working range.
If the transfer slots are too long then shorten them. Otherwise the next experiments are with the t-slot restrictor.
Keep notes. This is an iterative process, and there will be some dead ends.

Depending on you testing locations for cruise, at some point you can begin to reduce the PMJs to find what steady rpm they start to become a factor. Do NOT test wide open throttle or heavy loads at the same time. For some reason some people want to jump ahead and 'test power' but that should be done seperately. Do that at the track or on a dyno. When it (full power) is setup based on long hard pull (top gear at wide open throttle through peak HP rpm) then it will be right for shorter stabs of the throttle to the floor in lower gears.

I like to save MAB changes for correcting the high rpm WOT fuel ratio. That's it main job. You can tweak it a little to help with initiation, but it has to be in the working range for the jetting or fuel will go lean or richer in the top rpms.

 

[Ironmike]

why on earth does Holley put big main bleeds in? Every carb I've worked with is at least ,030 from the factory. Befuddling!

Also. why put a curve in the dist when I'm almost always above 2700RPM? I mean we're talking about close to 600 on the engine dyno. Probably more now with the upgraded head and intake work.

 

[Newbomb Turk]

You may need to redefine your perfromance goals. Its hard to know what you mean by good. I define them as a best power and efficiency for the condition. We can judge this objectively for most steady state conditions.
There's some links in this post that I think will be useful as they provide background to what Newbomb Turk just posted.

http://[URL]https://www.forabodieso...d-uego-air-fuel-sensor.465546/post-1973010184

[/URL]

Start over with the idle. Get the throttle to transfer slot relationships so they don't contribute too much or too little at slow idle.
See how it then performs off idle. Then IFR, IAB changes to observe the effect. As noted above, keep the sizes in the known working range.
If the transfer slots are too long then shorten them. Otherwise the next experiments are with the t-slot restrictor.
Keep notes. This is an iterative process, and there will be some dead ends.

Depending on you testing locations for cruise, at some point you can begin to reduce the PMJs to find what steady rpm they start to become a factor. Do NOT test wide open throttle or heavy loads at the same time. For some reason some people want to jump ahead and 'test power' but that should be done seperately. Do that at the track or on a dyno. When it (full power) is setup based on long hard pull (top gear at wide open throttle through peak HP rpm) then it will be right for shorter stabs of the throttle to the floor in lower gears.

I like to save MAB changes for correcting the high rpm WOT fuel ratio. That's it main job. You can tweak it a little to help with initiation, but it has to be in the working range for the jetting or fuel will go lean or richer in the top rpms.

LOL…your last statement is what Tuner always says.

I agree with that but when I see a MAB that big I just suck it up and change them to what I like.

Of course, I change the tune up in every new carb I do.

 

[Mattax]

You don't have to. I have no idea of what you're working with or your goals with this vehicle. People certainly have run locked timing and made it work for them. MP setup their race distributors (aka tach drive distributors) for easy starting and to maintain high rpm timing flat or very slightly advancing. (graphed here) They basically accepted idle timing as somewhat unstable because they didn't think it was that important - at least relative to the other two goals (easy starting and top rpm performance).

The reasons to put a curve in the distributor are twofold.
1. It will likely allow the engine to run richer and stronger at idle. The better it runs at idle rpms then the less time for the carb to clear up when throttle is opened.
2. The top end should continue advancing mechanically so as to avoid the retard that comes naturally with most electronic ignitions. (If running dual points then not needed.)
As illustrated in the two videos posted here. lets revisit timing

Mallory Unilite timing issue

The delay is in the electronics themselves such as an msd box or the orange Mopar box Different brands have different delay. Example, pertronix has about a 2 degree delay @ 5,000 rpmMsd has a 4 degree delay @ 5,000 rpm so you can curve the distributor to counter act the delay.Orange Mopar ...

board.moparts.org

Here's a couple guys who have run Stock Eliminator commenting on the subject, GTX John and 92b. What used to be done with dual points no longer applies with electronics even for drag racing. lets revisit timing

If you keep with the locked timing, then the idle will have to be lean. Timing goes hand in hand with conditions in the combustion chamber. Increase the fuel load and it will be denser, higher fuel compression and need less lead time to be converted into pressure to push down the piston in time to do work on the crank. Also more exhaust gases going out the port (more fuel going in) so ought to help in keeping the exhaust moving away.

That doesn't mean it can't be made to work with locked timing on at least some setups. Lots of guys do. if you go that route,at least you'll be aware of how it may be effecting what you need to do with the carb.

A large timing lead at closed throttle can help increase manifold vacuum, which in turn helps the fuel gasify and distribution. There is a point where there is no more gain. With a stick car you can get away with a leaner mix than automatic. With an automatic the engine needs to have power to turn the pump, converter, and gears at idle.

 

[Newbomb Turk]

why on earth does Holley put big main bleeds in? Every carb I've worked with is at least ,030 from the factory. Befuddling!

Also. why put a curve in the dist when I'm almost always above 2700RPM? I mean we're talking about close to 600 on the engine dyno. Probably more now with the upgraded head and intake work.

Because the guys that determine the tune up on these new carbs are smarter than the guys were back in the day. That’s sarcasm.

But that’s what has happened. The physics and science never changed but in the 1990’s everyone forgot everything, ignored the research from the beginning and over emulsified and over bleed EVERYTHING.

That’s why it’s happening.

You NEED a curve because that’s what the engine wants. Most everything that has to operate over a wide range of RPM.

What happens is you end up with way too much timing at peak torque and not enough timing at peak power.

Trust me when I tell you I got embarrassed defending what you are. That’s how I ended up with my distributor machine.

I was a lock it out guy or at least get it all in by 2500.

William Baldwin of Baldwin Carbs called me out in my error. Then he posted a video of what happens when you lock one out.

I was so wrong that I bought my own machine so I stopped jacking up distributors.

Not only do you end up with too much timing at peak torque and not enough timing at peak power but you really don’t know how much timing you actually have unless you set your total at max RPM.

All ignition systems retard with RPM. All of them. And the same part number boxes will not retard the same amount or even at the same RPM.

I have posted several videos of the same thing. It’s real.

You need a curve.

 

[Ironmike]

Well, I did machine a bushing for my MSD distrib that should be around 10 degrees. The 18 that they provide(the least amount), is way too much. I think. I don't know how this thing would idle at 15 degrees initial. Cam is solid roller .668/.668 259/265 .
Might try it. Can't hurt.

 

[Newbomb Turk]

Well, I did machine a bushing for my MSD distrib that should be around 10 degrees. The 18 that they provide(the least amount), is way too much. I think. I don't know how this thing would idle at 15 degrees initial. Cam is solid roller .668/.668 259/265 .
Might try it. Can't hurt.

I would say you are going to need at least 22 initial and 24 would be better.

Then you have to delay the curve until you get up to 1700-1800 and then you probably will be 27-28 at peak torque. After that 1.5-2.0 degrees per 1000 RPM until you get to your maximum RPM.

That’s probably pretty close. Within 2 degrees or so.