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Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564843
02/01/14 02:12 AM
02/01/14 02:12 AM
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Granite Bay CA
Kern Dog Offline OP
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Yesterday I pulled the MP Chrome ECU and installed the Rev-N-Nator that I bought about a year and a half ago. Back then when I tried it, the engine detonated worse than it did with the Mopar ECU. I had to retard the timing to 29 degrees to get it to stop knocking. That put my initial at 15 and it felt lazy off idle. Since then I have learned how to set the advance curve in this distributor.
I was going to try vacuum advance but the instructions read that their ECU isn't compatible with it. No problem.
Theres more tuning to do to get the A/F readings closer to the ideal. I expected that the thicker head gaskets and lowered compression to cost me some power. I figured the head porting would offset it. As it is now, the car flat out scrams!
It sounds great, it feels great. After all that I have been through in the last 8 months, I would have been satisfied with the same power but with NO detonation. Its a nice plus to have these changes result in MORE power too.

Re: Carburetor tuning with a wideband A/F guage. [Re: YO7_A66] #1564844
02/17/14 04:58 AM
02/17/14 04:58 AM
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Granite Bay CA
Kern Dog Offline OP
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Last week after adding the H pipe to the exhaust, the readings changed again. I have read many times that when headers are installed, the engine often needs bigger jets. I figured that the H pipe would have had a similar effect. Somehow my 40,50,60 mph cruise readings are now really rich again in the 11.0 to 12.0 range. Its almost as if the 02 sensor is lying to me.

Quote:



Idle in D: Low 14's (If you have your strongest vacuum reading, then this is good)
Light Accel: 11.6-13.6 (Rich 2000-3000rpms= Leaner main jet)
40-60mph Cruise: 13.1-14.0 (Try leaning it out a little more to find your lean limit = Leaner main jet)

Leaning out the main jet will lean out your light accel and every reading the rest of the way up the rpm range. Your carb appears to be setup to cruise using the main circuit. Some do and some cruise on the transition into the main circuit. Now that you know, it will make your cruising tuning easier.






I'm going to map the readings as-is again, then I'll reduce the jet sizes again. Oddly, at WOT it has gone into the 14.0 range. Its like the H pipe reversed the fuel curve to where it runs rich at cruise and leans out at WOT.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564845
02/17/14 06:24 AM
02/17/14 06:24 AM
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GTX MATT Offline
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Quote:

Last week after adding the H pipe to the exhaust, the readings changed again. I have read many times that when headers are installed, the engine often needs bigger jets. I figured that the H pipe would have had a similar effect. Somehow my 40,50,60 mph cruise readings are now really rich again in the 11.0 to 12.0 range. Its almost as if the 02 sensor is lying to me.

Quote:



Idle in D: Low 14's (If you have your strongest vacuum reading, then this is good)
Light Accel: 11.6-13.6 (Rich 2000-3000rpms= Leaner main jet)
40-60mph Cruise: 13.1-14.0 (Try leaning it out a little more to find your lean limit = Leaner main jet)

Leaning out the main jet will lean out your light accel and every reading the rest of the way up the rpm range. Your carb appears to be setup to cruise using the main circuit. Some do and some cruise on the transition into the main circuit. Now that you know, it will make your cruising tuning easier.






I'm going to map the readings as-is again, then I'll reduce the jet sizes again. Oddly, at WOT it has gone into the 14.0 range. Its like the H pipe reversed the fuel curve to where it runs rich at cruise and leans out at WOT.




At WOT I would expect it to lean out some after adding the H. I'm not sure why you'd get so rich under normal driving conditions though, but listen to what the AF gauge is telling you.

What carb are you running out of curiosity?


Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
Re: Carburetor tuning with a wideband A/F guage. [Re: GTX MATT] #1564846
02/17/14 04:35 PM
02/17/14 04:35 PM
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Granite Bay CA
Kern Dog Offline OP
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The carb is a Barry Grant 850 Vacuum Secondary. It was electric choke but I disabled it and removed the choke plate.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564847
02/17/14 06:01 PM
02/17/14 06:01 PM
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Northern OH
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Since you have a BG carb you might be able to tune your cruise A/F where you like it with your regular jets. Then tune WOT with your Power Valve jets. A good carb will have replaceable power valve jets which can be changed. You have to remove the Power valve to get to them. Not sure where to buy them cheaply. Or they can be drilled out a little at a time.

Last edited by rapom; 02/17/14 06:04 PM.
Re: Carburetor tuning with a wideband A/F guage. [Re: rapom] #1564848
02/23/14 12:31 AM
02/23/14 12:31 AM
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog Offline OP
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I wrote before that the car was running richer at cruise and light acceleration with the Rev-N-nator box. I should have mentioned that the REV unit requires less timing than any other system. I had backed off the timing 3 degrees from my normal setting to accomodate the REV box. I replaced the #84 primary jets with #83s. The numbers improved some but not enough.
Today I pulled the REV unit and reinstalled the Chrome ECU. I also reset the timing. The numbers improved more but they are not optimal. I now realize that the timing setting had more effect on the Air/Fuel ratio than I expected. I had blamed the REV box for the change in the readings when it was surely due to the change in ignition timing. While I was out today, I didn't have the wife along to map the numbers but I am now running 13.4 or so at WOT. The readings at Cruise seem to jump around and have been hard to pin down. They are rich sometimes (12.0-12.8) and other times they are in the 14.0 range. Maybe the numbers I'm looking for may not be found with the combination of this cam, carburetor and ignition. The car runs hard though. It isn't pinging. I should count my blessings!

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564849
03/31/14 12:01 AM
03/31/14 12:01 AM
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog Offline OP
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Its been over a month and while I've been working on other things, I figured I'd report in again.
I recently added a 3" X pipe system and 3" Dynomax Welded Ultra Flo mufflers. I retained the 2 1/2" tailpipes though. The A/F numbers seem to have stayed about the same. I'm not sure why.....

Re: Carburetor tuning with a wideband A/F guage. [Re: YO7_A66] #1564850
04/08/14 07:03 PM
04/08/14 07:03 PM
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Granite Bay CA
Kern Dog Offline OP
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I just returned from a 950 mile round trip to Los Angeles and back. The Air/Fuel numbers still have me a bit confused. I thought that when a restriction in the exhaust system is removed, the carburetor sometimes needs to be jetted richer. In my case, after installing the 3" pipes and X section, the car runs richer. I was running in the 11.6 to 12.5 range at 70 mph cruise, 2800-3000 rpms. I have already reduced the jets from #86s to #83s before the exhaust work and the numbers were getting closer. After the exhaust work, the numbers went PIG rich!
Member YO7 A66 wrote this:

Quote:

Or, If you wish to lower your main jetting 2-4 sizes and retest your 2000-3500rpm A/F readings again, this might tell us too. If the large change in main jetting does little/nothing in the A/F readings in this rpm range, then this might point to the IFR's being to large which would be causing the rich readings. If the leaner main jetting changes the A/F readings by a point or more, then you know that your main jetting is where you are getting your fuel in the 2000-3500rpm range.

Note: Your main jets may or may not affect your cruising A/F numbers under 3000rpms or so. It just depends on the carb. Some carbs use the transition circuit for cruising and some use the main circuit for cruising.




I'm not familiar with the Idle Feed Restrictors unless they are the thin diaginal slots in the throttle bores. Cab Burge suggested blocking part of the IFRs with wire to see if they are too big for my needs. I need to learn what the IFRs actually are before doing this.

I'm going to lean out the primaries again to see if the numbers move. I'm just surprised that a less restrictive exhaust made the car run richer. I didn't change anything else.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564851
04/08/14 10:35 PM
04/08/14 10:35 PM
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Granite Bay CA
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The confusion continues.
I decided to drop down 2 jet sizes on the primary side from #83s to #81s. The A/F numbers improved slightly but....The car slowed down and actually knocked a little on one run. The numbers at WOT were in the 11.8 to 13.5 range. At cruise it bounced around between 12.0 to 14.6. It really sucks that the numbers have such a wide sweep. Is that normal for it to bounce around so much?
The jet change resulted in less power and one incident of of detonation despite the guage reading richer than the target. This leads me to distrust the guage or doubt the integrity of the carburetor. If I lost power and knocked, I'd think that I leaned it out too much even though the guage says different. I might try my Holley 750 from my 67 Dart to see what numbers I get from that. I wonder if this carburetor is beyond my or anyones ability to tune. These Demon carburetors have a mixed reputation.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564852
04/08/14 11:25 PM
04/08/14 11:25 PM
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California
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i don't know, but that doesn't sound like a happy carburetor...

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564853
04/09/14 12:28 AM
04/09/14 12:28 AM
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It is not normal for the cruise AFR to bounce around so much. Fuel is being pulled (or leaking) from somewhere it should not be coming from under cruise conditions.

Is this a "Mighty Demon" carb? Have you looked at the metering blocks to determine if the Idle Feed Restriction (IFR) is removable (ie a jet with threads)? Are the Power Valve Channel Restrictions (PVCRs) removable?

Do you know the history of the carb? Are all of the gaskets in good condition?

Re: Carburetor tuning with a wideband A/F guage. [Re: davenc] #1564854
04/09/14 03:36 AM
04/09/14 03:36 AM
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Granite Bay CA
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The carb is the "Street" Demon. I've had it since it was new.
Ever since I put this wideband guage in, the numbers have been erratic. My inexperience in these matters led me to believe that the rowdy cam was responsible for that. I have had the carb apart and found it to be clean inside. The gaskets are fresh. I've sprayed carb cleaner at every point of the carb with the engine running and cannot find a vacuum leak anywhere. The metering block has no removeable PVCRs. I am not sure about the Idle feed restrictors. I'm not even sure what they are. I'll have to do a google search on that.
***********************************************************************
I just did a search. If what I saw was correct, the IFRs are a passage in the metering blocks. I gather that some are drilled during the machining process and left that way. Others are threaded so different size jets can be used for additional tuning. I am pretty sure that mine are only drilled.

Last edited by Frankenduster; 04/09/14 04:04 AM.
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564855
04/09/14 10:43 AM
04/09/14 10:43 AM
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Indiana
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YO7_A66 Offline
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Your readings should be fairly smooth on the gauge especially at any cruising speed and up to WOT.
Since your reading has always done this, you might want to check for exhaust leaks around or upstream from where your sensor is mounted.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564856
04/09/14 11:01 AM
04/09/14 11:01 AM
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Indiana
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YO7_A66 Offline
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If you dropped 2 jet sizes and found no A/F improvement, then you may want to to go back to previous jetting and look elsewhere. Dont worry about WOT until you get the Idle, the transition and the cruise A/F correct.
If your metering blocks do not have screw in idle feed restrictors, then i would suggest tapping them or buying replacement blocks that have this feature. If you really want to nail down your transition A/F readings, then you will need to be able to tune this part of the circuit.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564857
04/09/14 11:17 AM
04/09/14 11:17 AM
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Benton, IL.
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If you feel that you have located the IFRs, then as a test you can mike a few small wires like from a stranded 16 guage. And use a small wire in the IFRs to limit the flow. The IFRs are small, so the wire should be small. I would try to stay under .010, if you can find one that small.

Also, make sure that the wide band is calibrated correctly. You dropped the mains and the engine didn't like it, but the wide band did reflect the change, didn't it?

If you want to define when the mains come in, here is a simple way to do that; just tape over the openings under the metering block that feed the boosters. When you come off the slot to the mains the engine will just stop due to lack of fuel. A short test drive and you will know exactly where your main circuit is and when you are or aren't on it.

You do need to know if you are cruising on the mains or on the idle/transition circuit. The taped off boosters will tell you that.


Master, again and still
Re: Carburetor tuning with a wideband A/F guage. [Re: YO7_A66] #1564858
04/09/14 11:41 AM
04/09/14 11:41 AM
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Once you get the gauge to settle down at cruise, you may want to consider "logging" your tuning changes.
When i make tuning changes, i like to write down info so i can review what the A/F did per that change. I like to write down the A/F readings at 30/40/50/60 mph (steady cruise). If you do this, you can reflect on what your tuning change made at different speeds. This will help you to understand where your changes are taking affect.
If you do this, then if you make a 2-4 jet change, then your readings would show you when your mains are affecting your A/F readings.
You will be able to make quicker tuning changes as soon as you find out "when" your mains start influencing your A/F readings. The mains will not come on like a switch, they will gradually start introducing fuel to the engine depending on throttle position. Once you know when the mains start in, and you have a tuning problem before this rpm, then you know to start working on the transition or the idle circuit.
But as mentioned, you need to figure out why the gauge is jumping around. Exhaust leak, clean 12v supply to the A/F module?


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564859
04/09/14 11:51 AM
04/09/14 11:51 AM
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The Pale Blue Dot
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Quote:

I thought that when a restriction in the exhaust system is removed, the carburetor sometimes needs to be jetted richer.
I'm going to lean out the primaries again to see if the numbers move. I'm just surprised that a less restrictive exhaust made the car run richer. I didn't change anything else.......
The jet change resulted in less power and one incident of of detonation despite the gauge reading richer than the target.



Just some thoughts/questions. Did you check backpressure and verify a reduction? A 70 mph cruise should not have a significant change there, unless you had a really bad exhaust before- I've worked on plenty of cars that had bad Cats that would drive fine until you stood on it, then would fall on their face.
and far as the the jet change don't focus on a "target number", give the engine what it wants. You don't have efi, so there are going to be cylinders that run leaner than others, and you are not monitoring each cylinder. I'd suggest you swap back the #83s and check again. If engine is happy, leave them. If not there may be a fuel problem- delivery, poor quality, sucking air, or carb. If the reading are inconsistent there could be a problem with the gauge. HTH, Steve

Re: Carburetor tuning with a wideband A/F guage. [Re: Skeptic] #1564860
04/09/14 04:16 PM
04/09/14 04:16 PM
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Granite Bay CA
Kern Dog Offline OP
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I have been "logging" the readings with the help of the wife and a notebook. The most recent changes were not recorded since she was at work at the time.

"Just some thoughts/questions. Did you check backpressure and verify a reduction? A 70 mph cruise should not have a significant change there, unless you had a really bad exhaust before"

I did not do a backpressure test. I just figured that a 3" X pipe system and the Dynomax Ultra-Flo mufflers would have less restriction than 2 1/2" pipes, an H crossover and Flowmasters.
I can see your point that at cruise the flow and/or HP gains may not be as noticeable.

The fuel pressure is steady. There are no fuel leaks. There are no apparant exhaust leaks. The guage has been jumpy since I installed it. Since then I have tried different octane fuels, timing settings, carb jetting,engine cold, at operating temp. different spark plugs...The guage still bounces around. It never shuts off of gets dim as if the ground wire were loose. It never "flares" like the headlights in an old car with worn wiring.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564861
04/09/14 06:14 PM
04/09/14 06:14 PM
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The Netherlands
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Are you really sure the exhaust is airtight in front and around the O2-sensor?
Have you tried installing the sensor in the other tube for comparison?

I've installed 2 AFR-gauges in my '60-NewYorker with the rollercammed longram intake engine in it.
But the more I try to tune that system, the more I just want to go EFI with that setup.
I've got some clips of the gauges in the '60 on my Youtube channel to view.

Re: Carburetor tuning with a wideband A/F guage. [Re: BigBlockMopar] #1564862
04/09/14 08:04 PM
04/09/14 08:04 PM
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Granite Bay CA
Kern Dog Offline OP
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Quote:

Are you really sure the exhaust is airtight in front and around the O2-sensor?
Have you tried installing the sensor in the other tube for comparison?





I have it in the RH header collector and the gasket isn't leaking as far as I can tell. I have a bung in the other collector but I'm not sure if the wiring is long enough to reach. I'd have to pull the carpet to reroute the whole deal.

*********************************************************************
I went ahead and put the #83 jets back in. The power came back. The A/F numbers went a bit richer but not as much as before. The wide swing of the guage is a bit less than before. With the metering block off, I checked the power valve. The gasket underneath was a bit off center but was not torn. I'm not sure if it was leaking. I used a new power valve and gasket anyway.
The car feels as fast as it was before I installed the #81s. I may just leave it since the engine seems to respond well to a richer setup.

Last edited by Frankenduster; 04/10/14 01:17 AM.
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