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Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564863
04/10/14 12:45 AM
04/10/14 12:45 AM
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NC, USA
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davenc Offline
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Frankenduster:

Are you sure it is a "Street" Demon and not a "Speed" Demon? From what I saw at the Demon carb website the Street Demon is a AVS knock-off, not a Holley style carb. The Speed Demon description does mention replaceable air bleeds.

Re: Carburetor tuning with a wideband A/F guage. [Re: davenc] #1564864
04/10/14 01:52 AM
04/10/14 01:52 AM
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Granite Bay CA
Kern Dog Offline OP
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Shoot, now I'm going to have to look that up. I bought it almost 10 years ago.

Today while I was changing jets, I saw that what I think is called the Idle Feed Restrictors are UNtapped.
****************************************************************
It appears that I have a Speed Demon. The Demon site also confirmed that the original jetting is 85/93. I currently am at 83/92.

http://www.demoncarbs.com/Tech/SpecCharts.asp

The carb CFM calculator on the Summit Racing site shows that I need a 788 cfm carb for street use and a 963 cfm for racing. This is for a 493 engine with a 6300 rpm max rpm. These are surely guidelines but not absolutes. The ThermoQuad carbs found on the 70s 440s were 850s and I doubt that anyone spun them to 6300 rpms!


Last edited by Frankenduster; 04/10/14 02:11 AM.
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564865
04/10/14 11:45 AM
04/10/14 11:45 AM
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Benton, IL.
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DaveRS23 Offline
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The new Street Demon is similar in architecture to the ThermoQuad and has only been out a couple of years. If you have had your carb for 10 years or so, it won't be one of the new style Street Demons.

IFRs are usually just a drilled orifice, just like the PVCRs. So you either drill and tap them and buy a handful of bleeds. Or you can get some thin wires and if necessary, some small drill bits. Same results either way.

I have a street/strip 499 that pulls to about 6,000. I went from an 850 to a 950 and then to the 1050 Dominator that is on there now. But the Dominator is a chore to tune for the street. If the carb is tuned properly, you will be hard pressed to over-carb a hot 500" Mopar.


Master, again and still
Re: Carburetor tuning with a wideband A/F guage. [Re: DaveRS23] #1564866
04/11/14 05:49 AM
04/11/14 05:49 AM
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Granite Bay CA
Kern Dog Offline OP
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Quote:



I have a street/strip 499 that pulls to about 6,000. I went from an 850 to a 950 and then to the 1050 Dominator that is on there now. But the Dominator is a chore to tune for the street. If the carb is tuned properly, you will be hard pressed to over-carb a hot 500" Mopar.





I read elsewhere that it is suggested to run leaner jetting then enlarge the PVCR to get the richer A/F only when needed. (On demand)
Sounds great, but how do I go about it? Do I drill the passages out in small increments and test drive the car?

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564867
04/11/14 11:42 AM
04/11/14 11:42 AM
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Benton, IL.
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DaveRS23 Offline
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Quote:

Quote:



I have a street/strip 499 that pulls to about 6,000. I went from an 850 to a 950 and then to the 1050 Dominator that is on there now. But the Dominator is a chore to tune for the street. If the carb is tuned properly, you will be hard pressed to over-carb a hot 500" Mopar.





I read elsewhere that it is suggested to run leaner jetting then enlarge the PVCR to get the richer A/F only when needed. (On demand)
Sounds great, but how do I go about it? Do I drill the passages out in small increments and test drive the car?




When your car cruises on the main circuit, I have found that most carbs are too rich there. But most of the carbs I have had have been very close on the WOT mix. So, in order to keep the WOT mix right, when you pull fuel from the mains you need to add it back with the PVCRs.

When doing that, I have also found that the leaner mains will cause the engine to want the extra fuel from the PVCRs sooner, so a quicker opening power valve is necessary to eliminate a hesitation.

As I stated above, on drilled orifices like PVCRs and IFRs, I just use small wires to reduce the flow and small drill bits to enlarge. This is not better than drilling and tapping the orifices for bleeds. It is just quicker, easier and cheaper for me. And gets the same results.

Most of my engines have been comfortable with the cruise in the mid to upper 14s.

Now if your engine cruises on the idle/transition circuits, some hard compromises/choices may have to be made. That is the situation with the Dominator on my Cuda.



Master, again and still
Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564868
04/11/14 07:11 PM
04/11/14 07:11 PM
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Nevada
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dezduster Offline
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Thumper I believe you would be way ahead buying the book Demon carburators. Lots of good info in that book. Not just carburetor related info, timing, plug reading and more.
Also the beliefe that you would go lean after a good exhaust system is installed is not always so. A carburator works on differential pressure if you have less under the carburator / more vacum = more through jets. Think of a carb as a 1.5 psi fuel injection system. Much of what I have learner is due to the aforementioned book. I wish I were capable of recalling all from that book. Its a good read broken into segments that cover each circuit and tunning guides and tricks.

Re: Carburetor tuning with a wideband A/F guage. [Re: dezduster] #1564869
04/11/14 07:23 PM
04/11/14 07:23 PM
Joined: Feb 2010
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Granite Bay CA
Kern Dog Offline OP
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Good points, Dez.
Who is Thumper?

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564870
06/30/14 12:43 AM
06/30/14 12:43 AM
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Granite Bay CA
Kern Dog Offline OP
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While lately I have been concerning myself with the possibility of a camshaft and converter change, I'm still curious about the way this car runs so rich at cruise rpm.
Nothing has changed since the last few posts in this thread, but today I did order a Quick Fuel metering block kit with replaceable bleeds. It seems that since the car runs strong at WOT with the #83 jets but the guage reads rich at cruise with them, I'm going to try using smaller main jets and larger orifices in the PVCR. It was suggested to try using a lower rated PV to get a head start against a WOT lean-out condition (or stumble). I'll certainly try that too.
I also ressurected this thread in direct response to a thread in the General forum about members that do NOT post results after asking for help.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564871
06/30/14 01:38 AM
06/30/14 01:38 AM
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West Palm Beach, Florida
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Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564872
06/30/14 08:48 AM
06/30/14 08:48 AM
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Northern Calyfornua
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Sxrxrnr Offline
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Interesting reading. I have acquired a dual 'Fast' unit for use on my 512 six pack. Have not installed bungs yet, so yet to get seriously into this. Only have shoved sensors up the tail pipes to get a feel.

Was curious about large variations and rich readings on your engine, particularly at cruise.

Could some random misfire,,,example plug wire, leaky valve, dist cap, vacuum leak, carb issue cause this. Certainly a misfire would cause a overly rich reading as it leads to unburned fuel past the sensor.

Could a contaminated o2 sensor cause such possible incorrect or random readings.

I would pull my carpet, or perhaps buy another cable to see what readings are seen on the opposite exhaust side before continuing to beat myself up chasing possible jetting issues,,,so far they don't seem to be improving the answers to your basic concerns.

Doing this proactive troubleshooting by eliminating the possibility or controlling for any of these possible variables could prove helpful to gaining the piece of mind you seek.

On the other hand, I am learning from the input of others and would hate this thread come to an early end.

Re: Carburetor tuning with a wideband A/F guage. [Re: Sxrxrnr] #1564873
07/01/14 01:26 AM
07/01/14 01:26 AM
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Granite Bay CA
Kern Dog Offline OP
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The swing of the guage has been there all along. Since installing the guage I've advanced the cam, tried different valve lash settings, different fuel pumps, header and collector gaskets, different exhaust pipe, spark plugs, etc. Maybe I'll try plugging into the drivers side bung to see what effect it has.

Re: Carburetor tuning with a wideband A/F guage. [Re: rapom] #1564874
10/09/14 02:37 AM
10/09/14 02:37 AM
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Granite Bay CA
Kern Dog Offline OP
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Quote:

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.




I replaced the primary metering block with a "Quick Fuel" unit. The QF has tiny screw it "jets" in the metering block behind the power valve. I used the same #83 jets that I was using for a while. The A/F numbers went a bit richer at cruise. Maybe the QF block flows more fuel?
I posted in the RACE forum but some responses caught me off guard. I was asked if I had annular or downleg boosters. Some mentioned IABs or IFRs. I wish I knew how to respond but once I get beyond jets and power valves, I'm not familiar with much else. I've looked for pictures of the annular and downleg boosters to see how they compare to mine but I can't find any that make sense to me. I don't have many gearheads nearby so I'm having a tough time here. Idle air bleeds? Idle Feed Restrictors?
I bought this Demon in 2003. What I do know is that it is an 850 with Vacuum secondaries and it came with an electric choke. I don't have the actual model number written down but I thought it came with #85 primaries and #92 secondaries. Looking back, the tuning was heading the right way until I added the X pipe and Dynomax mufflers. Those changes sent the A/F numbers almost 2 points richer!

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564875
10/09/14 10:33 AM
10/09/14 10:33 AM
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Indiana
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""I replaced the primary metering block with a "Quick Fuel" unit. The QF has tiny screw it "jets" in the metering block behind the power valve.""

There is a good chance that this block moves more fuel.

These are your PVCR's (Power Valve Channel Restrictors). You can swap these out to add/reduce fuel once the power valve is open. The Main Jets, Power Valve (2 door and 4 door: each door adds more fuel), PVCR's, and the Main Air Bleeds (or High Speed Air Bleeds) all work together. You change one of these and it affects the others and the main circuit. (Note: dont worry about tuning the PVCR's at this time.)

Boosters:
Straight, Downleg, Annular, and the higher end units have replaceable boosters. There may be more but these are the common boosters. I attached a picture showing downleg (bend downward into the carb) on the right and it appears to be an annular (holes around the inside of the barrel) on the left.

The A/F numbers are now 2 points higher after exhaust change. You should always recheck the tuning after changes to the engine. You might have had exhaust leaks prior causing the sensors to be reading wrong. 2 points is a big change.

8295310-th.jpg (307 downloads)

1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Carburetor tuning with a wideband A/F guage. [Re: YO7_A66] #1564876
10/09/14 09:49 PM
10/09/14 09:49 PM
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Granite Bay CA
Kern Dog Offline OP
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Thanks for the picture. I'm going out to look at my Demon carb to see what my boosters look like.
This helps.

Re: Carburetor tuning with a wideband A/F guage. [Re: Kern Dog] #1564877
10/10/14 04:16 AM
10/10/14 04:16 AM
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Try using a video camera to mounted to be able to clearly read the gauge and show how your driving it. It's nice to be able to see the tach and hear the motor in the video clip too. You can watch it at your leisure.

I email video clips to the guy who adjusts my EFI on my '68, he makes adjustments and emails me back a new tune to download and upload into my SCT tuner to download into my factory OBDII ECM.

It was just plane dangerous and scary trying to wind out my carbureted car through the gears while reading the wideband. Video really helps


1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
Re: Carburetor tuning with a wideband A/F guage. [Re: jbc426] #1564878
10/11/14 02:23 AM
10/11/14 02:23 AM
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smyrna,tn
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We just mounted a smaller tach and the A/F gauge
(both temporary) until carb is dialed in (E-85)
above the oil and water to monitor while going down the track

now working on mounting a cam to record the vitals.



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68 "Cummins" Satellite
70 W-2 449 "More Door" Dart
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Re: Carburetor tuning with a wideband A/F guage. [Re: draginmopars] #1564879
10/11/14 10:22 AM
10/11/14 10:22 AM
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Georgia
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Steve Bryant Offline
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On mine, I created a temporary (magnetic) mount in the ashtray and ran the wires through the bulkhead. When I am done with the tuning, I just unwire everything and put the sensor and gauge back in the box.

When I get really close, I take a passenger in the car with a camera so you can see the A/F and hear the car's RPMs. I also call out things like "IDLE" or "WOT" to make it easier to pinpoint the exact number in the recording.

The gauge I have also has a com port I can connect to a computer but since it does not collect RPM's I like videos better.

8297200-AF.jpg (286 downloads)
Re: Carburetor tuning with a wideband A/F guage. [Re: Steve Bryant] #1564880
10/11/14 11:35 AM
10/11/14 11:35 AM
Joined: Oct 2003
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W. Kentucky
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I really like my LM-2, it records to a memory card and can record up to five inputs. Currently all I record is AFR and RPMs. When I was tuning the carb on my 408 I would make a change, drive and record, then down load the file on the computer and view it in LogWorks. LogWorks is the program that comes with the LM-2. I also added notes to the file with all the info on the carb. This way I can go back and look at the logs and see the changes and know what was in the carb at that time.

Re: Carburetor tuning with a wideband A/F guage. [Re: Steve Bryant] #1564881
10/11/14 11:48 AM
10/11/14 11:48 AM
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Benton, IL.
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DaveRS23 Offline
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It's a shame that there is not an easy way to record A/F and RPM and then display in graph form. When you see the info spread out in a graph, it is much more useable. The details and trends become apparent.

The LM-1, though a bit clunky, was the best at this that I have seen. But apparently the newer versions have not worked as well.

For anyone looking to start tuning with a wide band, I would strongly suggest getting a combo with at least A/F and RPM recording ability.


Master, again and still
Re: Carburetor tuning with a wideband A/F guage. [Re: DaveRS23] #1564882
10/11/14 12:46 PM
10/11/14 12:46 PM
Joined: Oct 2003
Posts: 11,678
W. Kentucky
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Quote:

It's a shame that there is not an easy way to record A/F and RPM and then display in graph form. When you see the info spread out in a graph, it is much more useable. The details and trends become apparent.

The LM-1, though a bit clunky, was the best at this that I have seen. But apparently the newer versions have not worked as well.

For anyone looking to start tuning with a wide band, I would strongly suggest getting a combo with at least A/F and RPM recording ability.




My LM-2 has worked great and LogWorks displays the recordings as a chart. If I knew how to take a screen shot with windows 7 or 8 I'd post a graph.

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