Determining Carburator Fuel/Air Mixture, distributor vacuum advance

[Clyde9]

From: Liv42dayOK (Original Message)    
Sent: 10/22/2004 10:51 PM

My fuel/air mixture is very rich.  I have a year old Edelbrock Performer, 750 cfm, non-EGR carb.  The metering to adjust it very easy but, how do I determine what the proper mixture is and how much to change it?  Can I do this myself or do I need to take it to a shop and have them hook it up to some fancy machine?

I know how to read plug residue but, there must be way to determine how much to adjust to get it right (or very close?)the first time.

What else could be causing this?

I have no idea if the valves have ever been done, although I doubt it.

I've also developed a slight miss at speeds over 50mph.  Last trip, it missed 7 times in 28 miles driving at speeds from 45 - 55.  Once hitting 50 it would miss about every 2 to 3 minutes.  The OEM electronic ignition was changed to a points ignition by the PO and I have no idea if it needs servicing.  I plan to change it back to electronic anyway.  I have no knowledge of setting and maintaining points and frankly, I don't want to.  With that change, should I choose a mechanical or vacuum advance distributor? - Sob



From: Jim83Itasca    
Sent: 10/22/2004 11:37 PM

Vacuum on your ignition and ported is preferred.
Next if you will drop in on the Edelbrock web site and look up your carb they have the different settings for rich/lean conditions.
Out of the box i have found the majority pretty close to right on BUT with the conditions we hand them a few adjustments are needed.
#1 is the vacuum (power rod springs) cuz our heavy weight have a much lower vacuum range due to the weight/wind resistance and on & on.
If you don't have a "indexed" vacuum gauge you need one period and heres why, my Rochestor "stock" the power rods start to dump fuel @ 11 inches of vac soooo i have installed 6 inch springs (GM stock) and it runs cleaner and doesn't gurgle at the higher altitudes.
You can also purchase a carb kit that will help you out once you know where your at (fuel/air ratio) wise.
Good luck

Jim



From: HeavyHaulTrucker    
Sent: 10/22/2004 11:40 PM

You might want to check your metering rod adjustment, if it is running rich.  These are all adjustments that you can do yourself.  I am not familiar with the procedure for the E-brock, but on the TQ you just made sure that the T-bar began to rise at the same time as you depress the accelerator.  As for the idle jets, you start with 2 complete turns out -- then you work with one at a time with the engine running and the transmission in Drive.  Turn the idle screw in until the engine begins to run rough, then back it out just until you get the highest idle speed while noting the number of turns you add or subtract; you then do the other jet the same way, but you set it to match the first jet.  I think that this procedure is the same for all of the older carbs.  But hopefully, this will cure your rich burn condition.

As for your miss, do you have a fuel pressure regulator in line?  Is the carb getting 6-1/2 to 7 psi fuel pressure?  Under what conditions was the miss present?  I know that my TQ will miss when it is fuel starved by not having the fuel pressure high enough.  And, of course, not having your mixture set right will make it miss (bog down, too) -- either from not enough fuel for conditions, or from too much fuel (maybe your rich condition is causing this?).

John



From: jddrivfour    
Sent: 10/23/2004 5:00 PM

I am having fuel delivery problems with my 79 440 Chieftain. I now have the "black" carter electric fuel pump and it seems to be not enough. The mechanical one did not work for me. What models of fuel pumps work for the 440?
Thanks JD



From: denison    
Sent: 10/23/2004 5:32 PM

I would choose the type of distributor that came with your 440 - and they will be the easiest kind to find too. They had both vacuum advance and centrifugal advance. The centrifugal advance is vital - or you would have trouble Getting up to 50 mph. The vacuum advance is only going to affect your mpg, not your mixture or any misfiring.
And when you say that it misses, it must be fairly signficant, or you would hardly notice it. If it has a point type ignition system in it now, but was made for an electronic ignition system, I would suspect that you had a mismatch of coil and condenser, or some poor connections at the ignition resistor, that sort of thing. I would head for the original type of ignition system, but with new parts, though the distributor housing itself could be an old one.
Have you tried driving it around the block at night with the engine cover off, to see if there are pretty blue lights sparkling away somewhere?


Do you have any black smoke from the tail pipe? The inside of the pipe will be black anyway, and even sooty a little. I cant tell that my winny is running rich. Yes I smell gasoline in the exhaust, but no more than I have been smelling from carbureted cars since i was a kid. Fuel injected cars these days have a different exhaust smell.
I certainly don't want it to run lean! I don't like replacing exhaust manifolds!



From: Liv42dayOK    
Sent: 10/23/2004 9:54 PM

Dave D,

     By centrifugal, do you mean the same as "mechanical" advance?  It originally had electronic so that's what I want to go back to and use OEM parts.  If I hook the vacuum tube back up to the carb right now, it runs like total crap!  Sputtering, spitting, hardly wanting to run at all... extremely rough, to say the least.  I recall that when I was getting the rig and going over it with the PO, I noticed there was no line from the vacuum advance funnel looking thing (diaphragm housing?) and mentioned it to the PO, he said he removed it because the gas mileage would drop a lot when connected and it ran just fine when not hooked-up.  Which it has, for close to a thousand miles.

The misfiring was imperceptible to my wife sitting next to me; just an occasional "tick".  Except once when the rig slightly bucked.  But, I guess I've developed "Winnie Hearing" because I noticed it the very first time and every time after.

     The black, sooty deposits at the end of the exhaust pipe are actually wet and the gas odor is very, very strong.

     I haven't driven it at night with the dog house off to see if there are sparks anywhere but, that certainly is a unique idea indeed!

     Soooo. to vacuum or not to vacuum.... Jim, Dave?

     I did read over the metering adjustment section for Edelbrock and any info on that which I might need, I know where to get on the website so thanks for telling me about the adjustment guide and also about the metered vacuum gauge.  I had been looking at that as well in the catalog.

     I'm also figuring that I can get these parts from NAPA with the Dodge PNs.  I'll bet they'll total out significantly less than the stuff from Summit.  If NAPA can't get the harness portion, it's available through summit.  I also need to change to the 2 spade, 1 ohm ballast resistor too, yes? - Sob



From: Liv42dayOK    
Sent: 10/24/2004 9:29 PM



From: 73RVDUDE
Sent: 10/24/2004 12:39 PM

Jegs has a Mallory mechanical advance  for $219



From: Liv42dayOK   
Sent: 1/22/2006 10:27 PM

I posted your reply here, John, since it applies to it so well.

Anyway, OK, mechanical advance... vacuum advance... what's the difference?  What's the advantages/disadvantages?  My '74, 440 was OEM equipped with a vacuum advance, correct?  When the vacuum line is removed from the center of the carb, it sucks air... that indicates it's a vacuum advance system?

I got one shot at this, I need to get it right so I can rest assured I've got the right components. - Sob



From: Liv42dayOK    
Sent: 10/24/2004 9:42 PM

I looked in the manual that came with my carb, Jim, and it has the calibration charts and all right in it.  Thanks for mentioning it, I didn't think to look. - Sob



From: Liv42dayOK    
Sent: 10/24/2004 9:49 PM

Can anyone clue me in on the part numbers for the vacuum advance OEM carb and other components I'll need? - Sob



From: HeavyHaulTrucker    
Sent: 10/24/2004 10:10 PM

Sob, I had the opportunity today to actually rebuild an Edlebrock 1405 600 cfm carb on a friend's Ford pickup truck with a 390 -- so now I can speak from experience!

If you ordered this carb, and it was ordered for the 440 in your winnie, then the metering rods probably are not the problem; they are set at the factory, and sealed off with a screw & cap.  You can easily change them if they are the wrong ones, or you want to change performance, but from the factory they should be pre-set.

The idle mixture procedure is exactly as I outlined in my post; the Edlebrock & TQ adjust the same way for the idle mixture circuit.

From my experience today with my buddy's Ford pickup, I would check the fuel pump.  Yes -- that is what I said  .  My buddy was having problems with it apparently flooding out -- it would start fine, but as soon as he gave it gas it would appear to flood out.  So I rebuilt the carb for him, set the floats to the 7/16" float height and 1-1/4" float drop called for, and put it back on the engine; then I set the idle mixture & idle for him and it ran fine.  Two hours later, the truck stalled dead -- it had been the fuel pump all along.  The pump was the old diaphragm type pump, and had a hole in the diaphragm that allowed crankcase pressure to pass through and pressurize the fuel line to the carb.  At idle, it was not severe enough to show any signs -- but when crankcase pressure rose even a little bit, the resulting pressure rise was overcoming the bouyancy of the floats and literally blowing the needles out of their seats for a split second.  This was apparently enough to over-fill the bowl and dump fuel down the carb throat.  He changed out the fuel pump, and it is running fine now.

John



From: Liv42dayOK    
Sent: 10/24/2004 10:28 PM

Well, that really makes it even more of a quandary!  I replaced the fuel pump with an OEM mechanical one about 800 miles ago because the original one has been leaking~!

I knew that the carbs were factory pre-set and usually dialed right in.  I did the carb swap and fuel pump change at the same time so I can't compare any before/after issues.  Although, it didn't seem rich at all over the 300 mile trip I made with the 600cfm carb that was on it when I brought it home.

I did recall one thing though.  When I replaced the manifold, I bought the "kit" which included the intake gaskets.  I noticed that the two center ports of the gaskets were solid, not cut out to match the heads (I believe this is the cross-over port on the intake?).  I called Summit and asked if that was right and they said that the gaskets were made like that so it would produce a little more torque.  Could this be an issue?

If the pump is putting too much fuel in, would I see it in the carb with the doghouse and air cleaner off? - Sob



From: denison    
Sent: 10/25/2004 5:13 AM

I don't think the intake manifold gasket being cut out to match the head versus having the ports blocked is going to make any noticeable difference in torque. Whether your engine has coolant from the water jacket flowing through, or has exhaust gases flowing through, its only useful for the first few minutes of operation, to make the center of the manifold hot enough to help atomize fuel better. For the rest of the day I dont think it would matter, but being slightly cooler below the carb might lower the risk of vapor lock in hot weather.

I have the same mechanical pumps as the 440s have, and I have seen readings on my fuel pressure gauge as high as 10 psi after a brief shutdown in hot weather. The engine started and ran normally, and the pressure dropped back to 7 psi as soon as we were driving along. I find that it begins to lose power and misfire slightly on hills when the pressure is below 2 psi, more like 1 psi. From 3 psi on up it runs the same as far as I can tell. My carb is a Holley, with center hung floats.



From: HeavyHaulTrucker    
Sent: 10/25/2004 11:50 PM

Denison, my TQ functions quite a bit differently at lower fuel pressures.  At 5 (6-1/2 psi) and above on my regulator it runs just fine at all rpm's.  At 4 (5-1/2 psi), it runs fine until I really get on it then it starts to miss.  At 3 (4 psi) it misses at high rpm.  At 2 (2-3/4 psi), it will idle but stalls out within 10 seconds at anything higher.  At 1 (1-1/2 psi), it will not start or run at all.

You're right about the manifold spacer; it is for thermal isolation and has nothing to do with increased torque (unless you are using an Edelbrock manifold, then it might).  The TQ runs best when kept as cool as possible, and requires a degree of isolation because of the phenolic body; that is why the engines that use the TQ all use a manifold-style choke coil.

John



From: HeavyHaulTrucker    
Sent: 10/26/2004 12:01 AM

Sob, I have a suggestion for you.  Since you have replaced the fuel pump, perhaps you should get a fuel pressure regulator like I have.  It is made by Mr. Gasket and is available at Auto Zone for under $20.00.  It is the same style that was recalled, but the new ones have been upgraded to handle the new fuels.

That way, you can dial in the fuel flow to the carb; my thinking is that maybe the new carb requires a higher or lower fuel flow rate than the old one did (the Edlebrock uses larger floats than the TQ and they occupy a larger portion of the bowl, so maybe it requires less?).  Possibly the OEM pump is pumping too high a pressure for the new carb.

You would only see the fuel in the event that the carb is flooding enough for the fuel to pool on the secondary throttle plates; if it wasn't enough to kill the engine, you probably wouldn't see it.  Since yours is running rich, it is probably not enough to see by eye.

John



From: Liv42dayOK    
Sent: 10/26/2004 3:56 AM

Good suggestion, John!

     I guess a fuel pressure gauge would be prudent as well.
- Sob



From: Liv42dayOK   
Sent: 1/22/2006 10:28 PM

From: Derrek    Sent: 10/29/2004 8:28 AM
Mark,

Here is a site with great info on carb tuning and info on how to check your air/fuel ratio using an O2 sensor (available at any parts store) and a multi-tester.

http://www.telusplanet.net/public/gilesij/Volvord/edelbrock_1.htm

I used this info when tuning my carb and found it to be extremely helpful. Hope that helps!

Derrek



From:ssvette1    
Sent: 11/21/2004 10:40 AM

You can always use the old vacuum gauge which I did before my smog check set the idle screws to obtain the highest vacuum reading, you can look it up on the Internet lots of information their, O2 sensor of coarse would be best if you want to hook one up, I adjust my race car by making passes at the track and adjust for the best ET but I think they would look at me funny down there with my motorhome. I also noticed during my smog check that I was running rich until I removed the air cleaner and then it came right in spec. so I put an open element type on, it is louder going down the road but the air/fuel is correct.



From: DaveVa78Chieftain    
Sent: 11/21/2004 9:32 PM

Sob,
1.  Have you ever adjusted or changed the points?  If not set within a certain range they can cause the engine to miss under load or higher RPM.  The contacts burn over time and the dwell setting changes.  The point spring can also weaken resulting in point bounce and missing.  The rubbing block on the points can wear resulting in the point gap getting to small.  Like electronic ignition, points are designed to use a lower voltage during running.  If it is not lowered it will burn out the points prematurely.  The ballast resistor lowers the voltage.  It should only be bypassed when starting the engine.  These are the reasons you need how to work with points.
2.   The OEM distributors for both points and electronic ignition have vacuum and centrifigal (mechanical) advance.  The centrifugal advance works on engine RPM.  At idle the centrifugal advance is 0 degrees.  It should increase to about 13 degrees by 2000 rpm for you situation (points).  An electronic distributor would increase to about 12 degrees by 2500 RPM.  Vacuum advance at idle should be 0 degrees with 0 vacuum at he carb vacuum advance port.  If your hooking it up and it causes the engine to miss fire at idle then you are not connecting it to a vacuum advance port on the carb.  The vacuum advance on the distributor could also have a broken bladder (vacuum leak).  That would cause the engine to miss at idle also.  Vacuum advance works a lot different from centrifugal.  The vacuum advance port is above the throttle plate so at idle and under hard throttle there is very little vacuum developed.  When cruising along on a level road vacuum will be highest therefore vacuum advance will be highest.  I have had a vacuum gauge hooked up to my advance vacuum lately so I can see what the stock setup is doing.  Only increases at light load or cruising situations.
3.  Intermittent missing can be a plug wire breaking down, crack in the distributor cap, weak plug, points if you have them, defective electronic control module (if electronic ignition), or could even be a vacuum leak (lean run condition on 1 or more cylinders).   I recently had the cruise control vacuum circuit develop a leak which caused the number 6 and 7 cylinders to miss (lean run).  The cruise control vacuum tap off point was in the intake runners for those cylinders.  Plug wires can burn underneath the plug boot (hidden) causing a miss.  I have had that happen on mine too.

You really need to convert that ignition back to the stock electronic ignition.

The thermoquad carb has adjustable primary metering rods.  This controls the air/fuel ratio mixture.  I seem to recall the Edlebrock carb has a simular setup.  For thermoquads this was a factory adjustment that was advertised that it should not be changed.  Even rebuild kits say not to change that setting.  I did not read ( I am male afterall) the do not disturb the setting when I rebuilt my Thermoquad.  I have had to play with it to get best performance.  The only way I know of being able to see the effects of adjusting the primary circuit is with an O2 sensor.  On newer vehicles the O2 sensor is used to monitor the air/fuel mixture and auto adjust the mixture to maintain the 14 to 1 ratio.  Our rigs did not come with one so, you would have to weld a sensor fitting into the exhaust pipe near very the head.  Has to be close because the O2 sensor requires a high temperature for operation (600 or so).  What you would be doing is adjusting the primary mixture for a mixture that averages around 14 to 1 over the operating range.  Our carbs do not have a O2 feed back circuit so you can only get an average value over the operating range.  You can either use a voltmeter or one of the after-market O2 sensor gauges to monitor the O2 sensor output.   The idle adjustment circuit (those 2 adjustment screws) is not used above idle so that circuit has nothing to do with the primary circuit adjustment.

Dave



From: HeavyHaulTrucker    
Sent: 11/30/2004 11:08 PM

I have found a neat toy... er, I mean tool... that will mount in the hole where your vacuum gauge goes, and will tell you when your carb's air/ fuel ratio is correct.  It is the Auto Meter 4175 Air/ Fuel Ratio Meter.


The outer black ring is actually a row of colored LED's that light up in sequence.  You have the proper air/ fuel ratio when the LED's in the center scale range light up (green, I think).  No more guesswork, and you have a real-time display of how your engine is running.  You can also use this to monitor your fuel mileage (when it is green, in the proper range, your getting your best mileage -- higher or lower readings should indicate lower gas mileage).

It is available from AutoZone for about $100.00 or less.  There is also a Oxygen Sensor Kit (#2244) available that will allow you to easily add the necessary sensor with a cable that plugs right into the gauge.

John



From: mightybooboo    
Sent: 12/1/2004 9:58 AM

Interesting idea John,heres  some  more   cool gauges.There is a link to his homepage at the bottom to  see his digital readout gauges.Remember to  figure 02 sensor into cost,with autometer  add 100  bucks for their kit.I sure like the idea though.Also autometer gauges tend to  really bounce around,some reviewers didn't  care for them   for  that reason.This guy can modify them to read more accurately.Do we have a spot to add o2 sensors to our rigs where they can reach 600 degrees?This would be a great smog test tool,eh?
BooBoo

    Gadgetseller

    Specializing in precision digital air/fuel gauges in custom colors and "full throttle" modified Autometer and Nordskog air/fuel gauges. Site last updated 11/23/04

Autometer gauges Stock and "full throttle" modified Autometer gauges including new C2 series C2 gauge

Digital gauges Custom digital air/fuel gauges...now in Blue! Blue digital - A perfect match to your AFC.

intellitronix gauge Stock and "full throttle" modified Nordskog A/F gauges

digital voltmeter Other gauges and products



    You can tune any car with an oxygen sensor for better full throttle performance and not use a voltmeter! With one of our digital gauges or "full-throttle" modified air/fuel gauges you will be able to monitor O2 sensor voltage with the accuracy of a voltmeter but without the hassle.

    Many people use the oxygen (O2) sensor voltage readings to tune their car while making adjustments to their fuel mixture with an air/fuel controller (AFC). It's nearly impossible to use an AFC without an air/fuel gauge or voltmeter to monitor your oxygen sensor voltage. The typical air/fuel gauges available today are fine for making adjustments during cruising conditions at partial throttle. These gauges are practically useless at full throttle.

    The car's computer will make fuel trim adjustments while cruising at partial throttle. Any reasonable guess at the correct setting on a fuel controller is fine for highway driving. Tuning your fuel mixture is much more critical at 100% throttle. At full throttle, the car makes no trim adjustments to the fuel mixture and it's up to you to get the fuel controller settings correct.

    During full throttle tuning, a stock Autometer air/fuel gauge will simply appear to "peg" almost full rich and will not move. The resolution of the stock Autometer gauge is not high enough to see the subtle voltage changes that occur while at full throttle. Moving only a couple LED's in either direction at full throttle causes the car's fuel mixture to vary from dangerously lean to very rich.

    Gadgetseller's "full throttle modified" solve this problem. The modified Gauge in useAutometer and Nordskog gauges will allow you to easily see a .02V change in your oxygen sensor voltage without taking your eyes from the road. Click the thumbnail to the right to see a picture of a modified Autometer gauge reading about .90V while running full throttle. Just a quick glance at the gauge lets the driver know the fuel mixture is correct.

    If you would like to learn more about the function and purpose of an air/fuel gauge, we would suggest reading the air/fuel gauge theory. This page explains the relationship between O2 sensor voltage and air/fuel ratio.

     

return home



From: HeavyHaulTrucker    
Sent: 12/1/2004 10:04 PM

Since the A/F Ratio gauge is all LED, I doubt that it would bounce -- no moving parts.  As for a place to put it, it seems to me that you could drill and tap the stock exhaust manifold just outside of the exhaust port to get the desired temp -- those with headers could drill a hold and weld a nut to the header in the same location to thread the sensor into.

John



From: mightybooboo    
Sent: 12/2/2004 12:22 PM

The autometer,while reading voltages,bounces all over the face of the gauge,while still staying mostly in the center of the gauge 'stoich'. (14.7 to 1).It still fluctuates like crazy.Go figure.Lots of the guys in the web search I did on it said it was annoying.Some said it really wasn't that useful as a tuning tool,but these guys were using it to optimize their turbos.I think in our carb setups it would be very useful to keep us out of lean/rich conditions.I wouldnt 'mind having one.Wish it were more 'plug and play',drilling out a manifold isn't something I'm likely to  do, I'm not that big a mechanic to get into that.Now if I need to pull manifold,I could send it to shop,that would work for guys like me.I still like the idea,its a winner.
Very interesting topic,A/F,learned stuff about how fuel injection systems at WOT run rich,and the feedback from the o2 sensor to computer loop doesn't work under WOT,interesting stuff for sure.But you can optimize WOT A/F by using a modified version of the Autometer from  the link I sent.Really cool  stuff.I never even knew such a gauge existed!Thanks John for the A/F gauge topic.
BooBoo



From: mightybooboo    
Sent: 12/2/2004 12:31 PM

You know,kind of a different topic,but you people with your Winnies at home sure have an advantage.I would love to be able to go outside and just piddle with it a bit here and there.As I have it,its a 45 minute drive, don't have all my tools,yada yada yada.Slows down doing little mods as it makes it such a pain in the rear working away from home.Find you need a dremel to make a small cut,you're toast,that sort of thing.Cant wait for the day Winnie lives with us.
BooBoo



From: mightybooboo    
Sent: 12/2/2004 12:34 PM

Another thought,do you Gurus know if the o2 sensor could mount right below the exhaust manifold where it meets the exhaust pipe(drill that pipe?),would that get hot enough at idle,or if you could run it until hot enough and make your adjustments before it cooled back down?
BooBoo