Holley 500 - A/F swing at WOT

[LUCKY13]

I have been running a 500 two barrel on a basic stock engine. The A.F goes richer as RPM climbs. I have done a lot of air bleed tuning with no help and even emmulsion circuit tuning. Nothing has helped.


There seems to be a lot of guys running the 500 two barrel and I was wandering if anyone has seen this same thing, or found a cure for it. It seems to be becuase the carb is really just to big becuase intake vaccum really falls down to almost nothing at WOT. The fuel curve should still be able to be fixed somehow.


Any expeirances/thoughts?


Jess

 

[XPC66]

The vacuum on the venturi tends rise as the throttle plate opens. The manifold vacuum is of little consequence to a carby; it's the speed of the air and resulting reduction in static pressure that causes the increased suck on the jets.

I'd be looking at my venturi amplifeir (or what ever you want to call it). Or yes reducing the barrel sizes

 

[LUCKY13]

Thanks for the reply.



Yes I agree, but the intake vaccuum is a good indicator of how much the engine is pulling on the carb. It seems to be the air velocity being so low that the booster signal is down. I have thought about annular boosters but I dont really want to cut the CFM down on the carb. I have done some modifications to the downleg boosters that came in the carb and it helped a lot, but not enough to cure it. I am running highway gears and the engine doesnt turn many RPM, so on a shift the RPM drops pretty low which the carb looses alot of velocity and needs help.


I was hoped others have been through this and have found a way to cure it. I feel sure the right booster setup may allow the carb to be tuned better and this may be the cure but I am not sure. There may be other things that can be done to help the booster feed better, but I am kinda new to this carb tuning and modding and I am not sure where to go with it.


Jess

 

[LUCKY13]

Well I had hope to see mroe responses from others that have tried this carb.


I did contact some well known carb builds and got a response from two that I had sent E-mail to. It seems that this carb is so bad for having this problem that they where saying that I was doing better than most by achive the close A/F curve threw all the gears that I have. They even wanted to know what I had done to help this so I guess its a hard little carb to get worked out. They did advise against running the annular boosters though because it would cut the cfm back so much it would not be work it, unless it was a 4 cylinder engine or a very stock inline six that didnt turn many RPM. Althought my engine is very stock its not going to be for long and higher RPM performance will be in its future.



I am going to order some more downleg boosters and build me a small rig that can test for there signal. Even though I want know exactly what there signal is I will know if its more or less and how it responds to high or lower air velocity. I dont know if I will be able to get the carb any better than it is but its worth a try. When I order the booster I will also get the tools to change them out with so I can test differnt setups, hopefully it will get me to where I can dial these carbs in for this size engine. Going lean on the shift will cause detination, and running it rich enough to keep it out of the lean area will loose power although not that much. Which such little power to begine with I dont want to leave any on the table if I can help it. They did give me some other idea I will be trying but until I see there results I will just leave it at.


One thing they did warn about and that was cuttingthe choke horn off, they said in no way did I want to do that because it messed the Holley 500 up instead of helping like you see on the four barrel carbs. I guess this is one odd ball carb in many way and needs a differnt aproach than other Holley carbs. I have wandered if the Keith Dortan series 500 does any better, it was suppose to be designed to help against this for the circle track guys. They use bigger engines though and its hard to tell how it would run on a inline without trying it, thats about $400.00 and I dont want to spent it after already buying a new carb.



Jess

 

[MustangSix]

Mixture will vary as the engine load and speed changes and should not stay constant. At WOT under load, you should be rich, maybe as much as 10:1 depending on the engine. Most engines need to be in the vicinity of 11 to 11.5 at full throttle. At cruise under high vacuum it should be near stoichiometric at around 14:1. Off the throttle and decellerating it could go off the chart lean.

Your vacuum should go to near nothing at WOT and the mixture should get rich at full throttle. My question would be "how rich?". A narrow band sensor will tell you rich or lean, but not how much. A wideband sensor can tell you specific mixtures.

The Holley has three circuits: idle, main, and power. Idle mix is adjustable thru the needles, main is set with jetting, and power is controlled by the power valve and varies with vacuum.

The PV will kick in and add extra fuel at low vacuum. You can tune when the PV activates by selecting one with a different vacuum rating. The number on the PV corresponds to the vacuum it will begin to open.

If you are going too rich at low vacuum, try a PV with a lower number to delay activation.

If the issue is AF ratio going too rich at high rpm, you probably should look at the main jets. What is your current jet size?

 

[wsa111]

Jess, if you have the 4412-500 you are way too rich on these small engines.
At WOT for best power you want 12.8-13.1 AF ratio.
Put 68 main jets in.

Get the power restriction orifices from .061 to .055. No your carb does not have the removable orifices like mine has, so i can fine tune the power restriction channel to what i need.
Reduce the idle orifice in the metering block also to .0295"
Use a 8.5 power valve to cover up a lean hole at part throttle.
I have done these mods with the help of an innovate wide band a/f tester.
My cruising a/f is 14.7 & WOT is 12.9. Bill

 

[kirkallen143]

This is what helped me the most with my holley. I have the 350cfm now and have tried the 500cfm.

Yes get your IFR's (idel feed restrictors) down to about 0.028" to 0.029".
IF you can, enlarge your IAB's (idle air bleeds) to 0.075" and you should be out 1 full turn on your air/fuel mixture screws with these settings.

You could open up your HSAB's (high speed air bleeds) a tad to move the fuel curve later in the rpm range. Stock they are 0.034".

Like Bill said, use the 8.5 PV and down size the pvcr's (power valve channel restrictors) to 0.055". Stock for the 500cfm I believe they are 0.0625". You can tap them for bleeds (#6-32 thread) or use the wire trick (bend sized wire in a U shape and insert the ends into the pvcr's) to reduce their size. Of course with the wire trick you will need to find the area of the pvcr and calculate the area of sized wire needed to reduce to your new specifications.

I ended up buying the QuickFuel billet metering block with adjustable bleeds (changed jet sizes so many times in the stock one that I ended up stripping out the threads) and that was on of the best $60.00 I spent in a long time.

Let us know.

Kirk

 

[kirkallen143]

Lucky13,

I have been reading your post over at the Innovative forum (I am not able to post over there for some reason, even though I am registered).

My 500cfm main body does not have the 3rd hole above the t-slot you are talking about. And like they say try plugging it an see what happens.

You have done just as many changes/combinations to that carb as I have done to mine trying to get the optimal setting for all circuits (idle, cruise. and WOT). I have the Ford 200 with the stock head, yet it is turbocharged. You make one change and it seem to change something else. All I can give you is suggestions and what I have current setting on mine.

I was chasing the same lean transition you have spoken of at off-idle for almost a year. Everything I did (from small IAB's to large IFR's and combinations of the two) and nothing seemed to work properly. My motor is basically stock, w/ a 0.040" overbore and direct mount 2-barrel to the mildly worked stock head (3 angle, unshrouding, port/polish, over-sized valves), and stock cam. To make a long story short, I ended up drilling two 0.094" holes in my throttle blades and it was like night and day. No more lean transition btw idle and cruise, light-load/cruise and acceleration/heavy load was up to par, and WOT was where it needed to be.

My vacuum at idle is @ 20"Hg
ifr's--0.028"
iab's--0.075"
pvcr's--0.060"
pv--8.5
main jets--#66
hsab's--0.034"
squirter--0.028"
pump cam--orange on #1 slot
fuel level--slight drip from site hole at idle
needle and seat--.120" with spring loaded needle and float
emulsion holes(4 on each side)--all 0.028", with top hole plugged, did this because it was above the fuel level mark
And, two 0.094" holes drilled in throttle blades closest side to t-slots.

Keep us posted on your progress,

Kirk

 

[LUCKY13]

Thanks guys for all the replys and thoughts.


My carb is fully ajustable and I do have the Innovate WB system on my car.


I have done so many mods trying to cure this thing I have went to far with some of them and now am waiting on parts to undo, and go diff directions with some of them.


I did some booster mods that was working and taking me in the right direcction on some of the problems, but then I went to far and now my mains went from not being able to get them to start until high RPM, to being able to make them start just off idle if I want.

The problem is I cant get them to come in at the right spot at all light loads ( like 60 MPH cruize, compaired to 40 MPH cruize and lightly incressing throttle to pull a small grade).

I believe someone meantioned using the PV to get this lean spot. I have asked about this over at the Innovate forum with no awnser.

My question was, can you use the PV to richin up the mid throttle without having the mains come in? I have learned very well how to control my mains on this carb, although as I said I am waiting on some booster tools and a arangment of different boosters and feed tubes before I can deside how to set them up.


The swinging A/F problem is at WOT and I have found many ways to address it, but none with a total cure. I do believe the main problem is the intake design, and the carb being the size it is compaired to my engines needs. IT will level out throught the first gear pull, but when I shift it drops from 12.5 to 14.0 on the A/F. Then as the RPM climbs it returns to the 12.5 at about 4000 RPM and holds it until redline ( which is only about 5200). Then when I shift third it does the same thing again, drops from 12.5 to 14.0 until RPM climbs again.


I have done some testing with the emmulsion circuit and was even able to make it go the other direction on the A/F. But right now I have my main circuit so sensitive that I can raise float level just a tick to high and the mains will start feeding setting at a idle.

A new metering block, with other new stuff will be here soon and I will start over and try work this out. The engine really likes 12.8 at WOT and if I can nail it down there through the RPM the timing can be set better and the performance climbs a noticable amount when I hit the right combo of fuel & advance.

I have learned so much I hate to put the carb down and go the other direction ( EFI system) but with this inline six it may be the best bet for me. I do plan to go with a Turbo later, but I want to do with affordable setups that others could follow and not have to go spending for EFI and all the high dollar goodies that most use. I have built many turbo setups over the years and infact use to own a performance shop here local until I was dissabled and closed it. I have mostly built Big Block & 4cly turbo cars and this inline six has its own personality for sure.



For now I think I will wait until I get my carb tools and parts and try to work with what I have. One other problem it seem we found is accel pump pull over that may be causing some of the going rich at higher RPM. Although I am not sure if I would call it that, it may be that it is to lean at low RPM ( WOT) or a combonation of the two. When I was able to make it go leaner as RPM climbs I felt with the right metering and booster setup it could be fixed, but until I get my parts I am not sure. Like others have stated, when you get one part cured it effects a nother and will create another problem. I have not found the right blend to work with this yet and will soon go through a lot more testing. I have the carb in such a state now that its pretty much wacked and no tuning will help.


My next aproach will be with a set of very responsive boosters, but with delayed timing on the mains, then have the PV valve open around 8.5 or even 10.5 if I can find one. I have a felling the biggest cure is going to come from within the metering block with things like main well size and taper. JB weld and some experimenting may find a optimal setup which is something I have not tried yet. The carb becomes one big puzzle full of comprimizes when you start going this deep and the cross over effect from one circuit to the other is something hard to follow.



All thought and ideas are welcome. I have simply jumped into this head first and A*&$#^ deep. I am sure there will, or can be, many ways to approach these problems so any new direction can be something explored that may add to the learning experiance. Although my poor engine really wishes i would get this figured out, its a good think I have a backup.


Jess

 

[kirkallen143]

You talk about shifting and your AFR going to 14.0 then steadys down to 12.5 through all gears, I think a larger pump shot would take care of that or fine tuning the pump cam. Your AFR is leaning out because you are lifting up on the pedal when you shift.

I had the same experience when you talk about the PV and changing to a different one. I my case I was getting too rich at relative high vacuum levels (light cruise / normal shifting) and tried a lower numbered PV from 10.5 to an 8.5 and it cleaned that range up real nice. I tried a 6.5, but didn't have enough fuel and running a little too lean for my standards. With the 8.5 I was still a little rich at 11.0, so I downsized the pvcr's from 0.060" to 0.052" to clean it up even further. I have not tried this yet due to a stripped float bowl screw I just encountered.

I will let you know the outcome once I fix the float bowl thread. I also want to check and make sure the pvcr's are not too small either. At WOT w/ 25% meth/75% water injection I was at 10.5 to 11.0 AFR with the 0.060" pvcr's. We will see what the 0.052" do.

So now my current specs are as follows:

Jets--#66
PV--8.5
IAB--.075"
HSAB--.034"
Squirter--.028
IFR--.028"
pvcr--.052
Orange pump cam #1 slot
.120" needle and seat
.094" hole drilled in each throttle blade
Level fuel with sight plug (small drip)
Top emulsion hole plugged, other 6 are .028"

I believe once you get you venturi size down via the new boosters, that will solve alot of your problems. Like I said before, I could never get the 500 to work correctly for me either (well, with what I knew back then).
I might even try the MotorCraft 2100 that I have like you did.

Kirk

 

[THE FRENCHTOWN FLYER]

The problem is caused by the harmonic resonance an even-firing six sets up that creates havoc in the Holley fuel bowl(s) at high RPM. I can't betray the trust of the people who clued me into this problem by offering a solution because some of them are using it to gain a competitive edge, but if you think about you will come up with your own solution. Good luck.