Jets & air bleeds

Last year I finally started to fine tune.Started jetting up with plug readings using the azz dyno and time slips.Only getting 4 runs in a day made it a loooooong process.I ended the season with the biggest jets I have which are 99's and its square and still a little lean.My carb guy said to start reducing the air bleed size.
What I would like to know,what is the difference between increasing the jet size VS reducing the air bleed. I can see where I might be able to make small changes due to the DA with air bleeds only.Is that ok,,or should I be making those changes with jeta??

I use the ratio of 1 bleed size = 2 jet sizes..
its close but not perfect.. so if you want to
drop 10 jet sizes you drop 5 bleed sizes

Depends on how efficient the carbs are but we have usually seen closer to one bleed being more in line with moving the jet 3-4 sizes. But your results may vary. My opinion would be don't get to carried away with dropping the hi speed bleed, and we are talking just replacing the high speed bleed here. They also sell larger jets than 99, and not all jets are created equal. You could buy 100, 102, 104, 106, 108 and 110's. But honestly buying a Holley jet and not pinning it who knows

Not uncommon to have jets that are way bigger than needed if the hi speed bleeds are too big and I too was at 99`s w/ .037 hi speed bleeds so I went w/.028 hi`s and brought the jetting down to 84-92 (ft. p/v) and now it rocks. What size are the hi`s now...........Another note; can`t pin holley jets w/any accuracy due to the taper unlike others like maxi jets and maybe BLP which are numbered to size not flow...........

Guess I should ad changing two that pin the same will do little to change the curve. Yes some do have different taper that Holley claims this changes the amount of fuel it flows but it will do little to change the amount of fuel there. Funny how no one else does this, so makes one question how much this taper changes anything. I hear the no use pinning thing all the time, I have pinned every Holley jet from 62-110 and can tell you the only time I have seen the same pin size is in SOME sequentially numbered jets, Most likely why many suggest never bothering to change just one sizes at a time, always go up 2.

I think after a 70 holley jet the hole gets bigger BUT the taper and depth changes therefore the FLOW changes. No bs just facts and holley is all I use and the small changes react as they should...........one holley jet equals roughly a 4% change in flow and if it wasn`t for the holley engineers 50 years ago, none of these other holley "copies" would exist.........

Air bleeds (or correctors) are more about the fuel curve than whether the mixture is rich or not. I wouldn't mess with the bleeds unless you have a pretty good idea that your fuel curve shape needs to be adjusted.

We prefer jets where the numbers actually MEAN something Cannat say I have seen the same results on the dyno going up one size on many holley jets. But all I have to rely on is my experience on the dyno reading AFR numbers and jets. I am not a carb guru for sure.

BTW it if was not for Henry Ford we would not be where we are either. Things progress you either keep up or fall behind. To each their own. Guess we should just keep using those old sand cast metering blocks and porous main body and boosters too

I`ll keep that in mind Andy after the many I`ve fixed w/(don`t touch the bleeds)are awesome just ask around and yes the bleeds are the curve and when the jets are out in left field the CURVE is jacked due sometimes to hi speed bleeds. Again Andy, you spend time in a dyno room(not real world)and I test/tune on the mean streets and most on here are faster and cleaner after I touch the "don`t touch" hi speed bleeds. Al, I usually see results from a two jet or more change and I love the billet pieces and modern touches for sure it`s just the WACKED tunes as YOU`VE admitted that needs help........Forgot; I have two local 8-second street/strip cars that have stock blocks n bowls on em SO they do work just not as light and pretty.......

As the RPM and the boost goes up,so do the AFR's.I'm stll pulling plugs,so easy with a hemi.It's getting into the high 13's with NO speckling.I'm starting to thing that back pressure might be diluting the combustion chamber
At this point I can see the results on the next pass,unfortuatly I have to wait 'till spring to continue being a tuna fish.My next 2 obsticles will be heat & the full exhaust.

The air bleeds, high speed and idle affect the mixing of air and fuel in the carb. I look at the percentage of difference in hole sizes when changing the bleeds, a .027 bleed compared to a .029 bleed is substantial difference in the percentage of the hole sizes. Bigger bleed hole equals more air with less fuel, less hole size equals less air amd more fuel into that circuit The idle circuit bleeds affects the air fuel ratio from idle to W.O.T no mattr wah the RPM I remember a statement in National Dragster that the Pro Stock teams didn't change jets in thier carbs. once they had them dialed in from Denver in the summer to Pomona in the winter, they would and did change the bleeds for each track and weather conditions on a regular basis
Tune off the spark plug and time slip for that day, unless you buy and use a wide ban Once you get the car as good as you can from jetting then try tuning the bleeds IHTHs

AGAIN, What size hi speeds bleeds are in it(em)now...........

Dom,they have .038 in the high bleeds,jets 99 square.Best pass so far had 30* timing.Want to try 28* and see if it picks up.I will change the HSB's and start from there in the spring.
I did install a Racepak logger dash so I can see what's going on.Want to find the limit on pump gas with a few more passes,then overdrive it then see where it will go.At almost 4k LBS,it's a handfull

Are you by chance using E-vacs with them ahead of
the O2 bung.. if so.. change that.. you will get a
bogus A/F reading... also if the bung is near the
exit of the collector.. that will give you a lean
number also

I have never liked how Holley jets are not the same size as the number once you get above a certain size which is around the 80 or so size. I always measure the Holley jets with my drill sizes. Sometime you can go up a number or two and not even change the jet size if you forget that they dont always match the number on them. Ron

Try some 28`s for starters and watch what happens w/the jetting........

So at this point it doesn't matter which way to fatten,be it bleeds or jets??

What do you have for a jetting set... if yours goes
up to 99s now then yes it would matter.. unless you
want to start buying more jets.. I have 2 sets(boxes)
that range from 35(I think) to 99.. I have 2 sets for
when I was running dual 4bbl and when I got my dom
from QF after having them set it up for E-85 I asked
if they could set it up for the jets I have.. they did
so that way I wouldnt have to go buy more.. just something
to think about

That's what I was unsure of.If one changed the AFR differently than the other my jet selection ends at 99.I want to fatten the bleed and take some jet out.Then see how it effects my AFR's.I also put an air temp sensor in the intake to see what the temp is when I hit the heat ceiling.I also wonder how back pressure effects the AFR's.

Evac is capped.O2 should be back far enough in the exhsust pipe.
Collector is 4 inch going into 4inch exhaust reduced to 3.5 In front of the muff When I remove the exhaust,I will need extensions and put an o/2 bung in them.
I Thoght bleeds & jet changes effected the AFR differently

Not sure how it applies to a blown application, but I thought the guideline was the HS bleeds generally end up 26-28 when emulsion is correct...

I would agree with Dom and start with a 28-9 HS bleed. What you have is way to big IMO for the top end on any application especially in a blown application.

What fuel are you using? Each race fuel will have a different stoich reading. For instance what we use in the heads up car is best closer to 12.6. Just saying this may be worth looking into as you may be WAY leaner than you think.

that is how I understand it also, sound's like you need to start dropping the bleed size down, if i remember correctly 26 is where my bleed size is on my dominator, but I would start dropping them down 2 sizes at a time, car should start picking up with the added fuel if it is in fact lean.

Read the second post in the following thread. 37 is way too big for MAB's, try 28's. And the rest of the car/engine/carb info might help.

http://racingfuelsystems.myfunforum.org/viewtopic.php?f=25&t=42

Just throw some 28`s in there and be prepared to POSSIBLY jet down. Read the post Mark posted to grasp the relationship between e-bleeds and hi and low bleeds to see how they SHAPE the curve and how the jet in fuel and booster outlet control it.......Then there`s angle channel sizing etc.

The picture that Tuner included in that thread is a classic. It should be a sticky on here so people understand the difference between bleeds and jets.

That's what I'm trying to find out Andy,bleeds VS jets.Now at .035 and will go .028.
Al,I'm still on pump gas.Would like to find how it goes on pump junk,get it consistant so I can tune the suspension. Caltracs & Vikings on all 4 corners. My 60 are not that good

That appears to be where I end up with smaller jets.

Last pass the plugs were white with NO speckling,I know if I could have fattened it up there was a few MPH to be had.

So that can be done that way and not change AFR's??

You can NEVER fatten it up enuff w/38 hi speed bleeds.........

He is using SV1's for carbs you guys know, right?......And they do not always fall into the same "range" as other carbs do for jetting.....Gots to follow the AFR....Its the only way I was able to start gaining on mine.

Do they differ in their fuel "curve" needs? Cos a 38 bleed is WAY out in left field "generally..........

I tried the basic setup based on the size of the carb....No worky, so lets go with, they are different. Now I could share my setup, but mine is NA and a single carb...Probably totally different, dunno. I am not a carb guy.

I do know that my AFR is right around 11.9/12.0 WOT....And I need to lean it out just a tad more, and then work on my transition. These carbs idle better and cruise better than anything else I have seen, but I still struggle with the transition which is port #5 I think....

You also have to remember, these uncover a lot of throttle really quickly being what they are...I have called and received tuning advice, and I found the best way is to street it and watch the AFR...Trial and error.

Gotcha, never messed w/one and really have no desire to so your advice definitely outshines mine here...........

Not claiming to know a whole lot...I kinda get myself into more trouble than its worth sometimes.

I'm no expert,,,,but I did stay in a Holiday Express once

Dom seems to be right on, Patrick told me to drop the bleeds down and jet as needed. Guess we will see if the jets & bleeds mimick those of a Dominator.I also had an issue breaking the throttle blades open from idle, I believe the 15 inches of vacume at an idle made it hard to come off idle smoothly.After breaking the second "stock" throttle pedal, I installed a lokar pedal.It's better,but not perfect.

Overhead view,,,,,,,,

I gave it ALL I had,,,,,,99's square

The fix.

AGREED...........But I give him and Dragula kudos for tryin to figure em out for sure..........

Atomization, vaporization and distribution will always be best with 4 holes and a booster. If you stumble on an induction combo where distribution falls in a reasonable spread they will run OK, nitrous combos are also not so sensitive as the nitrous tends to even things out. And the nature of a tube discharge requires little more than a kill bleed, no emulsion, so trying to tune it with tons of emulsion makes it a crap shoot. Roll the dice, take a number and put in it, and hope it works...

Mark,I respect your opinion on the style carb.ANY larger carb that I purchased would have served the cause.I had a pair of 750DP's that were way too small.When I was shopping for carbs and I saw the SV1, http://www.prosystemsracing.com/svseries.html,it became SV1 decision.I have read of many guys that switched from SV1;s to dominators ,but I think they just didn't put the time into learning and tuning. I will by hook or by crook!!
I want to get a grip on the tune BEFORE I change pullies and turn the boost up.I am also curious,,,,once the carbs are dialed in,when I increase the airflow through the carbs by spinning the blower more,,,,,will it just feed more or will I have to fatten it up.That question applies to traditional Dominators as well as the Sv1

I would like to add,,,,,I am using STOCK iron heads with a good valve job and parts.Car weights 3850 and has gone a best of a tick under 145 MPH,
Running no hood with the aerodynamics of a brick,I am very happy with the performance of my street cruzer.I reached my goal last year and have reset my goals for this season.Who knows,maybe next winter I will install these old dart twin plug heads and step it up some more. In the present,I am very happy with the performance to date and know I might pick up a 1/2 second this season

https://www.youtube.com/watch?v=0QWqMVgNvzw

I want to get a grip on the tune BEFORE I change pullies and turn the boost up.I am also curious,,,,once the carbs are dialed in,when I increase the airflow through the carbs by spinning the blower more,,,,,will it just feed more or will I have to fatten it up.That question applies to traditional Dominators as well as the Sv1 [/quote]

It should pull more fuel with the greater air
flow... if the fuel is there to begin with

That's what I hope. It also sounds like I can change the bleeds for the wheather & DA conditions.
I think I'm getting a handle on this. I also need to take another 2* of timing out after going out with the same tune on the 1st pass as last season. I want to get out early to taste the same cool air as we ended with last season!!

Put some .014 main air bleeds in it, see what your fuel curve does... Probably need to take out some jet as well...

If you've ever seen a C&S carb, it comes with a kill bleed and a very small MAB. Tube discharge does not need air correction for the curve that you see with a booster. While I'm not a fan of those carbs, C&S is at least smart enough to realize the emulsion need or lack thereof with a tube discharge.

Mark, I have high speed & idle air bleeds.Not even sure if I have a main air bleed

Sorry, missed the response. mains are the HS air bleeds. My post above was serious, with the large single butterflies getting sufficient signal is a serious issue, for a NA engine. With the blower the use for emulsion to stimulate fuel flow at low speeds will probably not be needed. If it were me I would try a small HS bleed, and if the emulsion is threaded plug all but the kill bleed. If it's not threaded and plug them. Then see how the engine responds.

No bleeds in emulsion dept. It spikes lean and mimicks the boost.Have .035 now. will try .028's and see what the logger says,,,,,,,,

Your emulsion is shown on the blocks below. You can have 2 to 5 positions, and any can be plugged, any with restrictions either pressed in, threaded, or drilled in.


[img]http://www.quickfueltechnology.com/images/managed/3circuit.jpg?v=2[/img]

And this confuses me

a/f spikes up & down,not smoooooooth????????????

Exhaust leak allowing fresh air to be sucked into the headers perhaps?

That is the case for the one side,that's why I didn't include it on the graph.I am starting to question backpressure and how to tell when it becomes an issue.A friend wants to remove an o/2 sensor and put a pressure gauge on it and make a test pass Also,what intake manifold air temp will cause no add'l gain???????

It seems to me that one of the blower motors I engine dyno tested made 50 HP less at 190 F MAT(manifold air inlet temps below the blower) compared to 130F MAT, maybe not so much, maybe more Hot air expands a bunch I do remember switching pulleys and going from CA pump swill to 112 octane ras gas and going from 12% under dirve which made 7.0 lbs of boost at 7300 RPM made 924 HP, reversing the pulleys ended up making it have 13% O.D. and 12 lbs of boost at 6500 RPM with a lot hotter MAIT which cause detonation at 6500 RPM making 1027 HP with 25 degrees total timing. The pull on pump gas with less O.D. and boost pressure liked 33 degrees total timing, we treid from 27 to 36 degrees in two degree increments on the pump swill Looking back at those test I should have started the race gas pulls with 20 degrees total timiing, not 25 We treid 28 and it got worse in a big hurry The owner was way happy and it was late in the afternoon so we stopped while the motor still ran On a blower motor I would bet that back pressure is a big No No
One of my old N/A bracket cars picked .9 ET and 9 MPH going from a 2.5 inch exhaust system with the old Corvair turbo type mufflers with a short side exhaust to open headers with no other changes My pump gas Duster with a three inch system picked up .02 ET and .2MPH in the eight mile by removing the exhaust system from the headers flanges back That gain was probally from the weight loss and not back pressure
I know a west coast blown alcholol racer that sees 400+F MAIT at 50 lbs of boost on his deal

Me thinks to try to install some dumpers,open it up and see how she like to BREATH. And you can see the intake air is at 205,,,,,,,,,

Ya when you change overdrive you'll need to re-do your fuel curve, most likely fatten up, I did at least,couple pics when I ran dual 1150's - gas first, then e85(quick fuel kits, love'em)

Oh ya, when I bolt my exhaust on, engine temps go up 20° , plugs foul, stumbles ect.. I know tuned for open exhaust, I have the 3" flow master system under my B-body, hooker comp's.. 1-7/8" into 3"... Had super comps on it (got run off return road & crushed passenger side tubes flat) they were 2" primary into 3.5" - & could tell difference in power just test driving down road, back pressure & roots blower = canned napalm in my opinion