Carb tuning

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treyrags
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Re: Carb tuning

Post by treyrags » Fri Feb 16, 2018 11:37 am

Geoff2 wrote:
Fri Feb 16, 2018 4:03 am
What MT said that was correct was that a smaller air bleed starts the the circuit sooner & a larger AB starts the circuit later....& that goes for all carbs, not just Holleys.
And it is drawing a very loooong bow to say that the A/F mixture, once it starts to flow, will always be richer with larger air bleeds; much will depend on the emulsion tube hole positions & their size.
I don't see anywhere in Tuner's statement where it said a larger air bleed ALWAYS results in a richer mixture at the beginning of flow. I can say that all of the combinations I've worked with get richer at the beginning of flow with a larger high-speed air bleed.

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Re: Carb tuning

Post by Geoff2 » Sat Feb 17, 2018 12:23 am

treyrags,
Tuner said: "Smaller ABs make that cct respond richer/sooner...."

Blanket statement, no mention of the word could do, might do, probably etc.

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Re: Carb tuning

Post by Tuner » Sat Feb 17, 2018 1:14 am

Geoff2 wrote:
Sat Feb 17, 2018 12:23 am
treyrags,
Tuner said: "Smaller ABs make that cct respond richer/sooner...."

Blanket statement, no mention of the words could do, might do, probably etc.
I guess in Australia English reading comprehension is different. I most definitely did not say that, in fact I said just the opposite. The quote is attributed to MTENGINES, to which I responded,
Tuner wrote:"This just isn't so with Holley type metering. In fact, it is exactly backwards, the opposite is true. I wish you guys would quit repeating this misinformation. You need to read this https://www.tapatalk.com/groups/racingf ... .html#p118

More bleed air from a larger main air bleed (or high speed bleed, whatever you want to call it) pushes more fuel up the main well through the circuit and out the discharge nozzle. A bigger high speed bleed or larger or more E-bleeds makes it richer at the beginning of flow. Depending on other factors, such as size of main well and nozzle relative to venturi and jet size, a larger high speed bleed may or may not lean the WOT high RPM range.
Tuner wrote:
Tue Feb 13, 2018 4:59 am


MTENGINES wrote:
Tue Feb 13, 2018 1:03 am
tresi wrote:
Mon Feb 12, 2018 12:37 am
I have many book on Holley carbs but none speak of the air bleeds other than the fact that they are there. What would be some good books that will make me at least somewhat functional at tuning air bleeds?
Probably because as society gets dumber, lawsuits go up. So to cover the publisher's butts, they redact any useful information. Because tuning airbleeds and emulsion circuits can ruin an engine. Not saying power valve, main jet timing can't. But it really is best to have someone with a good understanding make those changes.

If you have a basic underswnding of carbs and know how to rebuild one. Just do yourself a favor and trace each circuit, learn how they work and you can come up with the correct assumptions to fine tune them. Otherwise do a search here or on Google. Ask questions. We can help you.

Here is a quickie.
Smaller air bleed makes that circuit respond sooner/richer , larger later/less. S-S, L-L.. you are adjusting how hard the siphon is working by bleeding some off. Or having less bleed off.


Ask any questions you may have and write down in a notebook our responses. Just make sure you make 1 change at a time and log it. Other wise I may suggest pissing in the wind as a hobby.
(EDIT) To respond directly to the statement above in bold red, I re-quoted MTENGINES. Sorry if that confused you.
Tuner wrote:
MTENGINES wrote:
Smaller air bleed makes that circuit respond sooner/richer , larger later/less. S-S, L-L.. you are adjusting how hard the siphon is working by bleeding some off. Or having less bleed off.
This just isn't so with Holley type metering. In fact, it is exactly backwards, the opposite is true. I wish you guys would quit repeating this misinformation. You need to read this https://www.tapatalk.com/groups/racingf ... .html#p118

More bleed air from a larger main air bleed (or high speed bleed, whatever you want to call it) pushes more fuel up the main well through the circuit and out the discharge nozzle. A bigger high speed bleed or larger or more E-bleeds makes it richer at the beginning of flow. Depending on other factors, such as size of main well and nozzle relative to venturi and jet size, a larger high speed bleed may or may not lean the WOT high RPM range.
The bottom line is this .... larger main air bleed, and larger and more E-bleeds, makes Holley type metering richer at part throttle and low-end WOT for the reasons outlined here https://www.tapatalk.com/groups/racingf ... .html#p118

Parse the semantics however you want, but more bleed in the main makes Holley carbs richer on the low end, before they (perhaps) get leaner.

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Re: Carb tuning

Post by MTENGINES » Sat Feb 17, 2018 1:23 pm

tresi wrote:
Tue Feb 13, 2018 2:15 am
MTENGINES wrote:
Tue Feb 13, 2018 1:03 am
tresi wrote:
Mon Feb 12, 2018 12:37 am
I have many book on Holley carbs but none speak of the air bleeds other than the fact that they are there. What would be some good books that will make me at least somewhat functional at tuning air bleeds?
Probably because as society gets dumber, lawsuits go up. So to cover the publisher's butts, they redact any useful information. Because tuning airbleeds and emulsion circuits can ruin an engine. Not saying power valve, main jet timing can't. But it really is best to have someone with a good understanding make those changes.

If you have a basic underswnding of carbs and know how to rebuild one. Just do yourself a favor and trace each circuit, learn how they work and you can come up with the correct assumptions to fine tune them. Otherwise do a search here or on Google. Ask questions. We can help you.

Here is a quickie.
Smaller air bleed makes that circuit respond sooner/richer , larger later/less. S-S, L-L.. you are adjusting how hard the siphon is working by bleeding some off. Or having less bleed off.

Ask any questions you may have and write down in a notebook our responses. Just make sure you make 1 change at a time and log it. Other wise I may suggest pissing in the wind as a hobby.
Is .001 one step? Is .005 a lot or a little? I don't have a question about a certain situation. It's just some that I should have an understanding of and I know a little knlowedge can be worse than none.
It may or may not.. depending on the number of emulsions, size,well size.

Try it, record it and go back.

What is the scenario you want to fix?

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Re: Carb tuning

Post by tresi » Sat Feb 17, 2018 2:47 pm

I'm not currently trying to fix anything except my knee so I can walk and get back working on stuff. I just want to learn before I need to know.

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Re: Carb tuning

Post by Geoff2 » Sun Feb 18, 2018 4:08 am

Tuner,
I sincerely apologise for misquoting you.

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Re: Carb tuning

Post by Krooser » Fri Feb 23, 2018 7:09 pm

tresi wrote:
Sat Feb 17, 2018 2:47 pm
I'm not currently trying to fix anything except my knee so I can walk and get back working on stuff. I just want to learn before I need to know.
Good luck with the knee.... Fortunately it's not as complicated as a Holley carb...
..
Last place in the B-main is better than anyplace in the grandstands...

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Re: Carb tuning

Post by tresi » Fri Feb 23, 2018 11:20 pm

Thanks

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Re: Carb tuning

Post by levisnteeshirt » Fri Feb 23, 2018 11:23 pm

DVs method seems to play out true IMO ,, one size doesn't fit all ,,, restricted carb ? Really high rpm engine ? Carb too big for conventional thinking ?

If you go jacking up emulsion bleed sizes and adding holes , me myself and I have found this to require more jet to offset the added air , in my terms of understanding things ,, that's what I see ,, but hey go ahead , keep adding them and make the bleeds big as hell ,, I love it when I go the opposite direction and I get a better result , the carb owners reaction is great too :shock: :shock: , I do lots of things other people don't do ,,, but I rarely have a disappointed carb owner , so I'll stay with what works for me

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Re: Carb tuning

Post by MadBill » Fri Feb 23, 2018 11:57 pm

In my somewhat limited Holley experience, bigger HSABs lean out the WOT mixture throughout the whole rev range, but progressively more so towards the top end. If the mixture is going rich at high RPM (which is what I see most often) I increase both the HSABs and (slightly) the main jets.
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Re: Carb tuning

Post by fdicrasto » Sun Feb 25, 2018 8:01 pm

I have been chicken to mess with the hi speed air bleeds because of my ignorance as to what will result. I am going back to dyno my 418 sbc and will try but would appreciate an opinion based on what the bsfc's were running on last trip. 0.500 at 5000 and incrementally leaner till 0.405 at 6100 then slowly back richer till 0.465 at 7500. Based on mad bills post i'm wondering if this is a good situation to increase hsab's to even out the difference from mid range wot to hi end wot. Curious as to anyones experience with a situation like this.

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Re: Carb tuning

Post by MadBill » Sun Feb 25, 2018 8:46 pm

B.S.F.C. is not a direct indicator of air/fuel ratio and it should not be 'taken to the bank' as a measure of jet/bleed changes. You must have wide band O2 sensor data, air turbine/fuel flow meter ratio or four/five gas analysis numbers to calculate AFR. [Or more accurately, lambda (λ)]

EDIT: Recognizing that good AFR data may not be available, the B.S.F.C. of an engine with optimally tuned mixture throughout the WOT range typically drops from the start of the pull, reaches a minimum near peak torque, then starts climbing again. If you keep in mind that too lean will raise it just as much as too rich, you could cautiously attempt to iron out the curve by tracking B.S.F.C., but it's a poor, danger-fraught substitute for good mixture data.
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Re: Carb tuning

Post by fdicrasto » Sun Feb 25, 2018 10:28 pm

I don't have the other data available as far as afr's are concerned so I'm kinda stuck with bsfc's, plug reading and hp and tq numbers to confirm good or bad situations. I'll give it a try when i dyno this again and see what air bleed changes do or don't do and get back with the results in month or two.

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Re: Carb tuning

Post by levisnteeshirt » Wed Mar 14, 2018 1:27 am

If the carb Is small for optimum HP , let's say yoù have a strong 383 with a 750, on top it will go fat , it can't get more air and it's drawing the boosters well , HP is going flat, go up on the main bleed .003 and see what it does , , on a dyno look for 2 peaks , it's going flat In the middle, little things you see and work to line out ,

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Re: Carb tuning

Post by n2xlr8n » Wed Mar 14, 2018 3:59 pm

Fantastic info, and very well put. Thank you.

" A larger main air bleed will admit more air to the emulsion system and that can increase or decrease fuel flow to the engine. The size, number and location of the other air holes in the emulsion system, the size of the main well flow area, the size of the nozzle and the specific pressure difference at the moment are the determining factors. "
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