Holley/Demon Carb stumble

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What it sounds like to me and i can feel it in the car, is a slight baug stumble, then its off to the races.
The big fall on its face is not there anymore because i using PRH slower full throttle stomp.
You can here the eng stumble for a fraction of a sec as the front end is all most at full travel. then it gone.
Go back and watch from 3:10 to 3:19 focusing on 3:18 to 3:19 it fall flat then comes back on.
That run shows it the best
 
Also the Proform videos were from under the car. even in the slo mo start there is no pause then raise more.
converter my be a bit tight, and i think it is but.........don't think it is the smoking gun.
 
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I think you’d be able to see the “two stages” of stall on a video of the tac.

Demon air bleeds don’t have numbers on them.
If you don’t know what they are, you have to pin them to find out.
I’m not sure how they’re sold nowadays, but they used to just come as a pkg of blanks that had a .017” pilot hole in them.

That combo, that elevation....... that 850 Demon carb.
That’s really not a very good match.
 
PRH said:
I think you’d be able to see the “two stages” of stall on a video of the tac.

Demon air bleeds don’t have numbers on them.
If you don’t know what they are, you have to pin them to find out.
I’m not sure how they’re sold nowadays, but they used to just come as a pkg of blanks that had a .017” pilot hole in them.

That combo, that elevation....... that 850 Demon carb.
That’s really not a very good match.
Click to expand...

Agree
Agree
and Agree
I think we agreed long a go this carb is just to big.
#1 even on a bigger cubic eng, it's still not right.
#2 it pulls all the way thru the rpm range(butt odometer)Better then the Proform.

I don't have a good selection of pin bits.
So this is the best i can do

High Speeds .029-.030 (factory 31)
Low Speeds .063-.077 (factory 70)
 
If you have a set of torch tip cleaners in your box, you may be able to narrow it down..
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I'm just laying all of this out into one post so it easier to find for right now.
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The idle and main air bleeds in the demon are 8/32"x 1/8" you can buy brass set screws and drill your own. Smaller idle bleeds will fatten up the transfer slot mixture. I run .066 idle bleeds on my car at the track, .070 on the street. To lean on the idle circuit hurts the off idle transition. Next is the pump nozzle, do they immediately shoot fuel when the throttle is moved? If your running pink cams they are to slow. Try a blue cam up front if you have one.
 
Demon Carburetion Air Bleeds 200082

It would appear these now come with a .025” pilot hole now.
Seems kind big.

Not that you can use them, but the smallest Holley bleeds are available as small as .023”.

I guess there’s always the solder option if you really need them smaller.

I doubt this calibration would work at all on your combo, but the Mighty Demon 850 I was using as a dyno mule for motors in the 650-750hp range was:
HSAB 26/26
Jets 86/97

I don’t have notes on the IAB, but I think it was only a few thou smaller than stock....... so like .066-ish.

The fuel curve was pretty good, and it was pretty responsive on bigger cube motors.

Once I settled in on that air bleed/jetting combo, I was able to leave it alone.

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If i just wanted it to run decent.............i would have got a 3310 or 6777 off of ebay and been done with it. I'm greedy! I want more, and i want to learn more even if it cost me money (that I don't have right now). But $20 buck i can swing.
 
Cudafever said:
If i just wanted it to run decent.............i would have got a 3310 or 6777 off of ebay and been done with it. I'm greedy! I want more, and i want to learn more even if it cost me money (that I don't have right now). But $20 buck i can swing.
Click to expand...

Great attitude!
Nothing came easy for me either. I was always too broke to be real effective, but did have invaluable help.
I had to improvise constantly, but the education was priceless! Stay motivated.
 
Found the thread with the metering blocks cutaway
Page 4
Power Valve Selection: The Definitive Answer

So i'm trying to get rid of the pore transaction with a smaller air bleed. Idle air bleed? just rears or all ?

I have a 6.5 Power Valve in and am thinking of going with a 10.5 that i have on hand.

So here is my question. do i plug the PV and find the flat spot?
Do i use vacuum gauge and set it just above my starting line launch rpm or do i watch the vacuum and put a power valve in just above whatever it stumbles at.???
 
Cudafever said:
Found the thread with the metering blocks cutaway
Page 4
Power Valve Selection: The Definitive Answer

So i'm trying to get rid of the pore transaction with a smaller air bleed. Idle air bleed? just rears or all ?

I have a 6.5 Power Valve in and am thinking of going with a 10.5 that i have on hand.

So here is my question. do i plug the PV and find the flat spot?
Do i use vacuum gauge and set it just above my starting line launch rpm or do i watch the vacuum and put a power valve in just above whatever it stumbles at.???
Click to expand...

I’d start by measuring cruise vacuum. Then I’d check that against how much vacuum you pull at starting line RPM under load because you’re foot braking.

Don’t you have billet metering blocks? They won’t have porosity like those junkers (I didn’t look at the link you posted yet, but I suspect that it has pictures of a pair of metering blocks I cut away that Mattax was kind enough to post so everyone could see them...which is why I can call them junkers...because they are).

Any time you have a jet that meters air, going bigger will make the A/F ratio leaner. Any time you have a jet that meters fuel, going bigger will make the A/F ratio richer.

Which bleed you change makes a difference where the change will change the shape of the fuel curve. For example, if you change the main air bleed, you will make the fuel curve at WOT leaner, but you also delay the booster coming on. So if you want to lean out the end of the fuel curve, but you don’t want to delay the booster, you can change an emulsion jet to a larger one lower in the metering block.

Its stuff you have to test.
 
Trouble is IIRC that car never cruises on a highway. LOL :)
My sense is that its worth trying a higher opening power valve.
Reading post 651.
The engine goes flat? as the car launches.
Remind us, rpms are what at launch?
Load must be high as the car has risen. Would be interesting to see the vacuum but its got to be close to atmosphere as the throttle goes to the floor.
@mderoy340 may know and his car launches well.

The tricky thing with the air is going bigger with the bleed or upper e-hole is that it can actually move more fuel at the begining of flow.

In my experience, it has seemed to me when experimenting that even at slow idle, the idle air flow is already in he upper half of its maximum capacity.
I picture it like this. And at launch, if the idle circuit is contributing its got to be close to 100 % of what it can flow.
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If the main circuit is in the start up of flow, then it could be a slighly larger MAB or top e-hole could get fuel delivery moving sooner (richer).
I just don't have a good picture of where the airflow is on the carb during a launch like yours.
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What I've always said, and try to do, is make changes to the Main Air Bleeds to adjust the fuel curve to be flat from mid rpms to redline in top gear (highest loads).
Then change e-bleeds if the begining if the transition or start up of the main circuit seems messed up.
 
I agree to both..
The elephant in the room is the crazy elevation you're running in. IMO this will make it bleed sensitive.
Maybe if we had someone used to running in Denver conditions could elaborate? ( Off to work)
 
Every ono keeps saying change idle air bleed and i keep thinking why??? I need the mains to come on sooner........Got to quit thinking that way. The HSAB is for fuel trim not start of signal:BangHead:
Richer transfer slot is what i'm after and then trim it with the idle mixture screw....I think that's right????

Think i'm going to start with the power valve first.......Besides, i promised a video over the carb and 3 gear rolling stomp.
 
Cudafever said:
Every on keeps saying change idle air bleed and i keep thinking why??? I need the mains to come on sooner........Got to quit thinking that way. The HSAB is for fuel trim not start of signal:BangHead:
Richer transfer slot is what i'm after and then trim it with the idle mixture screw....I think that's right????

Think i'm going to start with the power valve first.......Besides, i promised a video over the carb and 3 gear rolling stomp.
Click to expand...
I don't know if it needs richer t-slots or soon main circuit start up.
BUT.
A big change to the HSAB to change get the mains started earlier/stronger will affect the top of the curve.
Then how does that get fixed?

IF you want to experiment with idle circuit, a smaller IAB should make the idle richer. My experience has been it will affect slow idle mix too. Not always alot but noticible. Others may have different experience on that.
If the IFR is a little too small it will choke off the flow (max out) before the main circuit gets established.
Going to a slightler larger IFR and IAB is the way to keep the AFR about the same but extend its contribution into high air flow.

I'd don't know what I'd do in your shoes. Probably experiment with the upper e-holes first. See what the guys who have experience doing what your doing say.
 
One more question.
I cant get my pee brain around them scales
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Were or what is A and B and I mean, i get that m,o,n is different air bleed sizes and i get that X,Y,Z is the fuel ratio created by the venturi.
But Were is A B C D?
 
I don't have that full page but its referenced the other way.
A and B are bleed locations in the well, what we usually call Emulsion-holes.
D is the air bleed

The small letters are references to the lines.
Line from o to z would be our goal.
Reducing the number of emulsion holes (might have been a tube type arrangement) resulted in late start as shown by dashed line n - b.
 
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