Holley/Demon Carb stumble

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It's hard to see in the video, but it looks to me like your squirters are too small. IOW's...the pump shot is way too long. It looks like the booster has taken over and the pump shot is still going.

Also, it may be my new glasses and old eyes, but I thought I saw several times where fuel came out of the squirters without the throttle moving.

There are little brass needles that are chrome plated that go under the nozzle. If those aren't in there, you can get a siphon going and pull fuel out of the nozzle.

Just what I saw.
 
:lol:Nope not your new glass or old eyes Stupped Gopro glitching. (sound and video off:realcrazy:)
I'm going to have to make a new video with the current set up.
 
I really and truly think it has to do with the timing of the rear transfer slot and the ventures. but have now way of proving...let alone fix it.
The length of the restriction is a factor(at least it is with jets).
It is, but not enough to make a huge difference.
Just something to be aware of when changing types of restrictoions.
If its .033 and short, and then you drill your own through longer section, then maybe .035 will create about the same restriction.

After i turn in the idle mixture screws in about half of a turn(around 3/4 to 1 turn out) it idle just fine and there is no super strong exhaust smell at idle, like there was last night.
so i think i'm ok with with that....for now.
On a four corner idle, you've double the flow.
If there is decent manifold vacuum in gear, will need less fuel through each idle mix screw than when using a two corner, everything else the same.

22 31 and a 33
Can't mix and match, unless maybe you're someone Braswell and setting up for a very specific narrow range.
Go with what works. Its damn hard to get consistant fuel when there's too much air in the fuel.
Two holes around .026 - .028 or Three hole around .021 and even that is going to require more experimentation.
You need to start with a stable starting point.

I'm really beginning to think the stumble is a RICH stumble, not Lean stumble. when i whack it to the floor, in gear, if i don't hold some throttle after the full throttle stomp it will die. Then i have to hold the throttle part of the way open to restart.
Reasonable conclusion. It takes time to recover.

I wasn't able to drive it today but the stumble is still there. whack the throttle in neutral, primaries only no problem. To the floor and stumble. when completely heat soaked stumble goes away. In gear, in 3d gear stomp and stumble.
A little confused here.
It sounds like what you saying is when the engine is warmed up, you tested to the floor with the primaries disconnected???? Throttle braking?? or launching it??
I say warmed up 'cause heat soaked is what when the engine block is pretty much as hot as it will get after a couple hours of driving. It take a lot of load. Generally you don't get turned quick enough at the strip to run a fully heat soaked engine. Its one reason a little quicker advance curve can be effectively used in the 1/4 mile. Cylinders are little bit cooler than circle track or hill climber engine will be run at.

Maybe i should point the Gopro at the secondary venturi and see what the fuel pattern look like.....
can't do this while i'm driving, but in neutral.
Sorry just grasping at straw.

I think you were on the right path testing but jumped ahead.
a. Set fuel levels where they should be. dribble on standard site plugs, and mid window on the big window bowls.
They can be adjusted for a some fine trimming but for now leave them alone.
b. Get the primary transfer working with no accelerator pump. Open the primaries as slow as possible to reduce the role of pump contribution and there should be no hesitation or flat spot. If it it passes in neutral, then do it driving. As slow as possible from stops.
c. Check the primary transfer under load. Should be able to accelerate or drive up moderate sloped hills at 25 - 40 mps without it dying.
^^^These are the checks and tests for the initial throttle position, idle feed restrictions, and idle air bleeds.

Then go check and adjust the primary main circuit. As above, test for steady conditions first.
Assuming the MAB and e-holes are now ball park...
a. Drive it steady at 50, 60, 70 mph whatever it is to be sure fueling is mostly from the venturis.
b. If you have safe place to test, go leaner on the primary main jets until the engine revs and wants to die - it may even die.
Slow down, restart and take it back to rejet up.
^^^^^^Now the primaries are ball park - at least for mid rpms.

With these idle - transfer and boosters established at steady conditions. Then use the accel pump to cover whats needed with rapid throttle openings.
(Remember the jetting found was for cruising only. Not test the power valve channel restrictions, so may want to jet richer yet on track to start on the safe side.)

Once you feel good about the primaries being in the ballpark, then reconnect the secondaries.
The secondary IFR and IAB, and throttle position are all things to adjust that will effect the secondary fueling when opening.
The secondary MAB and e-holes will effect the secondary booster start up.

Remember the MABs effect the slope of the AFR curve. They also can encourage or discourage the booster startup. Sometimes larger MAB will encourage startup. This is one of the things that some people find frustating. It's not a simple cause and effect.

You've tried these high emulsion 'modern' setups. My suggestion is exorsize that demon by starting with an old school based line like 'Tuner' and 'jmarkaudio' have posted in those links, as well in Speedtalk, the Innovate foum, and a few other places. They're both real people with lots and lots of real carburetor testing and experience. Tuner has worked on more mopars and street motors. Mark has carb shoot championship to his name. One thing you'll notice is they not trying to sell a bunch of parts or magic answers. Dom's another guy you can work with.

I started this post by saying can't mix and match,
By that I meant if someone suggests a MAB, e-hole, jet positions and sizing - then that's a package. They all relate.
We can take a small IFR and a small IAB and get the same fueling at idle as a larger IFR and larger IAB. The difference will be how they continue to carry fuel through the top of the transition. So if someone says they have had success using an IFR, IAB and a transition slot restriction, we can't take the IFR/IAB and expect it to work without the transfers restrictor.

Hope this makes sense and is of some help.
 
Lots to grasp here and Thank you!!
First for the confusion.
I have a electric water pump that turns on at 160 degrees, and a electric fans that turn on around 190 and off at 180 degrees.
When my electric fan has turn on and off a couple of time. i start my testing(in garage testing)
That is what i did yesterday and do all the time. I Will not pull up to the starting line until my cooling fan has turn on a couple of times.
No secondary linkage removed just wacking the throttle too, the point of secondary opening, or to the floor.
I have changed to a smaller main body, i have replaced a questionable base plate. Changes squirter from 31 up to 37s with no change(stumbles at the track, change a squirter size up......Problem goes away or at least manageable for the rest of the race. Next race same story, stumble, bigger squirters, fixed. for the rest of the race.)<-------------Heat Sook explanation.

Like i said on a earlier post the only time this stumble completely gone a way was when it was doing the lean popping.

After it is heat sooked or maybe i should just say it gets warm enough that i doesnt stumble in Neutral. then i do a full throttle stomp in 3 gear, so i don't drive thru the garage, and my brake will hold me in place.

If that is still confusing, Please tell me were, and i will add more detail to help.
timing is 22 and 38 all in

Now to finish reading the rest of you post.:thumbsup:
 
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I’ll make one comment which may or not prove to be relevant for your situation.

With regards to doing your testing in the garage in third gear.......
This might get you close, but doesn’t actually simulate the dynamic condition that occurs on the track.
As such, I wouldn’t concentrate on the loading up after a 3rd gear whomp until after I knew there was still an issue, with the car actually driving off the line.
At the track, you floor it, the car moves, g forces act on the fuel in the bowls, which changes the effective level in the bowls...... which impacts how the main circuits respond.

And, at the track..... you don’t whomp it, then let off immediately.
If there are no ill affects at the track with a certain carb calibration...... I wouldn’t care one bit if it loaded during a “static” whomp.

I also suspect that some modulation of how fast the pedal is pushed to the floor could show very positive results.
 
We can take a small IFR and a small IAB and get the same fueling at idle as a larger IFR and larger IAB. The difference will be how they continue to carry fuel through the top of the transition. So if someone says they have had success using an IFR, IAB and a transition slot restriction, we can't take the IFR/IAB and expect it to work without the transfers restrictor.

Hope this makes sense and is of some help.

So the IFR is on the top or bottom, of the idle chanel, In the metering block. IAB is in the main body next to venturi or the inner air jets,... Where is the "Transfer Restrictor".
 
When added, its usually in the main body.
IMO, reserve that for last resort, when IFR/IAB can't provide the restriction alone.
 
K
so it would be something like the P.V. restrictor/ Protector that's in the modern main bodys.
 
WRT what @PRH was saying, you might find it interesting to compare with double pumper filmed on a dyno.
See Ryan Brown's first video here.
Ryan Brown Performance
He also has older video posted Video
I'm not sure how much he's doing now, but was certainly pretty good about sharing when video was just getting to the point it could be useful and posted on the internet. High speed film was (prob still is) just out of the question for most mortals but video has gotten pretty good.
 
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K
so it would be something like the P.V. restrictor/ Protector that's in the modern main bodys.
Its just a threaded set screw in the passage to the transfer slots.
They're something of a crutch. We're adding another restriction to the transfer slot - which itself is restriction.
The second restriction will only be effective if its about the same size as the first. If its too big, its like no restriction and visaversa.
But the slot itself is variable restriction - only portion of the slot below the throttle blade is restricting the fluid into the intake. The portion above the throttle blade is a variable air bleed.
So there are lots of good reasons leave that technique as a last resort.
 
That said, if you're working with someone who has done a few BG Might demon 850s, and they say the throttle slots are long and they've found a good combos are around x IFR, y IAB and use z TSR, then go with it 'cause its a part of the package.
 
Yeah im continuing on with this package but it far from a matched package. The Demon metering block is the odd man out at this point, and need to buy some metering block that work with a Proform main and base. And i think i'm going too.
The problem is i can buy a standard set of primary 3310s........(gamble with porosity)Or a billet blocks that i can put a 3310 tune into??????
 
Video
this video was kinda cool.
Video Showing what goes on inside the float bowl during a dyno pull
 
????? can you elaborate a little bit more?
This is not may issues but curious.
 
Yeah im continuing on with this package but it far from a matched package. The Demon metering block is the odd man out at this point, and need to buy some metering block that work with a Proform main and base. And i think i'm going too.
The problem is i can buy a standard set of primary 3310s........(gamble with porosity)Or a billet blocks that i can put a 3310 tune into??????


Why do you want a 3310 tune? You can buy some ProForm blocks for cheap. Use a simple two emulsion set up with the IFR's in the low position and tune from there. It would be much more simple than what you are doing.

My cousin almost bought a Demon carb at a swap meet last winter. Fortunately he called me before he did.

I found him a used ProForm 750 for 450 bucks. Cleaned up the tune up by using just two emulsion holes, opened up the power valve channel restrictors by about .010 and put is some T slot restrictors.

Now he is golden. He can make small changes and see it on the plugs. Probably needs to do a bit of tweaking with pump cams and squirters, but he's 99% of the way home.

The point is there is no reason to reinvent the wheel.

I've never been a fan of the 3310 for anything. I'm certainly in the minority but I've done enough dyno work to know they ain't for me.
 
The problem is that the proform metering blocks showed the IFR in the top......Made me gun shy.... already have that with the demon.
High side IFR.PNG
 
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I’m not a well known carb guru, and don’t have nearly the experience people like Mark W have.
That being said, I’ve never bothered messing with the idle circuit to cure a “bog” situation that occurs when going from idle/just off idle to WOT in a tenth of a second.
Maybe I’m missing the boat, or maybe I’m just lucky.

Think of the countless QFT carbs, among others, who are enjoying bog-free operation out of their foot brake cars that still have the IFR in the upper location.

All the messing around with the slots and IFR location seems like it comes into play more when trying to sort out “drivability” problems.

My “good” carb is a CFS built annular booster old school Holley 850 I had done in 1990.
It’s a great foot brake bracket race carb, but it’s pretty rich at low speed part throttle operation, so..... as it sits it wouldn’t be a great street carb.

But, I have other carbs that work fine on the street.
 
I’m not a well known carb guru, and don’t have nearly the experience people like Mark W have.
That being said, I’ve never bothered messing with the idle circuit to cure a “bog” situation that occurs when going from idle/just off idle to WOT in a tenth of a second.
Maybe I’m missing the boat, or maybe I’m just lucky.

Think of the countless QFT carbs, among others, who are enjoying bog-free operation out of their foot brake cars that still have the IFR in the upper location.

All the messing around with the slots and IFR location seems like it comes into play more when trying to sort out “drivability” problems.

My “good” carb is a CFS built annular booster old school Holley 850 I had done in 1990.
It’s a great foot brake bracket race carb, but it’s pretty rich at low speed part throttle operation, so..... as it sits it wouldn’t be a great street carb.

But, I have other carbs that work fine on the street.

I don't know, maybe i just being paranoid or stubone or some thing.
I know YR has/had the high position on his carb and tried to configure it to the low slot and and is his word It hated it!

And then if i do pull the lever and just by the proform to match all the rest of my proforms.......I still have 3 choices........The Race Calibrated one?????????
Search Results for Proform metering blocks
 
If I were going to buy Proform metering blocks....... I’d buy whichever ones come installed on the complete carb that uses the body you bought.

I currently have 3 carbs with the IFR in the high position....... but I’ve only run one of them........my built-from-parts HP950.
That carb works fine.

The other two are my built-from-parts HP750, and a BG Silver Claw 750 someone gave to me....... and I haven’t gotten around to trying them.
 
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WOW! 15 paces to get rid of a stumble thats more than likely caused by the converter being f--d up or too tight!
 
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