Holley/Demon Carb stumble

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jetted it up yesterday. 82/90. thought it would be too much. but after adj the idle mixture screws, it ran the same.
snap the throttle in neutral and no sign of stumble. Put it in gear (3d) and wack the throttle no stumble. Stall a little and wack.......stumble.
Take it out on the road, stumbles from idle, stumbles at 2200 rpm launch.

Got my "Demon Squirters in the mail today................Fancy Demon package.........STANDARD HOLLEY SQUIRTER.......:wtf:

Called Holley yesterday to see if they had a 750 main body that i could put on My 850 Demon. Gave him the part # of my carb.
He said point blank "That's a Barry Grant carb and i would have no idea if it would fit". That was the end of the subject. he had no other opinion about it.:realcrazy:

So round 2 i get a main body for my Holley carb....... NOPE!!! they only make them for 650 and up. My carb is a List 6776(600) and they only make them for 650 List 6777 and up.

Ordered a carb kit for the 600 DP
While try the, so called" Demon squirters" in it first, but i don't have much hope.
 
Cudafever said:
jetted it up yesterday. 82/90. thought it would be too much. but after adj the idle mixture screws, it ran the same.
snap the throttle in neutral and no sign of stumble. Put it in gear (3d) and wack the throttle no stumble. Stall a little and wack.......stumble.
Take it out on the road, stumbles from idle, stumbles at 2200 rpm launch.

Got my "Demon Squirters in the mail today................Fancy Demon package.........STANDARD HOLLEY SQUIRTER.......:wtf:

Called Holley yesterday to see if they had a 750 main body that i could put on My 850 Demon. Gave him the part # of my carb.
He said point blank "That's a Barry Grant carb and i would have no idea if it would fit". That was the end of the subject. he had no other opinion about it.:realcrazy:

So round 2 i get a main body for my Holley carb....... NOPE!!! they only make them for 650 and up. My carb is a List 6776(600) and they only make them for 650 List 6777 and up.

Ordered a carb kit for the 600 DP
While try the, so called" Demon squirters" in it first, but i don't have much hope.
Click to expand...



Time to sell that turd and buy the carb skrews has for sale here.

You'll be miles ahead.
 
Thank you so much for your help!!!!
I will be ordering it tonight when i get home!
 
skrews said:
This main body is a 1.375 venturi for 1.75 base plate, will flow 825 cfm with your base plate. I have one of these in one of my carbs, works nice.

Search Results for 67107C
Click to expand...

It will be here Wednesday.
It comes with main jets....Do you think i should start with them? Even though i Race at 6600 feet?
 
Looks like you’re on to trying a different body.
Good move.

Even on a big block the 1.56/1.75 downleg 4150’s can be a challenge to be good at the hit.
On a 400” motor with a modest converter, it’s really just the wrong carb...... especially at altitude.
The fundamental problem is the lag between the pump shot and the full activation of the main circuit.
The main circuit is activated by air flowing thru the Venturi and boosters.
Less cubes is less airflow...... and high elevation is less dense air...... a double whammy.

I would have expected to need way bigger squirters to use that carb on that motor.

My “good” carb is a ported old school Holley 850 annular, and even when I ran it on my 448 with 5300 stall it used like 40/40 squirters on it.
When I ran it on my 340 with a 4900 stall I used 45/47’s.

The old Holley 1.56/1.75 downleg 850’s came with a 50cc rear pump........ and on most combos....... they seem to need it.
 
Cudafever said:
It will be here Wednesday.
It comes with main jets....Do you think i should start with them? Even though i Race at 6600 feet?
Click to expand...

Yes, and drop down if needed. The carb I have with that mainbody was spot on with the supplied jets.
 
yellow rose said:
I'd be more worried about what air bleeds is has.
Click to expand...
The plus is that it has screw in bleed. Now i can learn how to do that. and if i mess up......i can just screw in the factory air bleed. i kinda read up on this a few years ago. But i didn't want to drill out a passage that may fix or destroy my carb.
 
PRH said:
Looks like you’re on to trying a different body.
Good move.

Even on a big block the 1.56/1.75 downleg 4150’s can be a challenge to be good at the hit.
On a 400” motor with a modest converter, it’s really just the wrong carb...... especially at altitude.
The fundamental problem is the lag between the pump shot and the full activation of the main circuit.
The main circuit is activated by air flowing thru the Venturi and boosters.
Less cubes is less airflow...... and high elevation is less dense air...... a double whammy.

I would have expected to need way bigger squirters to use that carb on that motor.

My “good” carb is a ported old school Holley 850 annular, and even when I ran it on my 448 with 5300 stall it used like 40/40 squirters on it.
When I ran it on my 340 with a 4900 stall I used 45/47’s.

The old Holley 1.56/1.75 downleg 850’s came with a 50cc rear pump........ and on most combos....... they seem to need it.
Click to expand...
Thanks for that! I had thought about a 50cc pump....but was undeside if it should be install on the from or rear pump.
 
skrews said:
Yes, and drop down if needed. The carb I have with that mainbody was spot on with the supplied jets.
Click to expand...
Thanks for all of your help!!!

So the problem really started late last year and has gotten worse this year.
It has drove me nuts because that was when i went from a 3000 stall converter to a 4200 stall.

What i finally....think i have figured out is the load between the two converter. The 3000 converter was a Stock Converter that was tweak to get 2800 out of my 340 and stall around 3000 with my 408.
The new 4200 converters stalls much higher for sure, But is TIGHT. in other words my 3000 converter took vary little throttle pedal to stall at 2200(rpm that i leave the line at) how ever to stall the new 4200 converter to 2200, it take more throttle/More Load to get to that same 2200 rpm launch speed. Now this year i started out with a 2 inch taller tire that added to the problem.
I may be wrong but that make sense in my mind. I just didn't get it when i first started fighting this problem.
 
Its more than likely a load and or acceleration rate of the motor giving the carb fits. The carb being so large has issues transitioning to (pulling in) the main circuit, creating the bog.
 
If you’re pushing the throttle farther down to achieve the same launch rpm(2200) with the new converter compared to the old one....... that uses up some of the pump shot/stroke...... so you get less remaining pump shot when you go to the floor.
 
Get a 50cc pump for the front and run #1 hole brown cam if you are running progressive secondary opening. Orange cam #1 hole on the secondary. I would start with 33 nozzles.
 
Main body i ordered says it comes with 33 nozzle, i have 37's next step. final step will be a 50cc pump and bigger nozzles.
hoping smaller main body will be enough.

My thoughts is to put the 50cc pump on the front. It seems all the factory 50cc pumps are always on the back/secondary side.
 
So YR's got me thinking about ordering me some bleeds.
when looking for a kit???? like i would for a fuel jet kit.!?
Why can you only buy individual bleed size, But you have to buy 10 of them??????? The carb only hold 4 each right? idle bleeds 4, High speed bleeds 4......Right?

Next question, does .001 make a noticable difference or are they like main jet and you should make changes in two step at a time AKA 76 to a 74

Next question if i have the throttle blades open far enough that the idle mixture screws makes no difference i need a larger air bleed....Right.

next question, outer bleeds are idle and inner are booster/high speed bleeds....right?
 
https://www.summitracing.com/parts/pro-67245
https://www.summitracing.com/parts/pro-67246

These are the kits I have. I usually go 2 sizes at a time to see any difference. The inner bleeds are the high speed bleeds and the outers are the idle bleeds. I'd start with 28 HS and 73 ID. I think that main body comes with 33/73 bleeds.
I you have the idle screw out so far that the idle mix screws make no difference you need to drill the throttle plates an back the idle speed screw down until the transfer slots look like squares. The smaller ID bleed will make the idle richer.
 
skrews said:
https://www.summitracing.com/parts/pro-67245
https://www.summitracing.com/parts/pro-67246

These are the kits I have. I usually go 2 sizes at a time to see any difference. The inner bleeds are the high speed bleeds and the outers are the idle bleeds. I'd start with 28 HS and 73 ID. I think that main body comes with 33/73 bleeds.
I you have the idle screw out so far that the idle mix screws make no difference you need to drill the throttle plates an back the idle speed screw down until the transfer slots look like squares. The smaller ID bleed will make the idle richer.
Click to expand...



Been so long since I've seen anything BG I can't remember if those metering blocks have adjustable emulsion, idle feed restriction and power valve channels?

You can always make them adjustable, I just don't remember what they came with.
 
yellow rose said:
Been so long since I've seen anything BG I can't remember if those metering blocks have adjustable emulsion, idle feed restriction and power valve channels?

You can always make them adjustable, I just don't remember what they came with.
Click to expand...

Fixed drillings IIRC, probably best left alone unless one really knows their ****.
 
Mighty and speed demon without the choke horn have screw in 8/32 MAB and IABs.
Here's some specs. The QF will help with your new Proform main body. Use the Q-series as a baseline.
 

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Mine for sure don't have pvrc,(Changeable chanel restriction) and i don't think it has a brass IIRC And i barely know what these letter stand for. Let alone how changing them would make it better or worse.
Fixed drillings IIRC, probably best left alone unless one really knows their ****.
So yes LTFA, AKA not touching them.
My demon carb is too old to have the Idle Eze on it, but it has 4 holes drilled in the butterflies already. (one per butterfly)

Been reading my holley book" Holley Carburetors & manifolds" by mike urich and bill fisher.
Just trying to refresh my mind on the butterflies hole drilling and the air/ high speed air bleeds.
I hope the holes drilled in the throttle shaft butterflies his big enough for the smaller main body. They were border line with the stock 850 Demon.
The mixture screws were adjustable, but the curb idle had to be raised above the square transfer slot setting i set before installing the carb. had to open up the primary and secondary idle screw to get it to idle.

Just for reference. I had a 5.5 power valve in the front and when i jetted the main jets up, i when to a 4.5 PV. It idles in neutral around 7 to 8 inch of mercury.
 
Cudafever said:
Mine for sure don't have pvrc,(Changeable chanel restriction) and i don't think it has a brass IIRC And i barely know what these letter stand for. Let alone how changing them would make it better or worse.
Fixed drillings IIRC, probably best left alone unless one really knows their ****.
So yes LTFA, AKA not touching them.
My demon carb is too old to have the Idle Eze on it, but it has 4 holes drilled in the butterflies already. (one per butterfly)

Been reading my holley book" Holley Carburetors & manifolds" by mike urich and bill fisher.
Just trying to refresh my mind on the butterflies hole drilling and the air/ high speed air bleeds.
I hope the holes drilled in the throttle shaft butterflies his big enough for the smaller main body. They were border line with the stock 850 Demon.
The mixture screws were adjustable, but the curb idle had to be raised above the square transfer slot setting i set before installing the carb. had to open up the primary and secondary idle screw to get it to idle.

Just for reference. I had a 5.5 power valve in the front and when i jetted the main jets up, i when to a 4.5 PV. It idles in neutral around 7 to 8 inch of mercury.
Click to expand...



You set power valve opening by cruise vacuum and not idle vacuum. The book is wrong on that.
 
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