My 67 camaro has a 396 SB with a Demon 825 carb. I have no complaints on driveabilty. Throttle responce is awsome. But, the problem is that I am fouling plugs at idle and and reving. My knowledge on carbs is pretty good but the only thing I dont really understand are the idle air bleeds and air bleeds. I had .080 jets in the primary, now I have .074. That helped a bit but not enough and I dont know if I want to downsize anymore.

Please give me some headway!

Thanks!
Sean(Pig)

 

Demons are not like holleys in the respect they run on the idle circuit alot longer than a holley. The idle mixture screws are extremely important on a demon. If you watch the boosters on a holley they will start pulling fuel in at 1200 to 1500rpm where a demon won't until around 2500 to 3000 rpm.
Changing the main jets won't fix you're problem (A common one). you need to screw the idle mixture screws in. Keep in mind they a 1/16 of a turn (on all 4) is alot on a demon so go slow.
I don't know how much you know about carbs so I'll tell you to do it this way.

1 Screw all mixture screws in all the way.
2 screw out 1 and 1/4 turns on all screws.
3 start engine if it won't stay running screw out another 1/4 round
4 restart and screw out in 1/8 turns incerments on all 4 till you get the highest idle. If the idle gets to high close the throttle plates and repeat turning screws.
5 once you get the highest idle slowly turn back in 1/16 turns till it just starts to drop idle or slow down.
6 test drive if it has a off idle(tip in) stubble or hesitation screw out mixture screws 1/16 each til it goes away.
7 If you have to screw out the screws to remove hesitation you may have to call jerry dooley at Berry grant and tell him you need another base plate with a diiferent transition slot.

If the throttle plates are to far open it will uncover the trans slots and will not work properly. both Primary and Secondary are suppost to be open evenly. If you're out more then three turns on the idle mixture screws you need restictors in the idle air bleeds.
Idle air bleeds do just what they say the do they bleed air into the engine at an idle so if the screws are out a long ways this means you are having to add alot of fuel to the idle mixture and need to restrict the air bled into the curcuit.
high speed air bleeds do the same thing at higher rpm or at a high velosity of air going throught the venturas. let's say the engine makes best mid range power with a 75 jet but if you use a 73 jet it looses midrange but picks up power at the top. You would go back to the 75 jet and put a smaller high speed bleed jet to lean it out on the top end and have the added midrange of the 75 jet but the top end of the 73 jet. Basically they control the fuel curve in the carb.
The inner bleeds are the idle and the outer are the high speed. If you take you finger when it's idleing and partially block the idle bleeds and the motor speed up the idle curcuit is lean, if it try's to die it fat.
HOPE THAT HELPS

 

Thanks again Taylormade!

I will give you advice a shot tomorrow and let you know how it goes.

You explained very well!

Sean(Pig)

 

Taylormade, I found that my highest idle was with the idle mix screws 1/2 turn out. The engine cleared up big time. The idle adjustment screws were not in tune, now there are and it made a nice difference in the idle quality.

My question is why only 1/2 turn out on the idle mix screws? Plus when you say cover up the idle air bleeds with your finger do you mean cover up all the idle air bleeds or just one or two?

Where do I go from here?

Thanks!
Sean(Pig)

 

I meant 2 of the air bleed either primary's or secondarys. I meant you to use that as a self check when done. 1/2 a turn out is OK but they are usually out farther than that alot depends of camshaft size and the displacement of the motor. If you're in that far you should check the power valve to see if it's blow.
Install a vacumn guage at an idle and see what it is. lets says its got a big cam in it and it has only 5 inches. Your carb should have 6.5 inch power valve that means it's opening at an idle and richening the mixture. You would need to go to a 2.5 or 3.5 power valve.
The power valve enriches the mixture at high throttle settings (low manifold vacumn) this allows the carb to not be so rich under normal driving conditions.
Without doing dyno testing you should not mess with high speed air bleeds. The rest is normal jetting of the primary and the secondary

 

Thanks alot Taylormade! Oh meant to ask you the inner air bleeds are the high speed and the outter air bleeds is for idle, right? I covered up the inner air bleeds and the engine didtnt do nothing I covered up the outter air bleeds (all four) and the engine wanted to die. Dont know if that was mix up.

The carb does have a 6.5 power valve in it and I will check the vaccum at idle on Monday.

You have been a big help.

The car will be going to a dyno with a wide band in about a month. Is there a tuning kit I can buy for this carb with air bleed jets and main jets? And, is there any tips I should know when the car hits the rollers?

Thanks again,
Sean(Pig)

 

Outer are the idle and inners are the high speed. Most people wont mess with the high speed ones. I'd recommend the same, unless you see better power low to mid range with one jet and better high end with another jet but the low and mid range suffers or less power on both.
If you have access to drill bits in thousandths you can drill the air bleeds out or can silver solder them and redrill them smaller till you know what size you need then just buy the ones you need. I do this alot as it always seems like you don't have the size you need on the shelf.

 

Thanks for the help and advice.

Sean(Pig)