Street Demon Experience for you guys

[demian5]

Ok, so I got a brand new phenolic body street demon carb (thermo quad). I had an Edelbrock Q-Jet on there before. I rebuilt the Q-Jet but it never ran right. Only one side would respond to mixture adjustments and I could never adjust the idle down past 850 when warm. I wasn't really happy with the dash pot choke either. I'm running 14 BTDC on basically a stock motor with mid-length headers, MSD billet distributor and a performer intake.

I hope my info helps someone with their install or decision.

Putting the new carb on and getting dialed:

• Sucks having to cut up a good hard line, but used small pieces of hose, and put a metal filter in between. Used the 90 degree turn from the old line to make the turn in the line at the rear of the carb.
• The PCV needs to be relocated to the passenger rear of the valve cover as that is where the nipple is on the Demon Carb. So say Bye-Bye to the factory air cleaner spacer and crankcase vent.
• The PCV nipple points at the vacuum fitting for the trans (if you have that screwed into the intake still) and the hose hits it when connected. Remove the fitting, plug the hole and hook trans hose to the manifold vacuum nipple right next to the PCV nipple instead.
• Good luck with the throttle hookup, you are on your own. Luckily I had a bracket from another vehicle that worked but had to massage it to work.
• For the return spring, this is tough as the normal throw of the spring and bracket I have crossed over the kickdown cable, had to massage bracket again.
• The drop base air cleaner hits the accelerator pump linkage, causing the idle to race through the roof (thanks to having to get rid of my factory air cleaner spacer). Needed to use an old 75 Chevy Air cleaner assembly I had in the shed. It's OK, just temporary.
• It idled high still! At 1000! Well, after research, even with electric choke hooked up and warm, the fast idle adjustment screw was in all the way, causing the butterflies to stay open no matter how I adjusted the idle screw. Loosened it up, I can idle at a smooth 500 in P if I want, but went with 700 and a smooth 500 in D.
• Had a flutter in the carb when the secondaries hit under medium throttle, adjusted the spring for the air horn butterfly of the secondaries. Seemed better but a definite flutter still, not as bad.
• Found the flutter,, the air horn butterfly was hanging up on the rear of the carb where it goes around an air vent. Pulled the butterfly off and used a rat tail file to clearance. Flutter now gone.
• Still messing the kickdown cable adjustment. Instructions say to put on hole farthest to the front of the vehicle. If I do this I can't get full throttle. I have it in the middle and the cable is maxed at full throttle but the trans doesn't seem to shift as well as it did with the Q-Jet.

I gotta tell you, the seat-o-pants dyno is stoked. It hauls ass now and can smoke the tires (it wouldn't before), and chirp them in 2nd. I am a Q-Jet guy and usually have great luck with them (I build and tune carbs all the time), but this Edelbrock made one just never came around.

[RedRider]

Great info! I recently did a similar swap but went with a speed demon instead. Lots of similar issues though; throttle linkage, PVC valve etc and I wish somebody like you would’ve posted all these great tips for my reference.

[EVRLET]

I have a Demon 625 and it ran super rich out the box. I have the idle mixture screws about 3/4 turn open from completely closed. Have an AFR meter with dual O2s and it reads between 13.6 and 14.2 at idle, cruise and WOT. To me it seems crazy that the set screws are barely open, but the AFR is where it should be.