Well Ive had a 750 Mighty demon on my 383 for a while now, The first year i put it on, the thing was real quick. Last summer, the thing sucked, ran rich, fouled plugs all the time. Well I brought it to the body shop, which is a pretty good one, been around for a while, and I trust them, saying I should throw a 650 edelbrock AVS on there. They are saying its wayyy to big (demon). I called barry grant, and they said that if everything is the same, and it was running rich, that I should rebuild the carb. So I did, and ran the same. I tryied tuning it, the fuel level is set at the bottom of the sight plug, like they told me for street cars, and and I messed around with the jets, but If i go in either direction, it gets a bog. sooo yeah...

The Edelbrock would be a downgrade from the Demon. How thorough of a rebuild did you do?

I bought the kit from BG. I replaced all gaskets, acel. pump disphams, needle and seat, idle mixture screws and o-rings, I cleaned every orifice with carb cleaner then blew it out with shop air. I cleaned the throttle plates, put a new PV in it. While it was off i adjusted the Idle transfer slots to look like a square, like BG wants.

You didn't make any changes before it started having problems? You're sure your ignition system is in good shape?

yup. when it was loading up, I changed plugs, put on MSD wires, MSD cap/rotor. I have a MSD pro-billet HEI distributer in it. The only thing that changed was I did a TH 350 swap, so, nothing to do with the engine running rich.

I have owned several demons, currently own a 750 Speed demon. They all ran very rich at idle, and you have to turn the 4 corner screws in to under one turn out to lean them out. I have successfull tuned them useing a vacuum guage, adjusting to max vac. But what really works is a wide band air fuel sniffer. I can't this moment remember the brand name. runs about 300$ if I remember correctly. I was able to tune the four courner idle mixers to a reasonable 13/1. These idle mix screws also control the low speed off idle running. The screws come with a small rubber O ring, which some time rot away, and the threads can also become worn, so I use a little lock tight to seal and hold the screws in place.
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I have a question about carb application. I am going to put a 700R4 in my next project car, which is a 30 something 5 window coupe gasser. I use a demon with mechanical secondarys on my 60's muscle car manual trans. I am looking to buy a used demon on ebay, but I don't know if I have to use vacuum secondary carb or can an auto trans car use a mechanical secondary?

What body shop? Gotta say it shouldn't be too big. I have a 750 speed demon on a 355 that runs great!

sure can

Master auto body

call up a local speed shop and they'll point you in the right direction to get it dyno tuned with wideband, that should set everything up properly.

As bad as I dislike a Q-JET I'd rather have one to an EDELKROK any day!!!!

Yeah I guess ill have to do that. Ill let you guys know what the out come is.

edelbrock carbs are fine for very mild street cars with a square boar intake but i wouldn't but in in anything with a decent amount of horse power.

and your body shop steered you wrong if the carb was too big it would run lean not rich. I have your exact same problem with my 355 with a 750 ts speed demmon. Defintly take it to a dyno or get this. If you cant get it to lean out with the wideband then drill and tap your air bleeds to 10 32 so you can put in scrue in air bleeds and try putting in a biger size low speed air bleeds. i am doing that this very spring.