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Thread: what's up with the demon?

  1. #1
    Senior Member
    Join Date
    Feb 2009
    bought a demon upon much recomondation , hooked it up and it wont idle
    might demon 850 mech. sec. just hope it wasnt a bad choice.

  2. #2
    What is it on top of?? 850 is alot of flow.........MP

  3. #3
    Senior Member
    Join Date
    Feb 2009
    a 454 which is also for the most part a big mystery

  4. #4
    scott williams
    I belive the idle is a "four corner" idle setup, very tricky.
    both the primary and secondary throttle plates have and idle adjustment, and four idle screws, if you are using even a moderatly radical cam profile, it may be difficult to get a solid idle below 900-1100 rpm, NOT impossible, just tedeous and time consuming. I helped a guy with a 454 tune a demon, tricky! tiny adjustments, never got it to idle below about 975 rpm, cam was hydraulic, some custom grind in the 300-310 "advertised range.
    good luck, the carbs seem to be well made, and certainly no more difficult than an equivilent holly with 4 corner idle.

  5. #5
    According to the literature that came with my 850 Mighty Demons, you set the throttle plates to properly expose the transfer slots and adjust the idle with the screw in the hole where the air cleaner screw goes. Haven't tried it yet, still putting the finishing touches on the motor.

  6. #6
    scott williams
    Yeah, isn't the center screw an "additional air bypass" the demon version of drilling holes in throttle plates. this is used to increase air flow at idle so you can keep the transition circuit "out of play" at idle speeds?

  7. #7
    Senior Member
    Join Date
    Feb 2009
    I set it up just as the booklet suggested , transfer slots , floats , 1-1/2 turns out on the idle screws and I have about 7 psi of fuel goin to it and it still did no idle . I called there bg tech line and the fellow says that the idle feed restrictors might have been drilled out and if thats not it then its something in the main body and it'll have to be sent back to be gone through again. Now without letting too much on I had already completely taken it apart and the idle feed restrictors were drilled and I had been in every hole and crevis like a one night stand and ironically I did find metal shavings in some of the main body passageways. Was that my problem ? I dont know but it wont help .The hole in the restrictor should be the same as a #62 drill bit so tomarrow I will see what the fuzz. Everyone always has great advice and being new to this as well as the boards is like being a kid in a candy store.

  8. #8
    Pee Dub
    Guess I got lucky with the 2 Demons I purchased. Both ran perfect out of the box and were way more responsive than any Holley I have ever owned. I followed the BG recommendations as to matching the series of carb to the @.050 duration of the cams.

  9. #9
    Senior Member
    Join Date
    Mar 2010
    RumRunner on OSO and Speedwake is Doug S, he is head of technical support for BG and a sharp guy. You may want to do a search on either board and PM or e-mail him. Super guy to work with.

  10. #10
    My 850 demon would never work properly, even with all the work and assistance I could muster up. I bought a new holley and all the problems went away with the new carb.

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