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Old 03-17-2005, 09:59 AM
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Barry Grant Demon carb

Hope someone can help me out.

I have a Demon 850 cfm w/vac secondaries and an electric choke on a caddy 500ci
I have the the thing all tuned correctly and runs great. The problem is getting the engine started when cold. Ill turn the key and hit the gas to set the electric choke. when it first starts up it runs very very lumpy and spews rich black smoke out the pipes. I need to keep my foot lightly on the gas so it doesnt die on me.Once the butterfly starts to open just a bit it leans out and runs great but then ill still have to continue to hold the gas because the "fast idle" is not working. I messed with the fast idle screw a bit but not fully understanding how it works and exactly what it affects I dont want to mess with it to much. I have also tured the black choke horn both clockwise and counter clockwise but still have a lumpy smoky start up and need to sit there till up to temp..
When it comes to Demon carbs im not very knowlegeable. I have bought the book and read it a few times but have not found the answers im looking for (or im overlooking them). I dont find the book to be very specific in what I am looking for.The only time i have to call BG tech is the weekends and there is never an answer.

I would appreciate any tips or suggestionss you guys may have

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Old 03-17-2005, 01:44 PM
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It sounds like your choke idle feed screw needs to be opened up a bit. This screw sets the primary throttle blade position when the choke is set. It is below and in front of the throttle linkage.
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Old 03-17-2005, 04:06 PM
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so, i should set the primary butterfly's .020+ open using the idle screw, then tune the carb using the 4 adjustement screws on each side of the bowls. After that is done I will need to readjust my choke plate and fast idle screw.
Is this correct ?
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Old 03-17-2005, 04:52 PM
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Yes, you need to do all those things but to solve your startup issue you need to set the choke idle screw so it opens the primaries a bit more so the engine gets air. This screw should pull off the primaries once the choke is off so it won't affect the tune on the carb once it's warmed up. You want to verify that after the choke is open it is not holding the primaries open. If the engine idles fine when warm i don't think I'd mess with the base iidle screw setting just yet, unless it is way off from the .020 figure.

Once warmed to operating temps then you can set the 4 corner idle.
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Old 03-24-2005, 12:12 PM
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Tuning a Demon

Gilby,

All of the tuning needs to be done once the engine is warmed up to operating temp. As far as your starting problem goes it sounds like you do not have enough fast idle RPM. Normally you need to have the fast idle (when the choke is engaged) 600 to 800 RPM higher than your idle once everything is warmed up. So if the engine idles at 800 RPM when it's at temp, it should be between 1400 & 1600 RPM when the choke is engaged. To do this you'll turn the fast idle speed screw (behind the choke pod) clock wise. You can usually reach this with a small open end wrench. This should take care of your starting problems.
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