Barry Grant Demon carb - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gilby246 · 03-17-2005, 02:38 PM

Hope someone can help me out. Have been reading this board for a while but this is my first question I have posted

anyway

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

northern 85 · 03-17-2005, 08:28 PM

Sounds exactly like what im going through,i have a crate demon 650 on a goodwrench 330hp vortech.The tech @BGI told me that the fast idle rod can get knocked out of position if bumped during shipping.I checked mine and it seemed like it was riding in the black linkage wich is connected to the choke.So i decided to check the fast idle setting.With the engine cold and the choke activated the fast idle screw head is facing the firewall,its tough to get to but can be done with a small screwdriver,i turned the screw in one half turn and tried it.The fast idle did work but still had to rotate the choke adjustment clockwise to open the choke.Called them back and said its still rich on choke, he asked what my timimg was set at because demons like 12 degrees to create more vacume. I missed that in the manual! Thats where i am now so ill let you know how i make out,going to play with the 4 idle mixture screws tomorrow to see if i can create more vacume. What are you running for a air cleaner?

Grim Reaper · 03-17-2005, 09:14 PM

Man you guys are scaring me.

I just picked up a Built 400 poncho with a Edlebrock high rise and a Demon 750 for my 70 LeMans. We fired it off before it was pulled so I could hear it and then did a compression check. (damn near 162 on all 8). I noticed it was rich big time when it started. When I did the compression check I looked the plugs over it also showed very rich. Not in the car yet so not had a chance to play with it. I will be watching this thread to se the outcome.

Making me wonder If I should have bought the factory Quad when it was offered. I did get the factory 4bbl intake so If I FI it with the 454 FI I have I can bolt it on.

gilby246 · 03-17-2005, 11:56 PM

yeah it appears my fast idle cam had moved as well. either from all the tuning i did to the damn thing trying to get the motor to just run or in shipment.

anyway, first I messed with the fast idles screw a bit. I think there are two "steps" in the fast idle cam this screw can be set on..what one im to useing is beyond me. I used one of them and set my choke so it was just open a bit. i used the idle screw and turned it in a bit to open the main butterfly's more and then after the engine was running i used the 4 idle mixture screws to tune it down some more. From my understanding the main butterflies need to be opened .020 i dont beleive mine were open enough so i was getting rich at start up.
After I did this I had to adjust the accelerator pump lash (seeing as I adjusted the idle screw) so it didnt to that bog down thing when you hit the gas kinda hard.

It seems to start now ok (still not great) without that thick rich smoke but I still have no fast idle and I cant figure it out

northern 85 · 03-19-2005, 02:26 PM

When your choke is activated(closed) it pulls the choke rod up which pulls on one side of the black fast idle cam lowering the other side with the steps. The steps are what your fast idle screw is supposed to sit on when acctivated. If you adjusted your choke from closing all the way on a cold start it isnt letting the black stepped cam drop far enough to come in contact with the fast idle screw.I tested mine by turning the choke control counter clockwise so the choke would fully close then rotate the throttle linkage twice like you are pumping it to start it.This will set the fast idle.Now set the choke control back where you had it befor by only touching the choke control nothing else,this should open your choke back up.Try to start it dont touch the gas pedal or it will deactivate your fast idle let me know how you make out.

gilby246 · 03-21-2005, 02:50 PM

thanks, so far thats the best decription i have gotten yet.

Didnt have time this weekend to play with it. If its not cold and raining tonight ill do as you suggested and post the outcome

northern 85 · 03-22-2005, 10:48 PM

Primary and secondary butterflyes are supposed to be open equal amounts the set screw for the secondary is a very small allen set screw down by your fast idle screw clock wise to open, if you have a set of medium length allen wrenches it easy to adjust with out removing the choke.

gilby246 · 03-24-2005, 09:55 PM

Thanks Norther 85

did as you said and got it working. That fast idle cam was WAY off. Must have turned that screw a good 3 full turns.

Thanks for the help

dion · 03-24-2005, 11:51 PM

I have a speed demon also, there a BG tech on this site, he's super cool and will help you with any problems.

http://hotrodders.com/forums/forumdisplay.php?f=21

Tech @ BG · 04-08-2005, 08:38 AM

Northern 85 has said it best... To use the electric choke on a Demon you must first depress the throttle once or twice. This will give the engine a shot of fuel from the accelerator pump, and set the fast idle speed screw on the cam. The fast idle should be set at least 600 RPM higher than your normal at temp. idle speed. Once you've depressed the throttle, and start the engine, do not touch the pedal again. Once the choke starts to open, if you depress the throttle the engine will come down off of the fast idle. On my 86 when I had a carburetor with a choke on it I would press throttle once, turn the ignition on (this would put power to the choke coil), wait about 10 seconds, crank the key, and she'd light right up. After that about 45 seconds later she was good to go. Although winters here don't get much lower than the teens at night. Sounds like you're going in the right direction.

03-17-2005, 02:38 PM	#1
gilby246 Registered User Join Date: Mar 2005 Location: seattle Posts: 24	Barry Grant Demon carb Hope someone can help me out. Have been reading this board for a while but this is my first question I have posted anyway 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

03-17-2005, 09:14 PM	#3
Grim Reaper Registered User Join Date: Jul 2001 Location: Atlanta GA Posts: 1,704	Man you guys are scaring me. I just picked up a Built 400 poncho with a Edlebrock high rise and a Demon 750 for my 70 LeMans. We fired it off before it was pulled so I could hear it and then did a compression check. (damn near 162 on all 8). I noticed it was rich big time when it started. When I did the compression check I looked the plugs over it also showed very rich. Not in the car yet so not had a chance to play with it. I will be watching this thread to se the outcome. Making me wonder If I should have bought the factory Quad when it was offered. I did get the factory 4bbl intake so If I FI it with the 454 FI I have I can bolt it on. __________________ Grim-Reaper 70 Pontiac LeMans Sport Convertible, worlds longest resto in progress Looking for 71-72 2wd Blazer or Jimmy Project

03-24-2005, 11:51 PM	#9
dion 72 Cheyenne Join Date: Oct 2001 Location: San Diego Posts: 2,086	I have a speed demon also, there a BG tech on this site, he's super cool and will help you with any problems. http://hotrodders.com/forums/forumdisplay.php?f=21 __________________ Burnout Idle 1972Cheyenne 1966/67Stouts

03-17-2005, 08:28 PM	#2
northern 85 Registered User Join Date: Mar 2005 Location: Fairfield Maine Posts: 1,759	Sounds exactly like what im going through,i have a crate demon 650 on a goodwrench 330hp vortech.The tech @BGI told me that the fast idle rod can get knocked out of position if bumped during shipping.I checked mine and it seemed like it was riding in the black linkage wich is connected to the choke.So i decided to check the fast idle setting.With the engine cold and the choke activated the fast idle screw head is facing the firewall,its tough to get to but can be done with a small screwdriver,i turned the screw in one half turn and tried it.The fast idle did work but still had to rotate the choke adjustment clockwise to open the choke.Called them back and said its still rich on choke, he asked what my timimg was set at because demons like 12 degrees to create more vacume. I missed that in the manual! Thats where i am now so ill let you know how i make out,going to play with the 4 idle mixture screws tomorrow to see if i can create more vacume. What are you running for a air cleaner?

03-17-2005, 11:56 PM	#4
gilby246 Registered User Join Date: Mar 2005 Location: seattle Posts: 24	yeah it appears my fast idle cam had moved as well. either from all the tuning i did to the damn thing trying to get the motor to just run or in shipment. anyway, first I messed with the fast idles screw a bit. I think there are two "steps" in the fast idle cam this screw can be set on..what one im to useing is beyond me. I used one of them and set my choke so it was just open a bit. i used the idle screw and turned it in a bit to open the main butterfly's more and then after the engine was running i used the 4 idle mixture screws to tune it down some more. From my understanding the main butterflies need to be opened .020 i dont beleive mine were open enough so i was getting rich at start up. After I did this I had to adjust the accelerator pump lash (seeing as I adjusted the idle screw) so it didnt to that bog down thing when you hit the gas kinda hard. It seems to start now ok (still not great) without that thick rich smoke but I still have no fast idle and I cant figure it out

03-19-2005, 02:26 PM	#5
northern 85 Registered User Join Date: Mar 2005 Location: Fairfield Maine Posts: 1,759	When your choke is activated(closed) it pulls the choke rod up which pulls on one side of the black fast idle cam lowering the other side with the steps. The steps are what your fast idle screw is supposed to sit on when acctivated. If you adjusted your choke from closing all the way on a cold start it isnt letting the black stepped cam drop far enough to come in contact with the fast idle screw.I tested mine by turning the choke control counter clockwise so the choke would fully close then rotate the throttle linkage twice like you are pumping it to start it.This will set the fast idle.Now set the choke control back where you had it befor by only touching the choke control nothing else,this should open your choke back up.Try to start it dont touch the gas pedal or it will deactivate your fast idle let me know how you make out.

03-21-2005, 02:50 PM	#6
gilby246 Registered User Join Date: Mar 2005 Location: seattle Posts: 24	thanks, so far thats the best decription i have gotten yet. Didnt have time this weekend to play with it. If its not cold and raining tonight ill do as you suggested and post the outcome

03-22-2005, 10:48 PM	#7
northern 85 Registered User Join Date: Mar 2005 Location: Fairfield Maine Posts: 1,759	Primary and secondary butterflyes are supposed to be open equal amounts the set screw for the secondary is a very small allen set screw down by your fast idle screw clock wise to open, if you have a set of medium length allen wrenches it easy to adjust with out removing the choke.

03-24-2005, 09:55 PM	#8
gilby246 Registered User Join Date: Mar 2005 Location: seattle Posts: 24	Thanks Norther 85 did as you said and got it working. That fast idle cam was WAY off. Must have turned that screw a good 3 full turns. Thanks for the help

04-08-2005, 08:38 AM	#10
Tech @ BG Registered User Join Date: Apr 2005 Location: Dahlonega,Ga Posts: 45	Northern 85 has said it best... To use the electric choke on a Demon you must first depress the throttle once or twice. This will give the engine a shot of fuel from the accelerator pump, and set the fast idle speed screw on the cam. The fast idle should be set at least 600 RPM higher than your normal at temp. idle speed. Once you've depressed the throttle, and start the engine, do not touch the pedal again. Once the choke starts to open, if you depress the throttle the engine will come down off of the fast idle. On my 86 when I had a carburetor with a choke on it I would press throttle once, turn the ignition on (this would put power to the choke coil), wait about 10 seconds, crank the key, and she'd light right up. After that about 45 seconds later she was good to go. Although winters here don't get much lower than the teens at night. Sounds like you're going in the right direction.



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