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Old 01-25-2011, 03:54 PM
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Problems with my 750 Speed demon carb. Help!!

Ok so i have a fresh 383. I recently upgraded my intake to a edelbrock air gap intake and a speed demon 750cfm mechanical secondary electric choke annular boosters. It runs and i drive it as my everyday car for the summer BUT

First problem= when i start it it idles normal when warming up but if i try to give it any gas it pops and sputters. if i take my foot off the gas it dies so i have to keep it floored to keep it alive until it warms up. This also happens even if the car is warmed up but just shut off for a while (20+ min) . It seems like it is flooded and has to clear out or something?

Second problem= The float levels keep changing? I have to adjust them a few times a week usually. is this normal for speed demon carbs?

Third problem= It wont idle down lower than 1000 rpm (before this carb it idled around 6-700). I would like to lower the rpm if possible but it if i try to go lower than that it kills the engine.

When the engine is warm it runs fine at open throttle and just norm driving besides the whole idle thing
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Old 01-25-2011, 04:08 PM
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First thing that comes to mind to me is you have a major vacuum leak somewhere. That is one of the signs of a vacuum leak is being unable to get your idle down. Second thing that comes to mind is check your choke and make sure it's opening all the way and also if you have an inline fuse check it to make sure it has not blown. Also check to make sure your timing and everything else is checking out ok as well such as ignition,charging etc.

Also check to make sure your secondary's are not open too far as well. Try to make your primaries opened up about the same as the secondaries so you have equal amount of air flow. You did not state the size of your cam and if its a big cam that is a whole other story. On your fuel level no it is not normal for any carburetor to have its level needing to be changed several times a week. Excess fuel pressure can cause fuel level issues like that. Hope you can find out what is going on.
Eric
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Old 01-25-2011, 04:25 PM
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Im not 100% positive because the build was a few years ago but i am pretty sure the cam duration is 230. and its a '79 camaro, would their be a fuse for that? And yeah i have looked around on the web and fuel pressure may be a reason for this but im not sure because i have a mechanical fuel pump and it worked fine before when i had a 600 edelbrock on it
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Old 01-25-2011, 06:18 PM
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Different carbs have different fuel pressure requirements, and do's and don'ts. Look on BG's site for their recommendations.
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Old 01-26-2011, 11:08 AM
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I am a huge fan of BG carbs. With the float level changes, I would agree with 68Nova on fuel pressure. What do you have it set at?

You could try the BG tech line. Depending who you talk to, getting a straight answer can be a challenge. At least that has been my experience.
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Old 01-26-2011, 11:15 AM
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Dear 1000rpm idle,

It has come to my knowledge your demon carb will not idle below 1000. First first. Does the engine die when all idle adjustment screws are sunk in? If so you are pulling fuel from above the idle ports. If it dies, then it is mainly fed from the idle ports the answer lies there. Idle EZ is availible, and are interchangeable idle air bleeds the most important. Depending on cam you may need to increase the port size, or decrease to fit the engines vacuum needs.

Sinning constantly,
Racer X
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Old 01-26-2011, 02:23 PM
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Clarifing 3 rd sentence , that Engine continuing to run will indicate it is pulling from above the idle ports. If it dies, with screws in adjust the idle bleed or port size.

Second , no Floats stay. Look for fuel leaks around the adjustment nut. That can tip you to a loose lock nut. Float tang damage, and a sticking needle should be looked into.

The idle system has no effect on cruising.

Problems 1 and 3 are probably related . If the engine has a incorrect idle mixture or choke setting, cold starts can be tricky. Same with frozen solendiods on QJets.
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Old 01-26-2011, 03:52 PM
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Ok well reply to the fuel pressure is that im not sure. i have the stock mechanical fuel pump on the engine and no fuel pressure gauge so im not sure.

and with the screws i have not been able to screw the 4 screws in all the way without it killing the engine.

I cant really play with it much until it is warmer out due to the fact that i live in WI and do not have a heated garage.
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Old 02-01-2011, 10:11 AM
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How much timing does the motor have in it at idle? How much vacuum at idle? What rpm does the engine go to when it is on the fast idle for the choke?
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Old 02-01-2011, 12:02 PM
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well i wont be able to tell you exact with the idle and vacuum until it warms up and i can get it going again. but to be honest the choke dosent really change the idle much. like it stays the same and when the car warms up the idle actually rises im pretty sure. I know its opening because i have watched it do this.
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Old 05-01-2013, 04:32 PM
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hello have you ever drilled the idle circuits out on a demon? talked to b/g today and my carb don't have the air bleed jets so they said to drill the circuit in the block?
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Old 05-01-2013, 04:47 PM
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Quote:
Originally Posted by brewstersta View Post
hello have you ever drilled the idle circuits out on a demon? talked to b/g today and my carb don't have the air bleed jets so they said to drill the circuit in the block?
b/g is out of business, you have to contact holley
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