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Carb difference

1K views 5 replies 4 participants last post by  PA_cob 
#1 ·
So I was running a Street Demon 625 carburetor on my car for the past 2 years. Ever since I installed it I had experienced all kinds of issues with the car. Over heating, flooding, idle issues. I have suspecting that there was something wrong with the carburetor. A lot of things got better with my move from Colorado to Texas. But the one thing that still bothered me was the idle inconsistency. Some times it would idle around 700 sometimes 900 sometimes 600. In Colorado I could only ever manage 15 inches of vacuum. Here in the Texas I was getting 17. I finally changed over to a Holley 4160 600 cfm carb the other day. Idle has improved, and crazy thing is that am now getting 20 inches of vacuum. I think there is a throttle plate issue with the Street Demon as it the secondaries seem to be hanging up. Also do to such a big jump in vacuum I am wondering if maybe there wasn't a leak somewhere. I really liked how the Street Demon worked under throttle. I am going to pull it apart and replace all gaskets and see if I can get the throttle plates aligned.
 
#2 ·
I have no experience with the Holley street demon but it looks very similar to the CarterAFB/Edelbrock.
So the same tuning methods should apply to the street demon. Especially float level setting.

I’m a fan of the CarterAFB and would like to see more of the functions and parts inside the street demon.
 
#3 ·
I would agree with you about a air leak somewhere. Besides leaning out the mixture it’s going to reduce the signal across the Venturi and possibly give erratic readings which is going to effect the fuel circuit and mixture.

I’m not trying to start up that Edelbrock vs Holley debate but I prefer carbs that use annular boosters. They’re more sensitive and give better response and fuel atomization no matter the carb brand. This is what made the Autolite 4100 so popular and why folks like the Summit and Edelbrock or any other with these boosters.
 
#4 ·
Demon Carb

For whatever it's worth, I had a new Street Demon on my mildly built 289 and it ran like crap. Took it to the dyno, had it tuned, etc. and it never ran great. I swapped to an Edelbrock 650 and the motor came to life. Smooth idle, great throttle response, etc. I chocked it up to the Demon having too many fine adjustments that a backyard mechanic could never sort out but I am now not a fan at all for the Demons.
 
#5 ·
It was mainly just the idle that really had me frustrated. I am going to pull it apart, clean it, see if I can realign the throttle blades to not hang up, and out it back together. @Huskinhano @MrFlash I believe that the Street Demon uses annular boosters as well. I addition the primary side is small vs other carburetors. I generally found the low end response to be excellent. I also feel like the secondaries open faster and smoother in the street demon vs the Holley. I will take some pictures of it disassembled and post them for comparison to a Carter/AFB. Once it's back together I will give it one more shot on the car.
 
#6 ·
Wow so there is a huge difference in how this Holley runs vs my Street Demon. I have been messing around with the carb and timing. I have vacuuum advanced dialed in. Now when I am rolling in 1st gear I can punch it and the car will flat out do a burnout. This happens from a roll sometimes in second as well, more of a tire squeel then burnout though. In first it will straight roast the tires and get a little sideways. With the Street Demon I could never do that. Had to dump the clutch to get a burn out. I still think there was something wrong from the start with the Street Demon.
 
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