Those with Street Demon Carburetors....

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RustyRatRod

RustyRatRod

I was born on a Monday. Not last Monday.
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I just put a used 625 Street Demon on my 75 F250. 351M, Weiand Action plus, GM style HEI 20* initial and 35 total in by 3000. Exhaust manifolds. I THINK it MIGHT have the Melling, TRW, Elgin, "everybodys" grind that's like 204/214 @ .050, but on a Ford the lift is more because of the 1.73 rocker ratio. .484 and .512.

Anyway, I got the carb in a trade. It needed some repairs. The secondary air door spring was broken. Thermoquad air door spring fits perfectly. Put a kit in it. Cleaned it all up lookin like new.

This thing runs like a bat out of hell now. When that secondary door opens, this big old truck moves. Anyway, I am noticing something a little different from other carburetors and wondered if others running these noticed it too.

There's "not a lot" of the primaries. In other words, the primaries have a kinda short travel. The secondaries come in pretty quick with the pedal travel. I kinda like it. Anybody else notice it?
 
I have and I LIKE it. Motor goes from mild to wild when the secondaries open. Sounds awesome. I love my street demon carb. I'm planning on getting the larger one to replace my 625 and hopefully free up some power.
 
Sounds about like the old smallblock TQ on a 318 with a midrange cam. The primary's are pretty tame, and the secondary's....aren't.
 
I'll have to get Kitty to work the video camera so yall can see how effective this thing is. It's a 75 F250, do it's NOT light, but it slap gets up now.
 
Kindof like the TB in my 92 Explorer was. The first 30% of the pedal travel opened her up probably over 50%, and bam! she jumped off the line. But there wasn't much left from there to full pedal travel.
My wife's Honda Pilot is like that too, and in addition it has a fairly low first gear.I have to be careful not to give my Honey whiplash .
 
RustyRatRod said:
I just put a used 625 Street Demon on my 75 F250. 351M, Weiand Action plus, GM style HEI 20* initial and 35 total in by 3000. Exhaust manifolds. I THINK it MIGHT have the Melling, TRW, Elgin, "everybodys" grind that's like 204/214 @ .050, but on a Ford the lift is more because of the 1.73 rocker ratio. .484 and .512.

Anyway, I got the carb in a trade. It needed some repairs. The secondary air door spring was broken. Thermoquad air door spring fits perfectly. Put a kit in it. Cleaned it all up lookin like new.

This thing runs like a bat out of hell now. When that secondary door opens, this big old truck moves. Anyway, I am noticing something a little different from other carburetors and wondered if others running these noticed it too.

There's "not a lot" of the primaries. In other words, the primaries have a kinda short travel. The secondaries come in pretty quick with the pedal travel. I kinda like it. Anybody else notice it?
Click to expand...
Stock converter, RRR ?..
These carbs, are intriguing me....
 
I've been doing a lot of fine tuning on the 750 version. OOTB (for my setup) the primaries were way rich. I actually had to use the smaller primary jets from the 625 jet kit (for my son's car) along with metering rods from the 750 kit in order to get it right. Theses carbs respond to the most incremental changes quite noticably. Only negative I've come across was on the son's 625, the choke plate hung up, actually hyper extended (where it closed and the rear of the plate came out of the opening and hung-up) On the 750 the Ford kickdown arm was hanging up on bigger throttle openings and the throttle then stuck open. I hacked it off and no issues since. Nice carbs, but they can suffer from some niggles that shouldn't occur.Heres a nice article on the carbs, and some tuning advice:. www.chevyhardcore.com/tech-stories/tech-tuning-tips-to-get-the-most-out-of-the-street-demon-carburetor
 
Rusty, do you think there is a difference in spring rates between the Demon secondary air door spring and the TQ one? Maybe that would account for the short pedal before the secondaries open?
 
12many said:
y. Only negative I've come across was on the son's 625, the choke plate hung up, actually hyper extended (where it closed and the rear of the plate came out of the opening and hung-up www.chevyhardcore.com/tech-stories/tech-tuning-tips-to-get-the-most-out-of-the-street-demon-carburetor
Click to expand...
got a 750street demon to replace a 670 holley that replaced my od TQ. Love the demon, responsive like the TQ. I have the same issue with the choke plate, I was going to drill/tap the tower to put in a set screw to act as a stop. The only thing i did was tune the air door.

having some issues with the choke nadjustment, idles well for a few seconds, then runs rich so i have to kick the choke off
 
lil red said:
got a 750street demon to replace a 670 holley that replaced my od TQ. Love the demon, responsive like the TQ. I have the same issue with the choke plate, I was going to drill/tap the tower to put in a set screw to act as a stop. The only thing i did was tune the air door.

having some issues with the choke nadjustment, idles well for a few seconds, then runs rich so i have to kick the choke off
Click to expand...
Simple fix, place a flat washer under the lock nut for the stud. The washer hangs over enough that the choke plate hits it, choke plate not going any further yet it closes as it should when cold.:thumbsup:
 
I have the 750 version which was last running on a mild built 360, I didn't notice the primaries having short travel since the difference in airflow of the bigger one comes solely from bigger primaries, so I didn't need to give it much throttle to get going. I believe the linkage arm that opens the secondary throttle plate is adjustable, have you tried that?
 
DFX 340 Duster said:
Rusty, do you think there is a difference in spring rates between the Demon secondary air door spring and the TQ one? Maybe that would account for the short pedal before the secondaries open?
Click to expand...



if I understand your question right I would say no the spring rate is adjustable and a very important in tuning .
 
RustyRatRod said:
I just put a used 625 Street Demon on my 75 F250. 351M, Weiand Action plus, GM style HEI 20* initial and 35 total in by 3000. Exhaust manifolds. I THINK it MIGHT have the Melling, TRW, Elgin, "everybodys" grind that's like 204/214 @ .050, but on a Ford the lift is more because of the 1.73 rocker ratio. .484 and .512.

Anyway, I got the carb in a trade. It needed some repairs. The secondary air door spring was broken. Thermoquad air door spring fits perfectly. Put a kit in it. Cleaned it all up lookin like new.

This thing runs like a bat out of hell now. When that secondary door opens, this big old truck moves. Anyway, I am noticing something a little different from other carburetors and wondered if others running these noticed it too.

There's "not a lot" of the primaries. In other words, the primaries have a kinda short travel. The secondaries come in pretty quick with the pedal travel. I kinda like it. Anybody else notice it?
Click to expand...

I LOVE Adrianne Boob-Beau!!!! One hot mama from the 70/80's!

Now back to our regular programming!

Marion
 
I have had one since they first come out, it is really a set it and forget it carb, way better than than anything else for driving everyday.
I get 14.5 mpg out of my old 4x4 truck every tank with this carb.
 
I have been running the Street Demon 750 in mine for almost a year now. I love this thing, its like an offspring between a Thermoquad and an AVS.
I had to lean the primaries out quite a bit with rods + jets. (I live at 4500 feet above sea level).
I drove to Louisville, CO and back (506 miles one way) a few weeks ago.
No issues! (other than the alternator going out in a blaze of glory and frying the fusible link plus voltage regulator)
Mileage was 14.3 mpg driving though a 45-50 mph varying crosswind/headwind to about 16 mpg's on flat areas. The best was 17.4 but was a lot of downhill.
This was maintaining between 70-72 mph's which is about 3,000 rpms. Except for construction and other areas that had 60-65 mph speed zones.
I have 3.21 rear gears and 245/60R15 tires. (26.5in diameter)
There is one thing that would've made this trip a little better... A/C! Which is next on the list, I'll have to boost up the charging system to more than what it is now at 65 amps.
 
DFX 340 Duster said:
Rusty, do you think there is a difference in spring rates between the Demon secondary air door spring and the TQ one? Maybe that would account for the short pedal before the secondaries open?
Click to expand...

No. Since that's adjustable, that would have no bearing. I am talking about the throttle blade travel. Not the air door.
 
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