I have been working on getting a Street Demon 625 dialed in and I thought I would share what I have learned so other people might have a little easier time. My other carb is a Street Avenger 670 which also took a while to dial in. I just tried the Street Demon out of curiosity.
I have a '67 Dart with the drive train from a '72 Duster. It is a 340 bored 30 over with a cam that is just about stock in specs, it has Mopar aluminum heads and the standard electronic ignition upgrades that uses the silver box. The transmission is a 727 and the rear end is an 8 3/4 with 323 gears.
I installed an oxygen sensor and gauge so I could track the AFR. Initially the Street Demon ran very rich out of the box. Idle was about 10.5 and cruising was about 11.5.
I got the tuning kit and after reading what little I could find on forums I found what I thought was a reasonable match on a Ford forum describing a Mustang with a 351. He indicated that he stepped down the primary jetting from 80 to 76 so I took the carb apart and did that. That resulted in much better cruising with an AFR about 14, but there was a huge stumble if you were going at low RPM (20 MPH or so) and stomped on the gas.
I talked to Holley support and they suggested that I put a bigger squirter in it. It comes with a 31 and I upped that to a 35, then a 37, and finally a 40. That helped a bit, but was not the total answer.
I also swapped metering rods around until I settled on .058 x .052. If I ease into acceleration it runs fine. Stomping on it has a bit of a stumble sometimes. Running smaller metering rods gets better, but the AFR is 12.5 with .058 x .050 or 12 with .056 x .048 rods. I would rather be running at the 13 - 13.3 that I get with the .058 x .052 rods.
The idle runs about 13.3 with 2 full turns out and 1/4 turn back to lean and I was happy for that. My guess is that it came from the factory with 3 full turns out so be so rich.
I also adjusted the secondary invocation a lot so that it is seamless. It took a lot of pedal pressure to get the secondaries to kick in out of the box.
In no case could I get it to light up from a dead stop idle. It just stalled out of hand. I can live without doing that.
As the ads say the throttle response is very good. The idle is smooth. It makes for a pleasant ride if your wife is along. When you really want to get on it you won't be as happy. Maybe more tuning would fix that, but I have been doing a lot of trial and error.
The Street Avenger 670 on the other hand will light up the tires from a dead stop idle all day long. And with some tuning I got all the stumbles out so it runs great. So I would put it back on if I want more responsiveness. I will run the Street Demon for a while out of curiosity before I make any changes.
In tuning the Street Avenger I got the float to the bottom of the sight hole. I swapped out jets until I had the best response with 68's for primary. I adjusted squirters until a 32 worked best. I also made sure there was no play in the accelerator pump circuit. I still had a mild off idle stumble with a slow start even though stomping on it lit up the tires. The belle of the ball was the blue carb cam. I replaced the orange cam that came with the carb with the blue one and all stumbles went away. I also adjusted the choke duration so it stayed on a little longer.
I hope this information is helpful.
I have a '67 Dart with the drive train from a '72 Duster. It is a 340 bored 30 over with a cam that is just about stock in specs, it has Mopar aluminum heads and the standard electronic ignition upgrades that uses the silver box. The transmission is a 727 and the rear end is an 8 3/4 with 323 gears.
I installed an oxygen sensor and gauge so I could track the AFR. Initially the Street Demon ran very rich out of the box. Idle was about 10.5 and cruising was about 11.5.
I got the tuning kit and after reading what little I could find on forums I found what I thought was a reasonable match on a Ford forum describing a Mustang with a 351. He indicated that he stepped down the primary jetting from 80 to 76 so I took the carb apart and did that. That resulted in much better cruising with an AFR about 14, but there was a huge stumble if you were going at low RPM (20 MPH or so) and stomped on the gas.
I talked to Holley support and they suggested that I put a bigger squirter in it. It comes with a 31 and I upped that to a 35, then a 37, and finally a 40. That helped a bit, but was not the total answer.
I also swapped metering rods around until I settled on .058 x .052. If I ease into acceleration it runs fine. Stomping on it has a bit of a stumble sometimes. Running smaller metering rods gets better, but the AFR is 12.5 with .058 x .050 or 12 with .056 x .048 rods. I would rather be running at the 13 - 13.3 that I get with the .058 x .052 rods.
The idle runs about 13.3 with 2 full turns out and 1/4 turn back to lean and I was happy for that. My guess is that it came from the factory with 3 full turns out so be so rich.
I also adjusted the secondary invocation a lot so that it is seamless. It took a lot of pedal pressure to get the secondaries to kick in out of the box.
In no case could I get it to light up from a dead stop idle. It just stalled out of hand. I can live without doing that.
As the ads say the throttle response is very good. The idle is smooth. It makes for a pleasant ride if your wife is along. When you really want to get on it you won't be as happy. Maybe more tuning would fix that, but I have been doing a lot of trial and error.
The Street Avenger 670 on the other hand will light up the tires from a dead stop idle all day long. And with some tuning I got all the stumbles out so it runs great. So I would put it back on if I want more responsiveness. I will run the Street Demon for a while out of curiosity before I make any changes.
In tuning the Street Avenger I got the float to the bottom of the sight hole. I swapped out jets until I had the best response with 68's for primary. I adjusted squirters until a 32 worked best. I also made sure there was no play in the accelerator pump circuit. I still had a mild off idle stumble with a slow start even though stomping on it lit up the tires. The belle of the ball was the blue carb cam. I replaced the orange cam that came with the carb with the blue one and all stumbles went away. I also adjusted the choke duration so it stayed on a little longer.
I hope this information is helpful.
