I bought this carb about a year ago, brand new. Have not been doing much driving until lately though. This is my experience so far. Since it's a different design my old Moroso air cleaner hit the choke, so you either have to get a spacer to bring the air cleaner up a bit, or get the Street Demon air cleaner. The fast idle adjustment for the choke is accessed thru a hole in the back of the choke, facing the firewall. It's very hard to adjust without removing the carb.
Out of the box it has excellent part throttle response. The engine feels really happy and responsive. Easing into full throttle it pulls very hard. Great driveability so far! Returning to Idle it has some binding/sticking issue. I set it up to idle at 800rpm, I noticed it dropped to 600rpm sometimes. I removed my linkage and air cleaner and it's still there. This is after it has come of the fast idle cam. Pushing the linkage down with my fingers brought to it 600 rpm. I took the carb of to check the transfer slot and it was almost not visible. Set it to a square and opened and closed the throttle many times to get a feel and check for binding. It seemed alright but after installing it the problem remains. I have a fresh pair of return springs installed as manual suggest. So I need to take a closer look at this.
Driving it in a more spirited manner it has a bog when you stomp on it.
I borrowed my friends Innovate LM-1 wideband. The idle mixture was rich so I set it to around 14.7. That made it a bit leaner driving in low rpm's also. I get 12.5 on the highway at 2500 rpm. It has a bad lean bog going into WOT fast.
I don't have any jets or metering rods to swap as I just started tuning the carb. But I aim to lean it out a bit on the primarys. At WOT I got around 13, that's pretty good right? The Demon comes with 80 jets for the secondaries.
The secondaries have a air valve door to make the transition smooth. From manual: "The secondary air valve door is designed to dampen the transition from primary to secondary operation. Controlled by a torsion spring, the secondary air valve door is tunable to permit seamless primary to secondary throttle response regardless of the throttle rate opening. As an example, you experience a hesitation or backfire when the secondaries open. This means the secondary air door is opening to quickly, so it is necessary to adjust the door tighter (counterclockwise) until the hesitation disappears."
I've tuned this in small incremental steps to cure my lean bog going hard WOT. But the bog remains. So I moved the accelerator pump connection rod to the top position to give it larger pump shot. The bog remains. As I mentioned I dont have any jets, metering rods and accelerator pump nozzles to swap at this time.
I have a Pertronix Ignitor II & Flame Thrower coil. My initial is around 20-23. There is some lope in my cam so it's hard to say exactly. Total is locked to 36 and it's all in at around 2500 rpm. The motor seems happy, don't kick back, don't ping and don't get to hot.
I have checked float levels and they are spot on. I have checked the jets and nozzles for dirt.
So if I can get rid of the bog I will be a happy camper. Because I really like the throttle response of this Street Demon Carb. Compared to my Holley and Edelbrock I've had before this just feels much better for my combo. I'm not saying the other brands are bad in any way.
So I write this to get some tuning tips for the lean bog and just share my experience with the carb for anybody looking into getting one.
So this is my combo:
1970 Plymouth Duster
273 Commando - 1965
Compression: 10.5:1 (well this I dont know for sure, it's a true commando though).
Heads: Gasket matched and ported
Cam: Solid lifter Comp Cams Magnum 282S - 282/282 Lift 495/495 Beehive Springs
Edelbrock D4B intake / Street Demon 625 carb
PerTronix Ignitor II Billet distributer & Flame Thrower coil - Taylor plugwires
Hooker Headers
2.5" Dual Exhaust / Super 44 Flowmaster
727 auto / Shift Kit
10" Turbo Action Street "S-800" (17805SMED) converter (3200 stall)
8 3/4 - 3.55 - SureGrip
6 leaf - leaf springs from Espo
B&M Quicksilver Shifter
BF Goodrich 245/60-14 out back
