Street Demon 625 - tuning results with AFR monitor
 

Spent the day tuning the Street Demon 625 on my ‘68 Firebird. The engine is 8.9:1 CR with a Pertronix HEI distributor (18 deg. initial + 15 deg. manifold vacuum advance). Here’s what I got today:

> 60/52 METERING RODS
> SILVER METERING ROD SPRINGS (8” VAC)
> PRIMARY JET: 78
> SECONDARY JET: 80
> IDLE MIXTURE SCREWS 2 ⅛ TURNS OUT

> IDLE VACUUM: 16” PARKED, 12.5” DRIVE
> IDLE AFR: 13.8 PARKED, 13.5 DRIVE
> IDLE RPM: 950 PARKED, 750 DRIVE

> 13.6: AFR CRUISE
> 13.3: AFR PART THROTTLE
> 12.1: AFR HEAVY THROTTLE
> 13.0: AFR W.O.T.

I have one issue with the gas pedal, - I’m not getting full motion and not getting to WOT as a result. I need to solve that problem before I can focus on the WOT AFR. I’m also thinking about trying the 58/52 metering rods to see how it affects the cruise & part throttle AFR’s.

Are you running a stock air filter assy?
If not then what size air filter are you running, and is it a drop base style?

To get more throttle opening sooner with less pedal travel ( which sounds like your issue) you need to lower your cable attachment point closer to the carbs throttle shaft.

The cruise AFR is way too rich. Shoot for at least 15 or 16:1 at part throttle cruise in top gear.

He may only be able to get to that ratio in the correct way with a lighter power piston spring seeing as what his close to full throttle ratio is.

Hey Steve. I'm using Demon's drop base air filter to get the proper clearance for the linkage. But regarding the attachment point, I was thinking going the other direction? Wouldn't I need to move the cable attachment point farther so that I get an increase in the arc?

I currently have #78 primary jets and 60/52 metering rods. The next size leaner would be 62/54 rods. That would lean the cruise & part throttle mixture by about 11%; the heavy throttle mixture would lean by about 8%. Not sure if I want to go there?

I was recently working on my buddies 71 Chevrolet pickup. It has one of those fancy looking Edelbrock bullet top air cleaner assy's.

I do all the work on it. The pickup came this way. I got the Q-Jet dialed in with Cliffs help. I noticed that it was not getting full throttle.
Well, past about 2/3 throttle, the rod end of t h e accelerator arm was touching the underside of the air cleaner base. I ground most of the end of the a rm down, easily leaving enough metal there to support the inner hole(the one you should ONLY be using. No problem after repair.