Fred, The jetting could certainly be the cause of your lackluster performance. If it's too rich, it would probably feel flat like you describe. If it was too lean, you'd probably get some popping out the exhaust or backfiring through the carb, or you'd at least feel some surging at cruise.
If you're pretty certain that the old carb had 72/70 getting, that would be a good place to start. It seems odd to me that your primaries are larger -- but if it worked for you, that's what matters. Another option might be to find a good dyno shop in your area. They can hook your car up, stick a wide-band O2 sensor in the tailpipe and they can show you exactly where you are rich or lean, and by how much. It's not expensive. I put my car on one last summer to get a baseline before my EFI swap and it cost me $85, making 4 pulls. -Dave -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Fred Dowaliby Sent: Saturday, June 25, 2005 9:34 AM To: The Chevelle Mailing List Subject: [Chevelle-list] 454 carbs Hi Folks, I am once again in need of your expertise and advice, this time re: carburetor selection and tuning. My car is a '68 Chevelle based 32 Ford street rod, 454/th400 with 3:08 rear. I estimate it weighs about 2800 lbs. Pertinent engine vitals: flat top pistons, Edelbrock Performer RPM heads, air gap intake, Comp Cams CB 280H-10 cam. The stall converter is 2200. I am currently using a new out of the box Holley 750 dbl pumper carb. I have tried a Speed Demon 750 vacum secondary. Both have resulted in lackluster performance. There is no bog, they just don't have any punch. My comparison is the carb I was using (never should have sold it!), an older Holley 750 dbl pumper. That thing used to run like a beast! I replaced it with the Demon because it just looked grungy, I got sucked into how pretty the demons looked, and I wanted to "clean up" the engine. I then replaced the Demon with the Holley thinking I should have stuck with mechanical secondaries like worked well before. This resulted in the same lackluster performance. I made the mistake of breaking the rule "If it ain't broke don't fix it!". I am at a point where I just don't know what to do. Is a 750 big enough for this engine? Should I start playing with the main jets? I don't know what's in there now, but I recall the old one had #72/#70 for primary/secondary. I don't have any experience with carb innards. Should I look for a trustworthy carb expert/shop? Thanks for your help, Fred Dowaliby
