I have some recent experience trying to get a Street Demon 750 to run well on one of my Mopars. The following is my observation/opinions. The motor is a mild build 400, cold Edlebrock performer intake and E-street heads. Out of the box it was jetted pretty close for this combo but accelerator pump didn’t seem to be working correctly. Wound up having to open it up, found small gaps in lip of the acc pump the lip seal and a tear in the Holley umbrella style check valve. After replacing those parts the pump worked better but still needed some larger nozzle tuning to resolve some slight residual hesitation.

No trouble height wise as a Thermoquad replacement but required extensive throttle lever modifications to retain the original throttle cable, throttle pressure linkage components, and correct overall geometry. The Mopar throttle pin adaptor designed for the Street Demon and installed on the “universal” throttle lever on the Street Demon, was useless in avoiding the extensive mods. Plumbing for bowl vent and charcoal canister purge are not present, as with most universal aftermarket carbs.

Could never get the choke tuned correctly for decent cold start & run. The factory dual snorkel air cleaner had no issues with the choke housing. The documentation that came with Street Demon refers to possible interference with the choke linkage near the air horn and factory style air cleaners. There is nothing the locate, or center, the lower air cleaner other than the air cleaner stud. I could see where the air cleaner could shift out of place and contact the linage.

Another irritating issue was the “goggle” valve, secondary throttle blade, binding in its bore requiring excessive throttle pressure to overcome periodically, especially on first use after warm-up. Tried to reseat the throttle blade on its shaft to correct, helped a little but never resolved the issue completely.

Overall tolerances of the various components are not anything close to the Thermoquad, when in good shape, or new Holleys, ended up going back to the best Thermoquad I have. While a bit complex by comparison, with parts that are hard to come by now, a correctly tuned Thermoquad, in good shape, is hard to beat for performance and all-around drivability.

Holley still does make a spread bore replacement but it’s a 650 CFM vacuum secondary GM replacement design with a universal throttle lever. Ran one of those too, good drivability overall, just not same full throttle punch IMHO. The Mopar specific models are now long out of production.

BTW, I have the Street Demon 750 and all the extra tuning parts for it currently are on E-bay should there be someone here who would care to take it on. Priced well below what I have in it.

Street Demon 750