If it is a Speed Demon that was produced prior to Holley acquiring them, you may have to call Holley to get it figured out. When Holley acquired Barry Grant, they started laser etching the model number into the flange where the air cleaner assembly sits. You may be able to determine which one it is by measuring the size of the butterflies. Do the end of the fuel bowls say Speed Demon or Road Demon?? I would guess that it is a 650 mechanical secondary, but measuring the butterflies will be the best place to start.

 

There will be a way to identify the carb with what Barry Grant stamped on the carb. They didn’t use traditional part numbers such as Holley, Edelbrock, Carter and Rochester used. A friend that buys and sells a lot of carbs tried to explain their system to me once, but I’ve since forgotten. I’d try YouTube, I have a hunch you will find a video showing how to decipher their system.

Steve R

 

Looks like a 650 Speed Demon. If you want to know for sure, what's the little single digit number by the rear vent on the top. It will either be a 6-7 or 8 and that being 650, 750 or 850, that's how you tell. Mighty Demons use a different numbering system.

 

It looks like a Road Demon or Speed Demon. Try this to figure the size. https://itstillruns.com/can-tell-size-demon-carb-8532411.html

Barry Grant's earliest carbs had hand engraved numbers and descriptions on them. I don't see them on that carb, so it's one of the later builds.

The "p" and "S" distinguish the primary or front bowl from the secondary or rear bowl.

 

I need help identifying my Demon carburetor as well.

 

Find the little number on the sec side above the booster opening and I can tell you what it is.