A little extra information:
Several years ago, right after we bought the remains of Stromberg, we were doing our best to service the various Strombergs.
The larger GMC engines (401's and 478's) used a Stromberg type WWC carb. Wonderful carb but VERY expensive. We had some adapters cast (the WWC uses a trapazoidal flange pattern) to adapt the cheaper Holley 4412 which is about the right size for the 401/478.
We sold 6 of these conversions, and customers were happy (at least with the price, the Holley was never a Stromberg) until the choke pull on the Holleys started BREAKING!!! (seems Holley thought a plastic choke pull would reduce the cost of the carb). They also were not happy with the gas mileage, as it was about half what the Stromberg obtained. They were happy with the power, which was about the same.
Holley wouldn't warrant the carbs due to breakage; but we had three older junkers with the metal choke bracket, which we sent out. When the others came back, we had to refund their purchase price, which we did.
Subsequently, I understand Holley went back to the metal choke pull.
So check the choke pull bracket on your Holley. If it is plastic, treat it VERY gently when pulling on the choke, especially in colder weather.
Jon.
