I drove my recently completed Mach 1 project to the Roundup and also participated in the autocross. I'm running a Summit Racing carburetor which is very similar to the 4100. On my 2nd and 3rd runs, my engine fell on its face right after the start. I think it's a vapor lock issue. Some friends of mine recommended revving the engine a little before the start and that really helped on my 4th run. In fact, I did a bit of a burnout at the start.
Consider Steamboat Springs is between 6,000 and 7,000 feet above sea level. That's a BIG factor for vapor lock issues. Combine that with ethanol in the fuel and it becomes an even bigger problem. There's a gas station on Lincoln Street in Steamboat which sells 100% gasoline. Although the premium is $3.70 a gallon, it would be worth it next time. (My friend who brought his 1970 Boss 429 reported his idle jumped up a full 250 RPM when he ran 100% gasoline.)
Fuel line routing is a critical factor for preventing vapor lock. I think that was my issue. I have an aluminum fuel filter and it's very close to the top of the engine. I'm going to try re-routing that to see if it helps.
Does the car have a phenolic spacer under the carb? If not, that might help. Also, as suggested, definitely check the float levels.
Anyway, I don't think the 4100 is the problem. That's a very good carb used by many a racer for many years.