the original manifolds don't necessarily need the heat flapper to work, as long as it isn't stuck in the "heat" position, that creates some really weird issues. I ran my truck for 20 years with the heat riser broken and had no idea I even had a problem.
Ditto here. Ran my '52 216 for years before I knew what that spring was for.
The thing is though, it took a lot of choke and a strong pull on the throttle cable to keep it running for quite a while after start up when it was cold out. Not the case after I freed it up and put on a new spring (especially after I put the spring on the right way
).
