Old folks - 'splain me about the heat riser valve please.

[davepl]

So my truck is set up in what is basically 100% stock configuration, optioned with dual exhaust from the factory with the 402.

On the passenger side I have the heat riser valve. At idle, EVEN AFTER WARMED UP, it stays largely closed and most exhaust from that bank is forced up through the crossover and out the driver's side exhaust.

It's not stuck though, and if you blip the throttle it'll open more. I assume when driving around it's at least partly open based on that.

Still, that seems wrong to me once it's warmed up. I think it's a great idea when cold.

Does anyone know if it should open fully on its own once warm, or just do what it's doing now? So few people keep them in working operation that it's hard to find people who know!

I think the valve is original, so if they wear out, it's definitely time for a new one. But it's loose and moves freely, and the spring still is springy, so unless the spring response changes with age, should be ok.