Engine power issues ANY ideas??? Can heat riser butterfly cause issues ?

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Jul 19, 2021
Blacksburg VA
I apologize for lack of details, but that's what has me stumped....
Resurrected a "new" FJ60 that had sat for a year or more. Minimal effort, no real "clean up" just good fuel, battery, oil level and she was running like a top. About 500 miles in I'm on my way to work and thought "hmmmm feels weak pulling this moderate grade." It was noticeably different and then 1/2 mile later it starts a clacking sound. Pull over, sound's gone, weigh options and drive to work.
Still felt weak ish. Fiddle at lunch can't find any issues, down road and back seems fine. Leave at the end of the day and 1 mile down the road definite power loss and noise returns. I turn around (noise goes away ) and leave truck at work.
I pulled the intake and valve cover, can't find anything out of place, check valve clearance only adjust 2 valves a few thou.

No better.
truck came to me with electric fuel pump, poor plumbing, and 2 fuel filters.
I pulled the mechanical pump from another working truck and re-plumbed properly. I left the primary filter unchanged - fj40 style clear plastic fuel filter that doesn't look dirty, could it be? fuel supply issue wouldn't cause a noise, right?

I addressed significant exhaust leak at main down pipe below heat riser. Notice the heat riser is completely loose in the housing and no longer connected to the shaft and spring. Left it for now. Could that flapper, pretty much completely floating free and off center, cause power issues?

I drive the truck home tonight and once briefly thought I had the clacking noise but definitely feel it is down on power.

Anything ???
Not sure about your clacking noise. The first thing I check with a noticeable power loss is the secondary diaphragm. I have inspected 4 used carbs over the last few years and they all had perished useless diaphragms. It's very common.
Only way to find out if the heat control valve is FUBAR is remove the manifold and separate it. (Unfortunately).
The machine shop I took my manifold to several years ago worked on a lot of land cruiser engines and manifolds. Every cruiser manifold that came through his shop, he removed the heat control flapper valve entirely as a standard procedure when overhauling them.

If the flapper gets stuck in the “cold” position, the AF mixture getting sucked into the cylinders will be overheated (and the intake manifold can crack)
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