Re: red hot exhaust manifold?
Start by having a look at your plugs.
The heat in the manifold is because excess gas is getting burned there instead of in the engine. For some reason all the fuel is not burning in the combustion chamber
I'd bet the plugs are Split Fires, Bosch, Platinums, or some other "one size fits all" Mickey Mouse plugs that the engine wasn't made to run with. What are the chances plugs that fit everything from a Yugo to a tractor that "fit in the hole" are the right ones for your vehicle? Ask your wife how she likes "one size fits all" clothes.
Use the exact same brand and part number the engine was designed around. It's not just a matter of hole size and threads, but heat range (that in itself has many many variables - mixture, compression, gap, R's etc,) indexing, reach, and the ability of the plug to withstand certain other things, like combustion impacts. They are not all the same!
The plugs got too hot, started misfiring, allowing unburned fuel to exit into the manifold and burn there.
After it cooled down it runs again, but may misfire sooner.
Hopefully you didn't melt the tops of the pistons too much, but that's very common when using junk.
If they are the correct plugs in it that the engine designers wanted and it did it, look for retarded or excessivly advanced timing or fuel. Too early a spark, or a too late one will cause chamber temps to skyrocket, frying the plugs and causing the misfire.
Too lean will cause unburned fuel to exit, causing the hot manifold and misfire.
Too rich most likely would get the manifold hot, but not cause the misfire unless it's super super rich.
A timing chain that's slipped will be very hard, if not impossible to start. And you'll hear it crank way too fast.
Let us know what you find.