the 79-80 rx7's had thermal reactors. the rest of the 1st gens had cats. pull the plates that surround the exhaust manifold off. the cloth type pipe that i was referring to connects from the neck on the carb snorkel to the exhaust manifold plate. it is there to draw warm air off the exhaust mani for better cold weather starts. sorry for the confusion. with that said, its the bottom plate that you want to take off from around the exhaust manifold unless the top plate is doing it too. very easy. 8-10mm bolts if im correct. just get the car lifted up on the passenger side, go under and find where the exhaust should hook up to the block and there will be the plates surrounding it.

when it happened to me, it wasn't bad or noticeable when i was driving cuz the intake sucked in most of the smoke. but when i stopped it billowed out of the hood and smelled like musty and wet smoke. the insulation prob wears out and defects from getting wet.

 

Sad... "Thermal Reactor" sounds so cool. Yeah that hose you're talking about confused me a little. Mine's a plastic ribbed one like a hose on a vacuum cleaner and goes from the top of the exhaust manifold plate to the bottom of the nose of the air cleaner (it's also old and cracked in a couple spots). My dad came up this week end and I started it up for him, turned it off after a couple minutes, then about a minute later smoke started coming out and he says it looks like it's coming right out of that hose. So there's just rubber insulation on those plates that's probably burning off? I have a set of 12a headers somewhere that maybe I could put on, the guy who gave them to me made them custom though and it's just a whole bunch of little triangles welded togeather. Plus I don't have an exhaust manifold gasket lying around.

 

its a fibrous, cotton like pad. could prob even be asbestos which would suck cuz i inhaled a whole bunch of it lol. i'd definitely get the headers on when you get to it, its a lot better flow than the exhaust mani. but yea just pop the bottom plate off. it bolts to the exhaust mani if i'm correct. the only reason they are there is to direct heat over the exhaust and up the pipe to the carb. no need to take off the actual manifold so you're not gonna need the exhaust gasket until you decide its time to put the headers on. i'm glad i could help you out with that. as far as i know, i'm the only one that has had that problem.