Allright olds exprts..looking to replace Lh exhaust mani on my 68 cutlass s has 350..went to that great olds graveyard Desert Auto in phx.& they r trying to sell me a mani but the valve? & spring r missing/or welded?off or open on the extreme lower rt corner of manifold. What does that sensor or ? Do? Can I do without or demand another more complete mani? Jackalack

 

Mine has a small post & a spring mechanism the junkyard replacement is missing broken/cut off

 

that thing sucks anyway.
run it without the flapper door

 

That thing is the heat riser valve and it is closed when the motor is cold forcing hot air under the carb to help with better warm-up running and the curly spring thing is a bi-metal strip that relaxes when things warm up and the valve opens slowly or wide open depending on your foot... I have hedders so I don't have that problem... but I am still looking for a repair kit for my convert

 

Cool,Thanks gents!Now if I can just get my mani off w-out snapping off any bolts!

 

We welded or brazed (the mechanics actually, the real kind that could fix things) those open and put manual chokes on cars with heat risers reguarly when I worked at one of several gas stations in the 70's. All I know is the automatic chokes that worked off a heat stove or tube or whatever they had wouldn't work right afterwards, maybe from carbon clogging up the crossover or not enough heat?
Me was grease monkey, no touch car engine, only oil filler cap and drain plug. Me only use two inch long wrench or me tighten plug too much and strip.

I've found the exhaust manifold bolts come out a lot easier if the engines warm, the hotter the better. I use anti-seize when I put them back together, you never plan on ever having to take them out again.