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Discussion in 'Engine Topic' started by Black78, Mar 8, 2010.
Trying to figure out what this thingamajig is
I believe it works with the heat riser on the exhaust manifold.
Ding, Ding, We have a winner
where can i get replacement? it klanks like crazy when motors runs. diaphram must be shot
Check Classic Industries, Year One, etc... for a heat riser vacuum module (I think that's what its called). I used to have one a while back that I took off my 78 when I put headers on. I think I got rid of it, sorry.
I would test it first to see if it holds vacuum. The vacuum hose, as I recall, runs to a thermal actuator in your intake cooling jacket which either allows vacuum to flow once a certain operating temperature is reached, or cuts it off. I can't remember which way it works, but a close look will tell you. I think it holds the flapper valve open when the engine is warm; not holds it closed when the engine is cold, but I may have that backwards.
If the vacuum can is good, you may only need a new actuator/sensor. That, too, can be tested by seeing if it opens (or closes) only when the engine warms up.
You could also have a bad or disconnected vacuum hose to or from the actuator/temp sensor.
I believe the idea is to restrict exhaust flow to aid in a faster warm-up. The good news is that your flapper valve in the exhaust manifold is apparently not froze-up since you can hear it clanking. However, iirc, there should also be a spring on that flapper to keep it from clanking. If so, it may have broken.
Most guys just pitched the whole assembly. If you need it to look stock for smog regs or show, remove the internal flapper and reassemble. End of clanking, and you won't experience any driveability issue. Just make sure you don't leave a vacuum leak unaddressed.
the flapper isnt clanking. Its the disc.piston in the actuator clanking on the sides of the actuator housing. it does hold a vacuum somewhat, the vac line is perfect, and the spring on the heat riser is fine.
also, the object of this system is that the actuator will close the heat riser when cold forcing the manifold to heat up faster. The heat stove attaches to the top of the passenger manifold. a flexible hose would then run from the heat stove to the factory air cleaner cover and let warm air pass the carb. basically useless if youve removed the factory air cleaner assembly.