78sc CIS question
 

I bought a 78 sc 3.0. Car runs great. My question is at startup it fast idles for a minute or two before it slows down. The PO said it was because the mixture had been adjusted because it did not yet have a pop valve. He gave me a box of reciepts with the car. He or someone had bought an airbox for it once. I have been doing the updates and have the valve (not installed yet) So what it the whole truth to the fast idle thing? The car ran good enough that I wasn't going to let that convince me to not buy it.

Your description reflects normal operating sequence for a cold start. When the engine is cold, the Auxiliary Air Regulator produces a fast idle for a few minutes, then returns the idle to normal. The colder the weather, the longer the fast idle duration.

My 78 displays a wide variety of behaviours on start up. Sometimes it's just start and go. Sometimes it revs several times. It runs great once it settles down. Don't worry about it.

I agree with Brian, your '78 is exhibiting perfecty normal cold start operation ("cold" just means less than operating temp.). Regardless of what the PO told you, your car is performing normally.

Do install the "pop-off" valve (there's a very good write-up on the procedure on this site). Again, regardless of what the PO told you, adjusting the mixture will not save you from a "backfire" and a cracked air-box. The pop-off valve will, at least, save the air-box.

Jerry M
'78 SC