i have a 82 gtv6 (under resto)not doing any work on engine but one day when i tried to start it there was a BANG!.After changing my undies i saw that the plenum had popped off.Put it back on but BANG!? Any ideas guys
yes, it's the thing on top between the cam covers but it doesn't have 6C on it on a GTV6. The plenum pop can indeed happen when the timing is out. When you say you put the plenum back on again, how did you do that?
I've seen this before. Check that your throttle is closing fully. There is an adjustable screw-stop on the throttle butterfly. If this is not closing then you get backfiring. It normally happens when this is used to adjust idle speed, rather than adjusting the hose that goes into the side of the plenum.
You might also have an air leak somewhere. There is a great tune up guide for 116 V6 cars. It is at www.oldebottles.com look under italian cars page three. Greg Gordon put up this page, It is excellent.