73 B.B. Smog sys troubles

[Jack Trissel]

I have installed the complete smog system on my 73 Big Block. It pops through the exhaust when I let off the gas. It doesn't do it when I disconnect one of the hoses from the diverter valve.Any ideals what the problem is. I suspect the diverter valve. If so where might I be able to get one.
All insight is greatly appreciated.
Jack Trissel
Member #222847

[Harmon C.]

Re: 73 B.B. Smog sys troubles

Jack
I chased the same problem in my 73 454. It can be stoped by pluging the exhaust manifold holes and gutting the pump. Poping in the exhaust is something I have read they did when they were new. A 190 diverter valve will cost big bucks.

Lyle

[John H.]

Re: 73 B.B. Smog sys troubles

Jack -

"Popping" on over-run on an A.I.R. car is normally the signal that the diaphragm has failed in the diverter valve; when the diaphragm fails (and they all do eventually), the valve defaults to full open, which directs pump output to the exhaust manifolds 100% of the time, causing the "popping". A failed diaphragm also results in a major vacuum leak through the signal hose to the diverter valve.

You can either repair the diverter valve, or gut the pump and plug the holes in the exhaust manifolds as Lyle mentioned.

[Joe L.]

Re: 73 B.B. Smog sys troubles

Jack-----

I'd say that it depends on just how much "popping" there is. My 1969 with small block exhibited some degree of de-celleration "popping" since the day it was new. My 1966 and 1968 Chevelle SS 396's that I purchased new once-upon-a-time did the same thing, too (both had AIR).

So, it really depends just how much "popping" there is and that's really hard to quantify.

Anyway, as Lyle and John described, it could also be a failed diverter valve. These valves were never meant to be serviced, but, "due to popular demand", there are folks out there like Bill Hodel that may be able to repair your valve.

Finding a new one will be VERY expensive. Perhaps, $500, or more, for an NOS example.