I have a 1972 LT - 1 in show condition. It has it's full smog system intact. In between shifts or during high RPM deceleration the exhaust makes popping noises. I thought it may be an exhaust gasket leak - swapped gaskets - still pops. Then...I changed the smog tubes with NOS tubes (they did have a small leak) - still pops. Carburetor is super dialed in (Lars), Ignition timing is spot on (Lars technique).
Took off smog pump belt - pops gone. Just purchased NOS check valves (don't have yet). If the exhaust still pops after the check valve installation, I want to make the pump inoperative...but I want it to look stock, with the belt installed.
Anyone done this? As this is a show ready vehicle - I want to leave the smog equipment installed.

 

Have you tried a half turn OUT on the Idle mixture screws?

 

My 72 LT-1 used to do the same thing and it turned out to be a faulty diverter valve. You can find them on EBay but you won’t like the price. I bought a remanufactured one that has worked fine for several years, same seller still has them for sale there.

 

Diverter valve is not working. Probably won't hold a vacuum.

You can get the valve fixed but maybe you would be OK with a disabled smog system? I would not gut the vanes out of the pump.

What i did - removed the tree extensions from the manifolds and put pan head screws into the trees, pointy end first to take up the space, and block the heat from traveling up the trees. I installed a non-original rubber hose from the pump to the trees with some vent holes on the underside to relieve pressure from the pump. Not visible from the top. The pump still has the vanes. Looks right but does not cause popping between gears.

 

Remove the vanes in the pump.

Its very easy to do. Many owners disable the system but leave it intact for the very reason you describe.

 

If you want a tutorial on removing the pump veins just google pacecarjeff. Under de-veining a smog pump. I used his instructions back when i deveined a pump. Very easy to do, IF you have a good turning pump and one that isn’t froze up or has a bad bearing. I actually have two complete sets for my ‘73. One nonfunctional and the other functional.
He also sells all or most other smog items like the check valves and diverter valves etc. He might even be a member of this forum.
JP

 

Thanks to all for the most excellent advice. I'll double check my diverter valve...if need be, I'll order it from Pace Car Jeff.

 

In todays world with tuner turbos and their stupid pop-off valves you fit right in.

 

I did this on my 73. Not difficult but it took some time to do. Looks completely stock but without the drag of the pump. I also used pipe plugs in the ex manifolds so the SMOG system is now completely disabled. Well worth it.

 

Here in the Northern Virginia area we have hundreds of Asian (Wannabe RACE) cars that pop like crazy while decelerating. According to one owner they actually buy a new "Chip" just to make the car Pop under deceleration. I even saw a Asian car blowing flames out of the exhaust while shifting going down Rt.50. I am not sure I want a car blowing flames out the exhaust but some fools think it is cool. It kind of reminds me of the guy who walks around playing the TUBA near George mason University who can shoot big flames out of the TUBA bell, WHY??

My C3 does not have anything but a PCV and that is the extent of the emissions system. I have been told that being an early 1968 that it should have the air pump and the tubes into the exhaust manifolds. I currently have long tube headers attached to a Chambered Exhaust.

I also have a 1988 C4 Coupe with it's L98 engine. On that car I have and will maintain the emissions system operational even though the emissions inspections are no longer applicable to the 1988 models in Virginia. During the Annual Safety inspections they verify that the catalytic converter is Physically there. The car runs better with the complete emissions system and will perform better for longer. It also gets better mileage when the emissions are working properly. Instead of getting rid of the catalytic converter I put a slightly bigger unit on in it's place that flows more and keeps the exhaust cleaner.

People like to remove the C4's EGR system and then the engine starts pinging because of the higher combustion chamber temperatures. Now that engine will NEED High Octane fuel where as my C4 would run fine on 87 octane with a functional EGR. When I bought the car it had a faulty Knock sensor and the timing was being retarded the whole time I was driving it. The engine runs a lot better with full timing so if you have a knock sensor then you should test it to be sure it works. Simply tap (don't break anything) with a metal object (like a wrench) on the block or the cylinder head and the idle should drop a hair letting you the sensor is working properly.

My general feeling is "If it ain't broke, don't fix it" applies to Corvettes as well as any other vehicle I use on the highways. I do like to do the required maintenance on the cars but I like to keep them safe, legal and clean running!

 

That’s where I got mine, good guy to deal with.