MBrianB

All,
I just installed an awesome set of chambered exhaust on my little C3. It now backfires (afterfires) a lot.

My AIR injector pump was making noise so I took off the belt and now I don't get the backfire so much.

What can I remove or disconnect in the smog system easily without removing parts and plugging holes in manifolds?

What changes do I have to make to have the engine run better with those items off line?

I also ran the distributor vacuum advance directly to the port on the carb bypassing the vacuum advance controller.

Thanks.

BTW I do not need smog inspection on this year anymore in California.

I hate to remove it all in case a future owner wanted to be OEM.

Easy Mike

AIR only puts oxygen into the exhaust stream to assist with burning gases. I'm not sure it has anything to do with exhaust sound.

I could suggest removing the belt to the AIR pump, but you say you do not want to remove parts. The belt is a part.

hugie82

Removing the belt will help a little. Distributor is a good place to start to find a little power and a k&n air filter will help out in the power department. Your backfiring comes from outside air getting sucked into the exhaust. The tiniest leak on the manifold flange or where pipes connect can cause back fires.

MBrianB

Going through the repair manuals I found that the AIR system pumps air into the exhaust manifolds to make a more complete burn of unspent fuel. When the throttle is lifted the AIR pump is supposed to open to the atmosphere and stop going into the manifolds. When I checked my pump it did not vent through its muffler like it should. That is why I was getting such a loud backfire, like a gun going off.
Actually disconnected two of the clamped joints on the exhaust system near the ends. I mean it was LOUD!

It has been a long time since I worked on an emission vehicle so I thought I would ask if there is anything else I should do.

hugie82

If you're in California be careful. From what I understand they want to see everything in place as it came from the factory. If anything is swapped out, it need that CARB # stamped on it. Good luck. Rock auto is pretty good with air pumps and parts.

TimAT

The AIR pump, as you noted, pumps fresh air into the exhaust for a more complete burn.
The diverter valve has a vacuum line going to it that closes the valve under high vacuum, (off throttle). Make sure that valve is closed, it will stop the fresh air from going into the exhaust even with the belt removed. Also, there is a check valve on the tube that goes into the manifold. Supposed to let air flow to the manifold but not back toward the AIR pump. That one could be stuck open.

SI67

You'd also be a little late. He already took the belt off.

Steve

SI67

What is the vacuum advance controller? I know about the vacuum advance canister on the distributor, but you're obviously talking about something else. I've never heard of that part, but I am unfamiliar with anything newer than '67. Just curious.

Steve

SI67

That used to be the case here, but after a certain car age (I don't know the specifics) it no longer applies. I know I haven't had to smog-cert my '67 for quite a number of years. They've lost interest in the older cars, figuring there aren't enough of them on the road to to be significant in the air pollution picture. Seems like some common sense sneaked into the system!

Steve

Easy Mike

I was trying to play by the OP's rules.

jb78L-82

When I had my AIR pump hooked up (which is long gone now), if I disconnected the vacuum line to the diverter valve with the belt on the AIR pump, when i decelerated, the exhaust would backfire/burble...

MBrianB

The original system is best described here:

http://shop.docrebuild.com/1974Corve...eplacesGM.aspx

Paul L

I'm guessing that the reference is to the TCS (transmission-controlled spark) solenoid and system. I have never figured out how it works so it is gone. I do have the parts.

my 76 ray

If your afterfire is when you are decelerating I had that problem on my '74. What I discovered is that when I had the vacuum advance hooked up to manifold vacuum it would cause afterfire. By hooking it up to the ported vacuum on my carb (aftermarket carb so I don't know if you have one) it eliminated the afterfire.

MBrianB

That's the little bugger. It is for the L82 4 speed 1974. I took the line from the dist to the controller pulled the controller's vacuum line from just behind the fuel filter on the carb and put the dist line there.

Paul L

Just remove the solenoid and connect directly to either manifold vacuum at the carb choke side or the upper left ported side on the carb. My car likes ported strangely despite popular opinion.

MBrianB

Ported? Who'd a thunk it?
Ill try your suggestion. Thanks.

Paul L

It is hard to know what is best for that era. Your L-82 with a manual transmission required an AIR pump both federally and in CA. My L-48 with TH400 did not require an AIR pump federally but did for CA. When you throw all the emissions combos (including the 454) into the pot and stir it who knows what comes out the far end?

outlawkinser

My '74 L82 with manual transmission also likes ported rather than direct vacuum.

Mike

dochorsepower

You might also like the results of blocking off the EGR. The engine has a more lively response when you do. Plug the AIR injector ports, the check valves sometime don't work that well and leak causing more noise.
Yes, '75 and earlier in Cal. don't have to have smog checks.