'76 tuning/timing question

I've got a '76 L-48, 4-spd, stock except for the exhaust. The new exhaust is a true dual setup, 2 1/2" with magnaflow mufflers. I love the performance and sound, but under deceleration and compression
braking I get those light backfires and pops (sounds like a ratty old Ford with glasspacks) through the pipes. Anything I can do to eliminate those? I've got the timing set at 8 degrees BTDC now, should I play around with it either direction? Any way to richen the idle mixture a bit with a stock emissions Q-jet? I've never checked the compression on this motor, I suppose it could be a burned valve or something and I just didn't notice it with the single exhaust. It runs pretty good otherwise, though.
Dave
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Do you have an equalizer, (H), pipe on it?
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Dad
05 C6 Silver/Red 6spd Z51
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Dad wrote:

No H-pipe, would that help? The exhaust is from a catalog (labeled "for off-road use only") so I'd have to get a shop to weld a pipe in. Not sure most shops would do it since I'm missing the cat(s). Any way to compensate for the lack of an equalizer?
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Can't guarantee it would but my '98 C5 with the Corsa Indy mufflers had the popping and a motorboat sound until I opened up the crossover pipe. The C6 is the same way but I haven't taken the time to open up the crossover on it to say that it will do it every time. On the other side of the coin the '72 don't have the popping and it don't have a crossover. Of course it don't run as hot as the later cars do. Sorry, not much help, you might have to fish around a bit to see what works after you make sure it is tuned properly.
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Dad
05 C6 Silver/Red 6spd Z51
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My guess is an exhaust leak upstream around the manifolds. If air is drawn in it will pop. Speaking of air, what did you do to the smog pump and AIR system?
Al
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should
runs
My '77 made noises like that. It turned out to be the check valves in the exhaust lines from the pump, but I doubt you have those in yours. Nevermind.
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should
runs
Wait, I had you mixed up. You have the '76. Take a look at the pump and the lines that go down to your exhaust manifolds. If one of the check valves freezes up, it will cause the car to backfire for a while, until it burns a hole in the line anyway. There's a check valve on a line leading to each manifold.
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Actually, some non-Calif, L-48, 76's did not have smog pumps. I'm one of those lucky ones - so that's not the problem. It does have EGR, however. I'll do some investigating about an exhaust leak. When I was putting on the exhaust system, I broke a stud in the right side exhaust manifold so I had to remove it. It's possible that there is a leak now. I did not use a gasket, (per stock and advice of a Corvette shop). Any good ways to check for leaks? Should I use a gasket? Thanks for the posts.
Dave
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My 75 L48 did this also. The car had 40k original miles when we got it four years ago. Someone had removed the pump, the cat converter, and it has true dual exhaust. I always thought the popping on compression was caused by one of those changes. But it ran great so I figured, what the heck.
But early this year, it backfired through the carb when it was cold and ran really badly for a few miles afterward. It turned out that it was the vacuum advance. It was locked full advance. We got that fixed and the popping through the exhaust on compression stopped (for a while). It started popping again and this time, the distributor got fully rebuilt. Problem has not come back.
Bill - 75 and 02 coupes.

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My distributor is brand new and it made the same popping sounds with the old one as well, so that's probably not it. I still may try to play around with the base timing a little bit, but I am wondering now if it's an exhaust leak around the manifold. Hope I don't have to take it off since it was a bear the first time - A.C. compressor is in the way.
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