My 400SB runs great. I have noticed that on deceleration, I can hear and feel a slight popping in my exhaust. It is an internal popping, coming from under the car (muffler???) and not a typical gunshot backfire. Usually occurs when I let up off the gas, and coasting down the highway. The faster I go, and let off, the more harsher the popping gets.

What could this problem be? Should I try higher octane? Do the heads need to be rebuilt? Is it the timing? Any advice or information would be very appreciated.

Thanks,

So-Cal Jack

Sounds like an exhaust leak. If one of the connections show a little soot around them that is the leak. My El Camino is doing that and I can see the leaky joint, just haven't gotten around to fixing it yet.

I figured it would possibly be a leak. I'll have to crawl under and around it to find the area.

Thanks for the info. I'll let you know what I find.

So-cal Jack

Sometimes, a bad EGR valve will cause backfiring. I doubt if your car has one though.

If you've got the idle circuits on the carb tuned a bit on the rich side, that could cause extra fuel to be dumping and collecting in the exhaust. I think the popping you're hearing is the extra gas igniting on a hot spot in the exhaust. Have you pulled the plugs to check that your fuel mixture is set properly?

No I haven't checked my plugs yet. I was going to pull my carb, and see if it needed to be rebuilt. So far, all that I've heard was that my carb needed either an adjustment or rebuild.

I'll definitely look into the settings to see if it's too rich.

thanks for the advice....

so-cal Jack