new jets in. backfiring

Hey everyone, I just installed and drove my '76 with 200 air correctors and 140 mains. There is undoubtedly more power and driveability is better, but the car has the occasional LARGE backfire on decelleration. It does not happen often, but it does happen. I changed the mains back to 135 and the backfiring went away, but I lost power. I am now considering placing my 220 air correctors with the 140 main in hopes to leaning out that large mixture. I do not want to shoot in the dark here, so can anyone offer any insight?

thanks- john

 

I spoke with Mike at Pierce, and had I gone his route, the backfiring would have been far worse. Mike suggested I go with 190 air correctors and 145 mains. I chose a less extreme setup and am still getting backfiring on decel. Should I stick with the 200 a/c and 140 main, but open up my plug gap a bit?

 

I am changing the jets due to an incredibly lean mixture. As in, over 5.5k, it is over 15.5:1 a/f ratio and above that, it only gets worse. The carburetors were rebuilt last summer and the manifold gaskets were changed. There are no air leaks anywhere. The ignition system is in great shape too.

 

Update. Changed to bp5es plugs and it is much better, but I am worried about using such a hot plug all the time. It gets *really* hot in Las Vegas and I am not a fan of overheating, SHould I stick with the bp6es plugs, but upgrades my coils for a fatter spark?