The Stovebolt Site Forums The Shop Area The HiPo Shop 350 SBC Bad Backfire Thru exhaust

Fired it up after sitting for a while and this sucker was backfiring awful, really on left side. Has a 4 bbl Edelbrock. Jerry once told me that water can accumulate under the dist cap. I checked, no water. No points. Double checked the timing, it was a little advanced, about 16 deg with no vac., set it back to 10 deg with vac can on dist unplugged and vac gauge on carb vac inlet. Also double checked TDC on no 1. All square. Still backfiring like crazy. Compression test, all 170 psi +/- dry. Wet all about 20 higher. Plugs are gassy, way too rich. Now to idle air adj. Start, still backfire badly. Adjust idle screw to 650 rpm, lean out right side idle mix screw, when rpm increases by 40, adjust idle screw back to 650. Repeat right and left side until idles at 650 and when lean out idle mix reduces rpm. Now backfire stops. Tighten dist hook vac can back up go for a drive, no backfire. About 30 deg total advance at 2000 rpm. I forgot to pull plugs to see if they are still wet and running rich. What do you guys think was causing the backfire?