What will make a B & S 24 hp. engine at full throttle start backfiring out of exhaust and carburator.

SOURCE: valve noise

Hi you can set them to 4 thou it should quiet them down pretty much

SOURCE: Honda GX160 Valve Guide Displaced

You may not need to replace the head but a new valve guide may be called for. That will require the proper tool for installing it, so it runs in line with the valve stem.

SOURCE: Cleaned the Briggs & Stratton Riding Lawn

kehmahcliff:
It looks like that your valves need to be maintenanced. This can be done by small engine repair shops. They should have the proper tools.

Also the "timing" of the spark and the fuel injection could be a problem. I hope this helped you.

Greetings Joe

SOURCE: i have a 17hp briggs and stratton vertical intek

adjustment with 4000 feeler gauge
adjust top valve when the bottom valve is fully compressed and than with the top valve fully compressed adjust the bottom valve the same way.
very easy But remember to losen the center tork screw before adjusting the rocker arm nut

SOURCE: 17.5 briggs intek backfiring thru carb wont start

Easy things to check, flywheel key, make sure it is not broken, check the coil gap to the flywheel. could be the coil is not advancing. Check, if it has one, the oil sensor by unplugging it. hope this helps.