Hi I see the high speed adjustment is the screw that holds the bowl
How can I identify the low idle screw?

Usually its up top, there should be only two more, one that just acts as a stop for the carb's butterfly on some.. The screw at the bottom doesn't hold the bowl on though, its screwed into a fuel bowl nut, the nut holds the bowl on.

I just started an generator it has a 4 cylr engine on it and I noticed it is running rough and escessive backfire any idea where to start and what can cause this plug was changed the last time it was used about 6mos ago
stablizer in in the fuel

any ideas?

Doesn't sound like the adjustments then, Even though stabilizer was used, could have trash or water in the carb (water will get in from condensation from the gas tank not being full to minimize it)

Hi thanks will look the fuel situation will dry gas help out?

With water, it will... the rest it won't.

So it would be best to run it out or dump it and start fresh?

Dump it and start fresh, if the gas is old and has no water in it..... then just dump it in a relatively full tank of gas in your car.... same for 2 cycle gas/oil mix.... won't hurt a thing.

I have seen some carbs on older Briggs engines with the high speed adjustment screw going straight thru the center of the bottom float bowl attaching bolt. These carbs have the low speed mixture adjustment as a flat head screw on the top and one small screw as the idle speed adjustment.