Hi,
I have a Briggs & Stratton 16HP tractor mower. Last fall it would only run for 20 minutes with the choke out. I foolishly adjusted the idler screw (or the horizontal screw facing forward) and now it won't start at all. Does anyone know how to tune these carbs?
It's getting a spark and I recon-ed the carb.

No small engine mechanic here but it is my impression that the mixture screw is an idle mixture adjustment only. When you open the throttle the internal mixture jets take over. I would seat or turn the mixture screw all the in and then back it out about 4 turns and try to start. Keep adjusting out 1/4 turns until it starts, then adjust for best idle. If it ran for 20 minutes last fall I'd look for clogged or restricted fuel lines or fuel filters. Also make sure carb is tightly secured to intake manifold. If it has been sitting with gas in it and no gas stableizer used you may have stuck float needle. Tap side of carb, maybe you can free it. Seal tank and blow in it. Air pressure may force needle loose.

Harold,
Thanks so much for the answer. That's great info on the mixture screw setting. Actually I've had this problem since last fall, so I don't think it's the fuel. I checked the float chamber and the needle seems to be nice and free. I'll try your tips tomorrow.
Thanks,
Patrick

I think your problem lies in the fuel system.

I had the same problem as mentioned, after rebuilding the carb.
There is an antibackfire sol. At bottom of carb. That is part of the
Safety device for killing the engine, wired through the seat switches
If this sol. Don't click open when the key is turned on, the engine
Will not stay running

That's some good advice Harold.
But I wouldn't put air pressure in the lines you could mess up the diaphragm in the pump part.you can just take th top of the carb off and clean it out.
Luck