I have a yardmachine with a B & S 17.5 engine. Replaced with short block. Now will not start. Seems to not want to fire. Has fire and fuel. Is it possible for the timing to be off?

Was it done by a shop.
And was it a true short block.

I did it and it was a purchased short block. I adjusted the valves at TDC.

Onthis model you have to go a 1/4 inch past TDC to set the valve clearance

I am confident valves are adjusted as you mentioned. While starting engine, it sounds like it wants to start but not quite. Backfires and a lot of gas coming through carb and flooding at the cylinder.
By the way, thank you for your help. I feel I am much closer to getting this thing running.

If it spitting out the carb this sounds like the exhaust valves isn't opening enough.
If you bought a short block from the factory the timing should have been set.
If the fly wheel isn't seated good the key could have sheared this would make it out of time
Did you set the armature /coil at .010 or a business card.