Without knowing which engine, one can give all kinds of advice, with most of it being non applicable to your carb.
At least post the Sears 917.xxxxxx number!
Engine brand. model, type/spec are useful, but can usually be derived from the Sears#.
OR, just search a couple pages of this forum!

Sorry, forgot to include the model num:

Sears Hi Torque
6.0 horsepower
#917.372910

I picked this mower up off craigslist.
prior to this issue, _always_ have to prime it to get it to start - even if still warm. any suggestions much appreciated, thanks!

Lex

That has a 143.956000 engine which is a Tecumseh.
My ref doesn't cover that specific model, however-
IF that's the plastic bowl carb, You NEED a new bowl kit....Part # 730235B

If the carburetor has the round bowl on the bottom of the carburetor, til the mower up so the carburetor is on the high side. Then remove the bolt that holds the round bowl on it. try not to let the bowl fall down, although a rolled up rag will keep it relatively in place. Look at the bolt you took out. Look for a teeny hole in the area of the threads, or in the smooth shank of the bolt. Clean this hole with a fine wire, shoot some carb cleaner thru it, then clean out the larger hole in that bolt, and blow thru the bolt. Then reassemble the bowl and bolt, turn the mower wheels down, wait several minutes, then try it. It should start and run!

Thanks for all the assistance!

I should have mentioned that this problem began right after I had turned the mower over to sharpen the blade. thanks to this forum, i was able to locate a user's manual (and Tecumseh engine manual)and where it clearly states not to flip the mower over! (hey I'm a city dweller, what can i tell you :) !

In that case, check the air filter to see if it got saturated with oil.
IF so, you could try starting it with the filter TEMPORARILY removed.

Is the carb a plastic bowl model, or does it have the metal bowl with the brass "nut"?

"Is the carb a plastic bowl model, or does it have the metal bowl with the brass "nut"?"

The bowl is Metal.

The mower now starts up, after cleaning and dissassembling part of the carb and replacing the air filter. I must have done something right :)

It still needs to be primed for _every_ start up, even if its warm and has just been running.

Had the same problem getting started this season with my craftsman 22" 4.75HP mower -- changed oil and air filter, mower would start but immediately die. I took the screw out of the carbuerator and cleaned the three very small holes with water and a rag, blew air through the holes to make sure they were clear. When I put it back together, it fired right up and worked as normal.