Mowing and running fine. just died.now wont start. sounds like puff puff puff when trying to start.also what is spark plug gap setting for 24hp intek twin v ohv

burned valves

do a compression test, see 100PSI expect
choke off throttle open.
spark plugs all out.
bad engine i think with backfire,
on a car, cam belt bad
but this is gear drive. so bad valves

Exhaust clog, stale gas, clogged fuel filter.

sounds like you may have a bad coil. you getting gas but no spark if its sputtering can cutting out or it may just need re gapped

timing key under flywheel costs 1 dollar

check compression and spark if both are good rebuild carb

see if it loosing spark when this happens the coil might be cutting out

A common loss of power problem with B&S V twins is a set of crumpled valve push rods. Means you are running on one cylinder which is generally OK unless you also want to mow. Easy to check, pull one plug wire at a time off. If it continues to run on one cylinder but not the other, that is your dead cylinder. As the intake is not opening, there will not be a wet plug. Costs nothing to check and could be your problem.

This same thing happens to me and I resolve it by taking the gas line off in front of the carb and blowing air through it.....then it will run fine. I realized I could do this when I took the air cleaner off and fed it gas manually and it ran fine....and I also had gas pumping through the fuel pump. I'm not sure of the problem....either the fuel pump is losing power or their is something blocking the carburator intermitantly

sounds like a timing issue

you need spark, gas and timing to make it run. have you checked spark? sounds like you are getting gas. did you hit anything hard with the blade while mowing? this can throw it out of time.