Ohv 400 gardeners choice lawn mower doesn't want to start, got petrol, got oil and the air filter is clean. It's still very new, only used about three times, haven't used it for more than 6 months. Please any tips??

you may have some debris in your gas tank blocking the pickup tube. It will float away when the mower dies, then block the tube after it runs again.

Its to stop the dust blocking the filter. The filter should be cleaned with petrol every 4 to 6 months to remove the dust & oil build up, cleaned in/with petrol and re-oiled. Its also good to clean the filter housing each time you clean the filter

You haven't supplied a lot of information but generally when this happens it is due t the mower being tipped the wrong way.
If you must look under the mower then tip it back with the handles to the ground and front wheel in the air.
Now to rectify your problem; The air-filter will probably be saturated with oil. It will probably be the cartridge type which is not serviceable. Purchase a new filter (take your old filter so the sale person can compare like for like). Before you refit the new filter, take out the sparkplug, it will probably be saturated in oil - wash it in petrol, let it dry then refit it. The engine should start and belch out great quantities of smoke. Don't be alarmed this will burn away. Once the smoke has cleared, check the oil level, fit the air filter and mow your lawn.

Bad gas. Drain gas and refill with fresh gas with Stabil. Old oil. Drain oil fill with fresh 30w oil, 16-18oz. Clean air filter and spark plug.. Relpace air filter if dirty. Saving $$$ on this simple tune up is not intelligent.

adjust the valves, if u have fire and fuel

have you checked the engine oil. most models have an oil motion pick up. they are fitted to most lawn mowers as well when the oil gets week it does not lift and engine will just cut out. replace oil with 20/50 oil.

lol too much oil bud take a little out

if unit is ohv engine - i gather unit is using oil ?

may have a blown head gasket and air filter may be oil / petrol soaked
restrcting air flow

check oil level is correct ( and does not smell of petrol ) wet sumped and breather is working ( not stuck closed )

check for tight valve clearance

if all these are ok then might suspect worn rings / bore ?


may need further info on engine model - type

let me know and i will try help more if can

cheers

remove the sediment bowl located on the lower side of the carburator and dump out sediment then you can check the operation of the float because this is where its located

Check air filter, check screen in bottom of fuel tank,
New spark plug and also check the spark.
If there is a weak spark, the coil may need to be replaced.

If you have good spark, clean air filter, and clean fuel tank screen, then the carberator will need to be pulled of and cleaned out with solvent