Small Engines (Lawn Mowers, etc.): mountfield mower,, forward gears, fuel flow

Question
Hi
My old mountfield which i bought around 4 weeks ago, ran perfectly for nearly 2 weeks and then refused to start.
Anyone walking past tried to start it over next few days and on day 4 it started for me.
It ran daily for around 3 days then began to splutter and die unless I reduced revs.
It then refused to start. I took off the air filter and there wasn't a filter in there, so I put one in and replaced the plug and the mower started straight away. Unfortunatly after 30 mins it began to backfire very loudly and cut out.
I managed to restart but only for a few seconds.
It is a Mountfield 3 forward gears and reverse with 7hp engine. I belive it is a 25
Many thanks for any advice

Answer
Hi Carol,

The backfiring may be due to a valve that does not have enough clearance and leaks when hot.  Or it might just be a lack of fuel flow.  Try to keep it running by squirting fuel or starting fluid into the carb.

Let me know how you make out.
Michael