Hayter Harrier 48 - (B&S) wont start

Hello all.


I was wondering if you could help me out with an issue (probably self-made) I have with lawnmower.
I recently run into some problems with my lawnmower (7 years old Hayter Harrier 48 with Briggs and Stratton Engine) and ended up with a broken “carrier blade boss”.
I consider myself to be ok at DIY and as such and whilst getting a replacement for a broken "carrier blade boss" this I decided to service my engine, so I ordered a service kit and went on to do the work.
So work I completed,

• - Replaced air filter
• - Changed spark plug
• - Checked carburettor (spotless)
• - Replaced carrier boss and generally tidied engine.
• - Sharpened and balanced blade – put some hammerite paint on to help stop rust.
• - Removed carbon build up on piston heads and valve heads (was careful around valve heads and seals).
• - Replaced gaskets on both crankshaft and piston head being careful not to damage the aluminium (used a plastic paint scraper)

Problem is I can’t get it to start at all. I checked spark plug, fires ok. I put some petrol in spark plug hole and got it to fire once. I checked carburretor and all looks like new.

I was wondering if you would be able to help me get it back running and undo and problem I may have created.

thanks in advance.