Thanks for the idea�s Theo.
The mower is now running like a charm.
The problem ended up being a piece of foam pre-filter stuck in the air intake which was inturn restricting the amount of air the engine could suck in through the air filter. I didn�t see it initially. I just took the old air filter out and gave it a blast with the compressor to get rid of all the debris inside. Only when I looked down the snorkel with a torch did I see the foam pre-filter broken into a couple of pieces and just about covering 80% of the air intake (hence why it was running so rich).
With my multipurpose crochet hook this piece of foam was easily removed. The mower fired right up and just about smoked out the paddock I was testing in however after about 2-3 minutes it cleared right up and continued to run perfectly.
For my own curiosity and installed the original muffler and the engine wouldn�t start (thus confirming the blocked muffler)
So I am assuming the previous owner continued to mow with the air intake badly blocked which caused the engine to run rich until it blocked the exhaust completely and wouldn�t start. So all the [Censored] thing really needed was a new exhaust and that stupid piece of foam unjammed from the air intake!
Lesson learnt�.. always check the [Censored] air intake with a torch and don�t just blast the compressor down it.
Hope this is of use to some others!
