Thanks everyone for the replies, I've ordered a new plug cap, ignition battery with heavy duty leads and a new plug, I've taken off the cowl and I'm going to clean the carb, hopefully that will make some difference!
The reason I ran the engine at the field with the cowl on was because of the CG issue so I'm going to re balance with it off to make sure

I'll try and get it going in the next few days!

Thanks