have you synchronized/Balanced the carbs with a http://www.palmside.co.nz/product_pcid_15854.html
found this worked well for me to get the carbs Balanced also adjusting all idles 2.5 turns out adjusting from here via plug color chart normaly quarter turn or so to correct from rich or lean ( If carbs need cleaning or repair caberator specialist carlton gore rd where fine and ok price well )
A cheap timing light and a degree or two more advance and you should be sweat for under $ 130 if you need plugs and leads not much more new dizzy cap etc .
I can lend you a carb Synchronizer from Mt Wellington and a timing light small deposit