32/36 weber on a 1600 xflow running rough

Guys I have a 1600 in my khanacross bunky it's not standard but what cam it has I don't know? It's got a electronic ignition and a 32/36 weber off a pinto and it runs fine in 1st,idles fine revs fine but when changing up a gear it coughs and farts and goes nowhere it feels like i have changed from 1st to 5th

Anyone got a idea what's going on??