I have done the “standard” modification to my Vigor by taking out the end baffles, fitting a 175 main jet and removing the airbox snorkel. All seems well at idle and at speeds over about 35 mph but I’m having problems at slow speeds between (very roughly) about 15mph and 35mph (somewhere around 3000rpm). It feels like fuel starvation – there is a slight “tugging” like the brakes are being lightly tapped on and off. Applying a bit of choke helps this a lot so it seems like the issue is a very lean mixture but only at low speed - possibly an issue with the slow jet. I’ve done several engine chops after a high speed run (i.e. main jet speeds) and they give the right spark plug colour. I have progressively unwound the mixture screw – which seemed to be helping the low speed issue – until the mixture screw came out altogether and is now lost on the road(!). Que Ebay. I’m thinking that the problem might be that, although the increased main jet is coping well, the slow jet is just not big enough to feed the engine with enough fuel with the increased air flow and needs to be replaced with a bigger one. I haven’t seen any mention of upgrading the slow jet in any of the relevant threads on Vigor modifications. Has anyone else had this issue?