I have an 8E Villiers engine I’m looking to use and wondered if anyone could give me some advice on primary gearing. I notice that Villiers Services do 15/16/17/18 primary sprockets. Any views on what would be best? I have the 4 speed box and again wondered is there is much value in extra low 2nd and 3rd gears?
 

any advice appreciated

If you go too low on the primary, clutch slip could be a problem. It also makes the bike harder to start. I prefer to go as low as possible on the gearbox sprcket

Teamferret. Yes that's a good point.I had that problem on my Cub when I dropped the size of the primary sprocket. I guess it's probably best to stay conservative on the primary sprocket and experiment with the final drive ratios then