Awhile ago I installed a 13.13 Dellorto carb and a techno circuit pipe on my otherwise stock 90s ciao. It's taken me awhile to get a good seal on the exhaust and to figure out the right jetting but I finally got it to a point where it seemed be riding well but then it started to ride somewhat irregularly. It'll start up well, takes a minute to warm up and then gets up to speed gradually. It was getting good speed at wot. After riding it for awhile though (maybe 10-20 minutes) it loses power and dies, both gradually and sometimes immediately. Also the top speed I can get out of it varies quite a bit. I have a 55 main jet in the carb and I just put new gas and a new sparkplug in. I was also running it at night with the light on if that makes any difference.
Can anyone tell me what's going on here? Is this a symptom of running rich or lean? Obviously something is changing once the engine heats up.