Lagging at top end speed

[Nick simmons]

Hello, requiring a little help please. Completely restored my little CB77 which has been as good as gold, really good fun to ride. I have been getting a top speed of about 90/95 mph but recently it’s not been going much faster than 70/75 & feels like it’s holding back slightly when flat out. It gets up too speed perfectly well but just lagging a bit on top end. I haven’t changed anything. Any help as to why I have lost 15/20 mph would be greatly appreciated. Thank you!!

[Merz64cb77]

Have you taken a look at the plugs? What do they look like. Also what does your oil look like and did you rebuild the carbs? I would also check the petcock bowl and see if all is well. Are you using the original gas cap? I’m just wondering if it’s venting