I have a 1999 ACE 750 that I have ridden and maintained for 15 years. It has 47,000 miles on it. I did all the upgrades that I learned from this site over the years. I am completely stumped about the latest problem that I have. The bike starts fine (after I just replaced the started switch assembly) and all is okay at idle. Twisting the throttle to raise the revs while in neutral seems fine. Once I get on the bike and attempt to go for a ride, it doesn't like to accelerate, to the extent that I can't get over 50 mph, even with full throttle for a mile or so. This is an issue that happened after I had ridden 10 miles without issue and parked in my parent's driveway for an hour or so. When I went to leave there, I immediately found out that acceleration was an issue. I took the bike apart and can't find any cracked hoses. The four plugs seem to have proper spark. I can't find a way to recreate the problem at a standstill. The battery is quite new. The plugs have normal coloring. Neither cylinder has an obvious issue. This problem is consistent under load. I can't figure out what direction to go in for the next step to diagnose the problem. My dad has the exact same bike and he is also out of ideas. Any direction or suggestion would be vastly appreciated.