My son bought a low mileage 1987 GL 1200 Interstate. He removed the carburetors and thoroughly cleaned them. He reassembled them and reinstalled them. Bike starts and runs great but has no roll on power above 70 mph. Its like it goes flat. He told me he can apply some choke at speed and that helped but no fix. I originally had thought maybe a problem with slide diaphragms. He inspected those and found no problems. He pulled the spark plugs after a fairly long ride yesterday and plugs looked lean. He also ran a compression test and found all of the cylinders even at 175. Just wanted to see if anyone had any ideas on this. Thank you.