1981 650 poor excelleration

Not enough to go on, but these were not slow bikes. try plugs, mucky carbs, carb jets, air filter.... take out plugs, any dirty black while others are clean or white? start bike from cold, run very short while and turn off. carefully feel exhaust pipes at top, are thay all same temp? one or two not getting warm? watch you don't burn your hands....will tell you if all cyliders firing ok.