Yes, safe. To be super safe, take an old oring made of rubber, even a rubber band, drop it in the shot glass, come back in a day. Swells... nix the fix. What is left is to send them out to a place that cleans and tests injectors, or buy new w/orings and all is peace of mind.
It's all about a clean hole. 3 circuits on a carb and once vacuum begins pulling, it pulls from all 3 equally. Clog one its hard staring, long starting before firing, lost pep, better gas mileage. So back to a simple diagnosis... Touch the starter button. Did it fire right off and purrs at idle? Then there is no injector hole needing to be physically open with a needle point/etc.