I’m gathering this is fitted to a Howard Gem , or possibly one of the larger Cliffords , either way it was by far and away the best engine ever fitted to a Gem.
When you say you’ve had the injector cleaned , was this done professionaly , it needs to be properly overhauled….not just cleaned , my initial conclusion tells me this is your problem.
I’m assuming you are using a starter fuse ??.
Andy.