hi i live in england and have a 305 tpi in a hot rod but has very black exhaust and also smoking (black smoke ) when reving .no fault code .unable to test fuel pressure as the thread on the fuel rail is bigger than the english gauge I have ,could someone tell me the size of the fuel rail thread or have any other ideas

 

go to a plumber shop and buy a few adapters (all diferent sizes and take back the ones that dont work, but i would imagine they are 7/16 or 3/8