I had a situation similar to this. I put a carb that needed a choke cable onto a 6.5 hp Briggs. I changed the backside of the air filter box to one that has the primer built into it. Seems like it helped it start. Or am I hallucinating? Is the internal venting and such on a choke style carb such that a primer would work on it. I know have not included any model or part numbers but I sold the mower after replacing the air box and do not have access to any model number detail. Just asking a general question. Thanks