venting the cap would not cause this. this is a sepperate issue happening at the same time (Mr Murphys handiwork) unless we are missing something in the repairs that has tied these 2 issues together. loosen the cap or remove it & take it out for a drive like before & see what happens. if it is real dusty you could duct tape a piece of porous cloth over the neck but unless it is a dust storm (just me) I would not sweat that. Then if it (still) acts up, plumb a gas can to pump inlet. Correct, a pushrod issue would not be intermittent. that is strange symptoms tho, that it wont pick it back up even after priming the carb (& thats priming the carb more than once I assume). I feel like it is just with reach but I cannot grasp it (but we will). EDIT even with the notches added I think the cap ain't venting. my other choice is bad pump, other possibilities are a clogged sock