by bgsengine » Sat Aug 31, 2019 4:56 pm
One thing - when you had the center plastic main jet piece out, did you also have air cleaner body removed from carb and maybe see if the plastic venturi in carb body might have been loose? Ive had a couple mowers do that - venturi popped loose (it should never come out, its supposed to be very tightly and permanently fitted to carb body, if it's loose it can leak air past venturi) might also want to check intake gaskets (air leaks) - what you describe is what we call a lean surge (which can also be a governor adjustment problem in rare cases) , lean surge is caused by too much air, not enough gas and since you mention it comes and goes, seems to me the problem just might be the venturi portion of the carburetor being loose. (I had one that seemed to fit fine, but fell out when the carb was warm and I popped the main jet out) Also be aware there's an updated version of the main jet - they had problems with the first versions (gumming up) and that issue could not be cleaned since the jet was press fit deep inside the plastic main jet, but it was in a location that was prone to drying out (newer version keeps it immersed in fuel) If your venturi is loose, you need a new carburetor. Otherwise, might be worth trying a new main jet (although there's now cheap china copies of the OE carburetor that are going for less than the dealer cost of the main jet)
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)