the way i found out i was having this problem is my motor would not stay running, i'd pour a little fuel down the carb and she would fire and then a few seconds later, my engine would stall, at 1st i thought it was the fuel pump but when i dropped the fuel pump, the pushrod wouldnt come out. after finally removing it, it lost a good 1/4" and it was totally mushroomed, i saved it for years over my kitchen sink, i just threw it out a few months ago.
i think i put another MP one in, i havent had a problem yet but i think i need to inspect it again.