My vro on my 1988 xp150 quit pumping fuel, had same symptons like bad primer bulb would not stay hard so I bought a new bulb, same problem so I took the vro back to dealer because I just bought it last year he would not replace it because I put it on, so I took it apart and found the diapham had tear places in it. I took the diapham and showed it to the parts man and he was real nice about it and gave me a new diapham which would cost $35, put it on and motor runs great even idles good which has been a problem. So I thought I would past this on, I havent read anything on this problem before, hope it helps some one. chinist