77 Tohatsu water spitting issue

by Jeff
(MO)

I have a 77 Tohatsu 70hp that ran great through all throttle but while trolling would sound alarm after about 25min so checked impeller and it was missing a blade and had been for a long time as it done it a few times before i checked it and it still always ran full thottle good but i changed the impeller and now it cuts water off at 3/4 throttle. The only thing changed is impeller nothing else and it ran fine through entire throttle the day before i changed it. Im stumped. I have checked as much as i can in motor and lower until and flushed motor out thinking it might be missing fin from old impeller but it runs water through it great backwards. Like i said the day before i changed impeller it worked fine with old impeller. They couldnt find my impeller m70a but they said the m70a2 was identicle and when i compared with old impeller it was a match. I cant figure this out bc it only does it at high throttle I can troll ot go up tp 3/4 all day and no issues

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