I restored a 1983 Searay Seville 4cyl 120hp completely. I put new gimbal bearing when overhauling bellhousing. Prop is locked in forward, splines line
There were 2 pumps installed on these 3 cylinder motors !!!!!------------Need to run with a timing light to see if it is ignition related.---------Could
The o-ring should be enough.
Just make sure it's CLEAN, CLEAN, CLEAN.
A bit of grease to hold it in place will help.
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You will be fine with the OMS pump. The newer pump mixes at about 60:1 at WOT and close to 100:1 at idle.