just curious what spark plugs i should be running in stock 502 jasper motor in my Baja? right now i have NGK R (BR6FS) plugs. Had dads friend who is mechanically inclined that he doesn't think they are right, it thinks i should be running NGKUR4? any input on what i should be using?

What is a jasper motor? First time i hear that

jasper motor is just remanufactured 502. Think their built more durable

Definitely not more durable than OEM Merc. Jasper are ok, but their marine engines have a much higher failure rate than Merc.
The BR6FS are the correct spark plugs for a Merc 502.
I assume your Dad's "mechanically inclined" friend doesn't work on marine engines.
UR4 plugs are too hot and could cause detonation. You could run a UR6 which is the same heat range as the BR6FS with a projected tip

what about the AC DELFCO RAPID #1? Can you use those?

Griff,

Any specific known reasons for the higher failure rate? I've always heard good things about Jasper engines, so I figure it's a marine thing. Bearing clearances? Valvetrain? Curious.

Thanks. Brad.

in the automotive industry, Jasper does not have a good reputation, I would guess the same applies for marine

BR6FS Cross’s to delco mr43t which is correct plug for merc 502/rectvport cast iton head motors. Gap to .035”.

i run NGK ur5 they work awesome

I’m a V Power junkie also.