Ok well I finished my road bike project, my enduro project and its time to get back to the trail boss. Its a 87 250 4X4.
So autozone told me the spark plug was a br8es. But bikebandit.com shows the oem spark plug as a RN4YC, a champion plug.
So just to be sure I figure(because autozone has given me incorrect parts more often than not) and i checked a spark plug cross reference chart.


For anyone looking for it here is the link for the cross reference chart i used
SPARK PLUG CROSS REFERENCE


At any rate the RN4YC cross references to NGK's BPR8ES, not the BR8ES.
And from what i have found out the "P" means that the electrode protrudes more than the non-P. Maybe this is why it doesnt run right.


So my question is this, lets ask the experts(you guys), what plug do I use????

 

Shows 89 models and up 250 engines called for BR8ES, 85-88 models show BPR8ES. Just check the head and make sure BP plug doesn't extend too far! I started in 1988,can't really remember earlier than that,just going by the old Polaris Parts break down. I almost bought a 2000 explorer 250 that was a real cheap trade in, like new shape,wish I had! OPT