Stared to do a tuneup and carb rebuild
on my ’78 D-300. While double checking
the timing specs. I remembered that
the engine is a 440-3 out of a motorhome
(stock w/an Edelbrock Performer RPM and
a Weber-built AF) and maybe the wrong
plugs have been in this thing all along
(number 3 plug was miserable to get out).
What I pulled out were Autolite 75 and what
I got sent was RJ18 YC, so should this
rig have a taper-seat plug like a BL9Yor a
gasket seat like the RJ18YC and is the heat
range of the 18s too much?
If it is a true motorhome engine (weird
water pump setup, etc.) then tapered seat.
Otherwise gasketed style. Safest move:
Just look at the hole….if tapered….
Champion heat range 18 is really a hot
plug. The absolute hottest I’d use is 12.
I’d prefer wider heat range plugs such as
Bosch Platinums.