Bob,
RE:"Thanks very much, particularly for the tip on the plugs. It
says to
increase the gap, but doesn't say how much. I have been running NGK BP4HS
at .32 and they keep fowling with black carbon. I figure the mixture is
too rich, but the carbs seem to be set up right according to the Haynes
manual. Are the NGK BP6ES plugs hotter? Will they last longer?"
You are using the wrong plug for a 6-cylinder TR (is that what you
have?)
NGK plugs are numbered just the opposite of Champions. With NGK, a
lower number signifies a higher heat range. TR250's and early TR6's were
equipped new with Champion N12Y plugs. Later TR6's had N9Y, which crosses
to an NGK BP7ES I believe. My car idles rich from ovalled jets, and uses
some oil from worn valve guides, so I use a BP6ES, which is approximately
correct for my car anyway. (TR250) It's a safe choice, since most of my
driving is part-throttle on country roads at 40-50 mph.
Here's a breakdown of NGK's numbering in this case: BP6ES and BP4HS
B=14 mm thread
P=projected type tip (tip protrudes into combustion chamber a bit
more)
6,4=Heat range, numbered from 2 (hot) to 10 (cold). You are running
a very hot plug.
E, H= Plug reach. 6 cylinder TR's need an E, 19mm. Your car has H,
12.7mm, which is probably why the plugs are not getting hot enough
to self-clean. Someone has tried to compensate by using a much hotter plug.
I'm surprised the car runs at all.
S=standard 2.6mm center electrode.
You didn't mention what year car you had, but try starting with a
BP7ES. If it runs well and the plugs don't foul, you're all set. If your
plugs foul, try BP6ES, particularly if most of your driving is around town.
If they don't foul with BP7ES, but you do a lot of aggressive high-speed
driving, consider BP8ES as a precaution. BP4ES is way too hot, and BP4HS is
both hot and incorrect.
Good Luck,
Tom Marincic
CD3574L
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