Tomislav Marincic wrote:
> 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
You've talked about every plug except the one I've had the most luck with in my
TR6. For over a year now, I have been using NGK BPR5ES with very good
results. For the first 6 months, I had a conventional points ignition. Now I
am running a Crane XR700 and a new Lucas Sport Coil. Plugs seem to work even
better. I now gap at .034", while I used to gap at .025" with the points.
Remember, too, that cold fouling (black, sooty plugs - not oily) can be the
result of too much ignition retard as opposed to improperly set carbs.
Just my two cents worth...
Martin Libhart
1972 TR6
1970 Spitfire
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