Spark Plugs

[Pickles]

Can anyone give me advice on what type/ part number of spark plug to use in my 1927 12/4 Heavy?

[Shortstroke]

NGK AB6 or champion D16 are about all you can get nowadays.

[Martin27]

When I took custody of my 20/4 in 2007 it came fitted with a set of NGK AB6. In the box of spares that came with the car was a full box of AB6's. It seemed to run OK initially but after a few miles I was plagued with an intermittent misfire and poor running at idle. I could not find anything wrong but in desperation tried a new set of AB6's. This cured the misfire but about 1000miles later the misfire returned. Another new set of AB6's and the story repeats.

I then fitted a set of Champion D16. 5000miles later the car is running well but the plugs are a bit sooty. D16's are the normally recommended plug and NGK are supposed to be equivalent but my car does not run well on the NGK's. So next I tried Champion D21. I have now run 25000miles on the D21's, the car runs well on these and the plugs stay clean.

I conclude that although D16 is the normal recommendation, the ethanol content of modern fuel results in a lower combustion temperature, therefore needing a "hotter" plug. Of course others may disagree!

PS
I had a conversation with a friend with a Seven who also had problems with sooty plugs and persuaded him to try D21. It cured his sooty plug problem.

Best Regards
Martin

[Pickles]

NGK AB6 or champion D16 are about all you can get nowadays.

Thank you for the information. Much appreciated

[Pickles]

When I took custody of my 20/4 in 2007 it came fitted with a set of NGK AB6. In the box of spares that came with the car was a full box of AB6's. It seemed to run OK initially but after a few miles I was plagued with an intermittent misfire and poor running at idle. I could not find anything wrong but in desperation tried a new set of AB6's. This cured the misfire but about 1000miles later the misfire returned. Another new set of AB6's and the story repeats.

I then fitted a set of Champion D16. 5000miles later the car is running well but the plugs are a bit sooty. D16's are the normally recommended plug and NGK are supposed to be equivalent but my car does not run well on the NGK's. So next I tried Champion D21. I have now run 25000miles on the D21's, the car runs well on these and the plugs stay clean.

I conclude that although D16 is the normal recommendation, the ethanol content of modern fuel results in a lower combustion temperature, therefore needing a "hotter" plug. Of course others may disagree!

PS
I had a conversation with a friend with a Seven who also had problems with sooty plugs and persuaded him to try D21. It cured his sooty plug problem.

Best Regards
Martin

Thank you Martin, information is very useful. I think I'll go with the Champion D21's.