Spark Plug question for a 1954 Tea 20

Having read the importance of fitting the correct plugs on these old tractors I finally decided to see what plugs my tractor had.
I rebuilt my engine last year and it runs very well. I use it to mainly Slash/Brush Hog and at times I tow a trailer aroung the property.
I did not change my plugs after the rebuild as on the outside they looked as if they were new.
I note Champion L10 was the original (Now L86C) and the equivalent in Bosch is W7A and B6HS in NGK.
I removed my plugs to find NGK B4ES and went to the local spare parts outlet to buy the correct plug.
Champion was not available so I settled for NGK B6HS.
At home I noticed that NGK B6HS is a short threaded (13mm?) plug and that NGK B4ES has the much longer thread.
I fitted the new plugs and cut the grass for 2+ hours and felt no difference but noted at low rpm's the engine was missing. I tried adjusting the mixture to no avail.
Next day I attached my trailer and still noticed that it was missing at lower rpm's.
I then removed the new plugs and refitted the old and then adjusted the mixture and all was back to normal.
I do recall reading that some think that the longer threaded plugs are better for these tractors.
Anyone have any views on this subject?
Regards Brad

the lesson i heard is leave well enough alone!

BH6S is the correct equivalent. A miss is not necessarily the plugs or fuel.Check the points for instance. mine are known to change often.Matter of fact it was missing yesterday, due to low fuel in tank..Must be some bogeys in there somewhere.
Fortunate there is sufficient room in chamber to take the longer plugs.

Hello, the TEA20 had a 1/2 inch reach threaded plug, the TED20 vaporising oil tractor used a 3/4 inch reach thread sparkplug and they had the full 3/4 inch tapped in the cylinder head. Measure the thread depth, it should be 1/2 inch if the tractor has the correct cylinder head so the B6HS will be correct. In Australia most of us use a BP6HS, the only difference is that the electrode protrudes a little further from the end of the sparkplug to ignite the fuel air mixture better, the only downside is that if the engine is burning oil they will fowl up, hope this helps.

I won't say this too loud but in Australia Champion spark plugs are not the best solution! I find NGK a more reliable solution...........

TEA's only have short reach plugs, only kerosene engines need long reach type. The plug you used should be fine if it is set to .030", make sure that the points are also set correctly i.e. .012" for a 6 volts and .015" for a 12 volt. Are you sure that you are adjusting the carburettor correctly as there are 3 different types of main jet on these Zenith Carbs and one of them is more or less open and shut when you alter the adjuster and if you have one of this type then it could be your problem more so if you did not set the Carb when the Engine was hot, not just warm.
John(UK)[email protected]