Best plug for a 1955 NH

[CylvaBirch]

I am using a Champion L86C at present and the bike starts and runs well.
Looking at the plug it seems I am running a bit rich but the Amal carb is brand new and jetted correctly according to Waller and the Burlen data sheet.
If I try an L82C she is reluctant to start, so I have stopped even trying to use it.
A series of NGK B6HS plugs sit on my bench in shame, hard to start the bike and a “misfiring feeling” once we get underway. I have now just given up on NGK.
I have ordered a Champion L7 thinking it may be better than the modern “equivalents”.
Does anyone have experience of running L7?
How about a Bosch W7AC?
I have finally found a new old stock Lodge HN in the USA that is ordered off eBay but pretty expensive with postage.
Any feedback would be welcome!
David.

[john.whiting]

Be certain that you are not using a high impedance/ radio supressed plug,or lead,or you will be shortly paying 400 quid for a mag rewind.

[CylvaBirch]

Definately not John. Copper wire, non-resister plug cap and non-resistor plug.
Spark is very good so I am hopeful that the mag is OK.

[robjameson]

I’m using a Bosch w7dc or w9dc, I forget which!

[nevhunter]

Perhaps it is not the plug. The only problem I have ever had with plugs lately is contamination of the insulator inside the combustion chamber, by oil additives. The metal salts ( Zinc and phosphorus), can short the plugs out . Re the Magneto although you have a good spark, it might not be regular. You might have a bit of binding in the points assembly fibre push rod or wear in the diemetal part near the cam. You can remove the whole assembly easily and check. Sometimes the 1/2 length spring is on upside down. The curve should be away from the one with the point on it. Nev

[robjameson]

I had three plug failures in a row while using ngk plugs, couple of broken insulators and a broken electrode. I haven’t had a single plug issue since changing to Bosch

[nevhunter]

Broken bit's like that aren't acceptable. That can damage your motor. I usually use Bosch (or Champion as they still make quite a bigger variety of the rarer types). Today you have to give the vehicle details to get the right plug for the average vehicle. As we know that's not going to get you far with a 1925 model or such, so one has to know a bit about thread size, Reach and hot/cold range and how it's compared maker to maker. I usually buy (say) 10 or so plugs when I subject some older type salesperson to going to the trouble to dig out the required catalogues and spend the time. Nev

[CylvaBirch]

I have taken the plunge and bought a very expensive Lodge HN from a chap in USA plus two Champion L7s and a Bosch plug from the Green Spark plug company, so I now have a full suite to try!
She does start and run well on a Champion L86c rather than a L82c so maybe she likes a slightly hotter plug. Looking at Champions website an L7 is a bit hotter than a L82c but not as hot as a L86c.
Do modern fuels perhaps need a slightly hotter plug?