So…What are your views on sparkplugs?I have used ngk 18mm which run well, but it is difficult to start.I have also tried some old 18mm ,make not known,that start the engine well but it doesn’t run as smoothly at speed.I was once told that 18mm plug were better in a vintage two stroke as the bigger diameter made the plug less likely to foul!! Fact or fiction?Your views gratefully received. 😀
If your bike is made for 18mm spark plugs, you should use those. 5-series NGK plugs are usually ideal for Scotts. Plug gap should not be excessive – ca. 0.020″ – 0.022″ (0.5 – 0.55mm) is suitable for magneto ignition. It is difficult to get 5-series in 18mm thread. The closest will be A6 or AB6 (6-series). Champion D16 can also be used, as well as Bosch M8AC0.
You may use 14mm plugs, but then you must use inserts to reduce the thread diameter in the plug hole.
I would then suggest using the NGK BKR5EIX – an iridium 14mm long reach plug. I use this on my 1936 model, and for the first time, no misfiring or other plug problems. This type of plug is a bit expensive, and a cheaper variety, NGK BP 5 E or B5ES can also be used.
So-called “Radio plugs” with internal resistors should be avoided in bikes with magneto ignition. Sparks are not as “fat” as withncoil ignition.
Just a note that for most plug manufacturers, and I’m sure for all NGK, if it has an “R” in the part list it has an internal resistor.
I use both 18mm and 14mm plugs and to be honest I’ve not really found much difference provided the ign is in good condition, plugs are clean and something around the right heat rating is used. A slight preference for 14mm just because they are easier to obtain locally.
ive been told that the best plugs for scotts are lodge c3 but i would have thought that cb3 would have been better they have a bit longer reach. i think the original plugs were champion 7.its nice to see you guys passing your knowledge on
I have used iridium plugs and think they are really good in my DPY motor. If I were in your shoes I would make absolutely sure the mag, pickups, ht leads and plug caps are 100% good.
Does anybody have a source for the plug adaptors and plugs please?
I regret that I cannot help you with plug adaptors, But like Rich, I would especially mention plug caps. Modern plug caps more often than not have resistors built into them, and are not suitable for magneto ignition. Modern plug cables may also have a high resistance. I will again especially also stress the importance of correct plug electrode gap
(ca. 0.020″ – 0.022″ (0.5 – 0.55mm). When you buy new plugs they will have a much larger gap (ca. 0.8 – 1 mm). Lodge CB-3 plugs ore its equivalent Champion 7-Com-L are regrettably no longer available.
I have used loge C3 champion com 8 and Bosh 240 T1 over many years gap 18 thou. all perform well at normal road speed.
Thanks for all of the replies, i may try to get a nos lodge or similar.I have never had much luck with any of my vintage bikes when using the modern ngk or equivalent plugs.I am fairly confident about the ignition as when the bike is warm it will start first kick even with the ignition fully retarded and it will tick over like a stationary engine . 😕
I get mine from there, not worth making them myself for that price! Remeber to buy the washers too.
The problem with NOS is it is several decades old and you don’t know the storage and transport they get subjected to. Given they have been through factory closures, auctions, autojumbles et al NOS plugs are usually not a safe option from my past luck with them.
Interesting thread though.
well good news.I seem to have sorted the starting and running problems.First of all i found a tiny air leak on the lower edge of the inlet manifold just above the flywheel where the sealing surface looks very narrow.The 2nd fault was that when checking the points gap i noticed that there was quite a large variation of gap at the two points of opening which was causing the high speed missfire.On checking there was run out on the end of the shaft which was causing the uneven opening.A call to dave lindsley confirmed that in his experience that this was a common problem with the bth mag.The fix was to remove the outer cover of the mag and shim the top mating surface with a piece of the brass shim plate.I know it may not find approval from the engineers but it seems to of done the trick and it remains to be seen if there is a long term penalty to pay for doing this.Anyway,for once,at this moment in time,everything is good in my scotting world. 😆