This goes along with the hard to kick start thread.
So, the thought is that perhaps the coils are not up to snuff. I know the plug needs more juice to spark under compression. The plugs do spark when out. Bike runs fine after startup. But perhaps there is not enough when starting. If the inline led gizmo is lighting does that confirm that the plug is firing?
As I remember, the distance the spark should jump should be 3/8 inch. Is that correct? I realize that this does not confirm that plug will spark in the cylinder. It is just an indication.
I can perform both tests.
Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Hi Bob, I don't know about the actual air gap the spark can jump.
However, On bikes running points, I've seen many Triumph spark plugs out of bike during kicking. The gap is indeed supposed to be .025". Visually the spark looks weak. Not a strong crack like on modern cars or even old cars. Yet the bikes start & run perfectly with this seemingly weak spark. If bike starts & idles, I doubt spark is the root problem.