Plug Fouling

[Mosin]

Can I pick your brains guys?

My A7ss is running lovely (except perhaps for a little difficulty starting). But I am finding that the right hand side plug is sooting up to the point where the engine runs very lumpy and then drops to one cylinder after about twenty miles. If I take the plug out and clean it, off we go again. The left hand plug is consistantly in perfect condition.

So far, I have checked the points, plug gaps, replaced the complete HT leads on both sides including the plug caps and pick-ups and cleaned the inside ring of the magneto using a stick with a bit of rag soaked in petrol as described in Haynes. None of these seem to have made any difference.

Can anyone suggest anything else to try?

Thanks,

Simon

[beezalex]

How far up the insulator does the mixture ring go on the left (good) plug?  It IS fuel fouling you're seeing, right?  Sooty, not oily?

There has been some discussion about bias spacers on this forum, but the more likely culprit is the ignition bias suffered by an inconsistent point gap.  This has also been discussed at length.

[bsa-bill]

What plug are you using, maybe a hotter plug would cure it.

All the best - Bill

[Mosin]

I am using NGK B7ES plugs on both sides.

I have just double checked the points and discovered that whilst the gap on one side is dead on at 12 thou, on the other side it is quite a bit wider. Does this sound like the cause of my sooting? If so, how do I go about changing the one side without adversely affecting the side that it set correctly?

Apologies for my unacceptable ignorance of what should really be the most rudimentary piece of schoolboy mechanics.

Simon

[BSA_54A10]

Widening the gap will retard the ignition as it will take slightly longer for sufficient potential to build up to force a spark to jump the gap.
This will do either one of 2 things.
1) cause the spark to track down the side of a slightly contaminated insulator = miss.

or

2) cause a fouled plug to fire and eventually run clean.

Which way it goes in any particular cylinder seems to rely on Vodoo more than any combustion or engineering principles.

The only way to get plugs exactly the same is to use one of those plug testing machines which tests your plug under pressure but they are very hard to find now days as the plug companies stopped making them as they reduced new plug sales.

[a10 gf]

one side is dead on at 12 thou, on the other side it is quite a bit wider

magneto points cam & timing, see http://www.a7a10.net/forum/index.php?topic=1375 & http://www.a7a10.net/forum/index.php?topic=1610.0

A little l\r difference in points opening gap should not affect spark strength in any big way, but timing may be off.  Seems like your mag may need a tune-up, whatever the cause of the R cyl sooting.

[dpaddock]

Actually, closing the points gap will retard the timing; one flat equals 2 degrees.

David

[Mosin]

Well today things have just gone from bad to worse. Or at least, to more confusing...

Last night I had a right good tinker with the points and got the gap on both sides as close as I possibly could. This morning she started second kick and after a few moments just running on one cylinder settled down nicely on two. I went for a ten mile run, stopping half way to fill up with petrol, after which she started first kick. All seemed well and she was actually running really nicely. I got home and figured I'd have a quick look to see if the r/h plug was sooty. It wasn't. 'Great' I thought, all sorted!

But alas no, When I tried the bike again a couple of hours later (after touching nothing else in the mean time) she fired just on the l/h cylinder. I set off, thinking that the r/h would kick in as thing warmed through. After a couple of hundred yards it was clear that this wasn't going to happen and I limped back home running just on the left hand side.

Much more tinkering with the plugs, points HT pickups etc and now I cannot get the bike to run at all. Grrr.

But the really weid thing is that I tried using an ignition tester on the r/h side and it is showing a very good spark between the ht lead and the plug, but this just doesn't seem to be igniting anything in the barrel. And equally crazily, my tester isn't showing me as having any spark at all on the l/h side regardless of what I do.

To say I am confused is an understatement.

[bsa-bill]

I think my next move would be to replace plug leads and caps

All the best - Bill

[Mosin]

I think my next move would be to replace plug leads and caps

All the best - Bill

I replaced them with brand new ones a couple of days ago. I also tested them for resistance at the same time and they showed up as having virtually none.

[A10Boy]

In circumstances like this its time to go back to basics. Check and reset everything from scratch. Clean the mag ring, pick ups, refit the ht leads, new caps. new plugs, clean the points with a mag file and reset the gaps. If you do all that and still no spark, the mag must be duff. Its not something silly like a bad cut out button is it?

[bsa-bill]

I replaced them with brand new ones a couple of days ago. I also tested them for resistance at the same time and they showed up as having virtually none.
[/quote]

Was this after or before your troubles

All the best - Bill

[Mosin]

I replaced them with brand new ones a couple of days ago. I also tested them for resistance at the same time and they showed up as having virtually none.

Was this after or before your troubles

All the best - Bill
[/quote]


I've had it running well since replacing them.

[trevinoz]

I would not use NGK plugs in any British bike. I have tried them and had nothing but trouble.
I stick to Champion.
Trev.

[BSA_54A10]

Plug leads must either be solid copper, or spiral wound inductive type.

Normal car leads ( graphite powder in a fiberglass matrix ) will not work.
Even worse is that they will test ok and may even throw good sparks the when you get underway and vibrations start the graphite powder will shake away from the high points and the lead will go open circuit.
This applies to any and all graphite leads which includes Harley , BMW's or any other motorcycle branded leads.