1966 BSA A65 Lightning Spark Plugs

[A65rider]

I have been running the above bike for just over one year. I have a recurring problem with the LH spark plug that I wondered if anyone could offer any thoughts / help with.

Shortly after purchasing the bike I did a minor service, ie oils, plugs, filters etc and replaced the existing NGK plugs with similar grade NGK B8ES.

After some 573 miles I experienced the engine not firing on the left hand cylinder. Luckily I’d kept the old plugs and by substitution came to the conclusion that the plug had failed. I also noticed that the plugs I had originally removed from the bike consisted of a B8ES and a B7ES (not sure which went in which cylinder but think the 8ES was in the right).

I discussed this with a technical bod at NGK UK and his advice was to stick with the cooler 8ES plugs. However I upgraded to Iridium plugs (NGK BR8EIX) as I thought these might help with the general starting problems I was having and have a longer life.

After a further 726 miles the BR8EIX plug failed and I replaced it with another same spec plug. This plug has now failed after 340 miles. Note after about 200 miles I took the bike to a professional establishment to have the timing checked dynamically and the carbs tuned by someone with more experience than me (not difficult). The timing was measured at 35 BTDC and reduced to 32 BTDC. The bike was running ok before and after the tuning albeit that it ticked over better afterwards.

Having looked again in the BSA workshop manual they recommend Champion N4 plugs which I think is equivalent to a NGK B7ES (some debate here as I’ve heard there is some overlap and its more like a B7.5ES).

Any views on what the cause of the problem maybe, should I move to 7ES plugs or even go back to one 7 and one 8.

[chaterlea25]

Hi,
There's probably a reason(s) why the plugs have failed  failed plug is a symptom not a cause (usually) 
Are the failed plugs black and sooty or oily? or burnt and grey looking?
What ignition system has the bike fitted? original points and coils or electronic?
Are the carburetteurs in good condition and synchronised properly?
Is the engine in good mechanical condition and is compression more or less equal on both cylinders?

Where are you based? Try and find a well recommended classic repair shop or fellow A65 owner in your area

HTH
John

[R]

Agree with John, its likely a bit of oil burning or a worn carb or low compression  is the prime cause here, and plugs are only the result.
You might get away with running a grade warmer plug to 'fix' this...

[A65rider]

Gents, thanks for your responses.

The plugs when failed tend to be black and oily / sooty.
The bike has a new pazon ignition system with dual coil.
The carbs are new and they are Amal 930 Concentric. They're as synchronised as I can achieve in terms of throttle opening, tickoever and pilot air.
The bike runs well normally, I have observed different compression at around 130psi with the RH being lower than the LH. Just lately however I have got some low readings (90 - 100 psi) again with the LH being higher than the RH.
I've just given the cylinders an internal examination through the plug hole to primarily look for oil pooling in the valve cut outs on top of the pistons. The piston tops were patchy clean metal / black with flaky carbon on them (I decoked 1500miles ago), there were no pools of oil but the bores looked a black aswell not the smooth polished look I remember. This however may be a reflection from the piston top.
I've also learnt that with electronic ignition and a dual coil one plugs fires normally and the other from the outer to the inner. This does shorten plug life but not to the extent I'm seeing.
I intend to swop over to two 6v coils in the near future but I'm not sure that this is the complete answer. I guess I need to get the head and barrel off and look at the valves and rings this winter.
I've just put in some Champion N4C plugs which are hotter than 8ES so I'll see how they go although I wont be doing much mileage in the next few months.
I'm based in Suffolk, just down the road from Andy Tiernan but they don't operate a  workshop as such and the nearest BSA OC is Norwich.

[murdo]

I've never had much success with NGK plugs in English cars, always found Champion Gold (made in Mexico would you believe) give good life, and use the N2c series in my German bikes (made in Belgium or France).

[chaterlea25]

Hi
Use the camera to have a look into the ports,  look for oil coming into the ports down the guides
Have you checked the valve clearances since the decoke?
Compression is low??? are you opening the throttles fully when testing?
Swop over the plug leads from the twin coil and see if the problem moves to the other side
I would also check the fuel heights on the carbs,high fuel level on the problem side may make it run rich
Its well worthwhile to hook up vacuum gauges or a "twinmax"  to synch the carbs
Remove the balance tube and attach gauges there


HTH
John

[P.V. Motorcycles]

I doubt it's the plugs - nothing really 'eats' plugs these days.

I'd suggest a post on the 'britbike.com' forum. I look in on the Triumph one, and at any given time there's a post up about whichever brand of electronic ignition a forum member has installed. Some are very sensitive to the battery voltage, some require different coils, some show up bad earths and connections in the loom etc. Some are simply installed incorrectly.

That's not to say any of them are bad products - they're just possibly not as forgiving of less-than-optimum conditions as the old Lucas points system was.

Nick

[P.V. Motorcycles]

As in the post above, a common recommendation on the britbike forum when folks are complaining of ignition problems on one cylinder only is to swap over coils, leads and the like (but not the plugs!) between cylinders. If the problem swaps sides, then you know where to look to address it.