Norton 850 spark plugs

Used Champion N7Ys in all my Commandos since 1977, 750s and 850s, that includes the racers, never had one fail- what's the problem? Rode on my Commando fitted with 2 N7Ys to work this morning. Andover Norton Part# 06-2348..........

If your engine is unmodified and in tune the recommended plugs should perform perfectly for many many miles.We need more info in order to help you get to the bottom of this.Are you experiencing starting problems, or running problems? Are the plugs becoming damaged (ie. melted electrodes, or cracked insulators.), or fouled (ie. electrodes gummed up with oily deposits)?

Have you tried cleaning the plugs which supposedly have gone bad by sand or bead blasting? If they work after being blasted it is obviously a fouling problem, and you should look elsewhere for the cause, like the carbs.

Plugs break down in only a few ways: The electrodes can wear/erode until the gap is too big for the spark to jump, but that's an easy fault to see and check for. Or, the HT current can find a way across to the other electrode without jumping the gap. For this to happen the ceramic insulation can become cracked, or deposits on the insulation can become conductive. Blast cleaning can remove these deposits, butI'm very wary of sand/bead blasting plugs because of the danger of residual sand dropping into the combustion chamber and scoring the barrels and pistons. However, you really shouldn't need to clean the plugs if the engine is in good mechanical order and in tune. Factors that I would like to eliminate are: How fresh is your fuel? (Modern unleaded petrol seems to go stale quickly.) What's the compression like? Is the charging system maintaining full voltage, and is the ignition system receiving full voltage?Are you on points or electronic ignition?

If the motor is using a little oil try one grade hotter plugs. Champion NY8 or NGK 6, don't use plugs marked with an R with suppressor caps. Retarded ignition can cool the plugs preventing them from self cleaning.

Try NGK iridiums, details found on the NGK website. These are fit and forget if you carb set up is good. Some have a few problems, but this may due to to high a resistive cap, and / or poor connections in the ignition circuit.

Sounds like your pilot jet system is too rich or you have excess oil from a mechanical problem, valve guide, seal etc etc. Lean off your pilot system to see if your bike still starts, ticks over and the plugs stay tan coloured.

Sounds like an ignition problem to me with the plug working when you increase the distance from plug to cap. Does it happen on the same side every time? replace the plug leads with copper items and a cap with no supressor. Are you running an electronic ignition? try a 0.030" gap. Convert back to contact breakers to see if the problem continues. Swap the coils from left to right and see if the fault follows. Borrow a set of known working coils from someone in your nearest branch. Good luck, let us all know how you get on.