BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: D COLTMAN on 18 February, 2017, 14:23:28

Title: spark plugs
Post by: D COLTMAN on 18 February, 2017, 14:23:28
hi all, I have a 52 star twin that keeps burning out plugs, I have used B7HS NGK and champion L82C , has anyone had the same problem?i have done 150 miles since complete rebuild but never had this problem when I last had it on the road approx. 25 years ago!
Title: Re: spark plugs
Post by: STAR TWIN on 18 February, 2017, 14:58:46
Something odd going on if plugs are actually burning out. Are the electrodes melting? My '51 Star Twin has run happily for many years on NGK B7HS plugs and bog standard carb settings.
You do have to be careful to avoid counterfeit plugs - if they are too cheap to be true, they are indeed too cheap to be true.
What colour are your plugs? White means running too weak.
Title: Re: spark plugs
Post by: Arthur on 18 February, 2017, 15:05:24
hi all, I have a 52 star twin that keeps burning out plugs, I have used B7HS NGK and champion L82C , has anyone had the same problem?i have done 150 miles since complete rebuild but never had this problem when I last had it on the road approx. 25 years ago!
This means different things to different people. When you say 'burning out' do you simply mean the plugs have stopped working electrically or do you literally mean the electrodes are burning away?
Title: Re: spark plugs
Post by: D COLTMAN on 18 February, 2017, 16:45:07
hi, the plugs just stop working ,running ok but running the engine in so not opening up too much
Title: Re: spark plugs
Post by: Arthur on 18 February, 2017, 17:01:06
When you say they have stopped working, have you put an ohm meter between the central electrode and the cap and found they have gone open circuit? However, this would be very unusual for a modern spark plug unless the engine has been running very hot!

Or is it just the case that the engine only runs well when you put new replacement plugs in? If so, it's likely that either the engine carburation is not right or the engine has a different issue (eg poor compression or incorrect valve timing).
Title: Re: spark plugs
Post by: STAR TWIN on 18 February, 2017, 17:58:46
If the plugs are black, they will be tracking to earth rather than sparking. It also implies running too rich - choke kept shut?
Title: Re: spark plugs
Post by: ANDY HIGHAM on 18 February, 2017, 21:31:57
My guess is they are fouled
Title: Re: spark plugs
Post by: D COLTMAN on 19 February, 2017, 18:51:23
thanks for your replies,done about 15 miles today and everthing ok, plugs light brown in colour in the middle but black on the outer, opened it up more today as still running in , never missed a beat. how do you check plugs with an ohm meter?
Title: Re: spark plugs
Post by: Arthur on 19 February, 2017, 19:34:39
It sounds as though it's running fine. I don't think there's anything wrong with your plugs but, if one had failed electrically the copper wire connecting the cap on the top to the central electrode might have gone open circuit so that you would have measured zero Ohms with the multi-meter.
Title: Re: spark plugs
Post by: JulianS on 19 February, 2017, 19:52:50
An ohm meter is useful for testing the rsistor in a resistor type plug.

For non resistor plugs not  a useful test. Try it on a new plug and see what you get - probably open circuit.

The best test for a plug is by substitution they are cheap enough. It how they work in a hot engine under combustion pressure which matters.