Spark Plug confusion

[Andy M]

I've nearly finished restoring my 1960 Shooting Star. The mag was professionally overhauled a few months ago and new NGK B7ES plugs fitted. After getting the timing sorted she pretty much starts first kick, but had only been run in the garage or around the garden until recently.

The MoT was booked for this week and last weekend I did a couple of 5 mile fettling runs. All was well, except she was running a little lean at low throttle. On Sunday night I parked her up in the garage, started her up briefly and then left her overnight. No problems.

The next day I tried to start the bike to fine tune the carburation. Nothing. Not a splutter. I checked I had fuel and sparks by resting the plugs on the engine cases - a big fat spark on drive side and weaker but distinct one on the timing side. Over the next couple of days I worked through the options, but couldn't get the bike to even cough. Until I fitted  a couple of new NGK plugs and she started first kick and ran well. Praise be.  I carefully cleaned and checked the gaps in the old plugs and refitted them... nothing at all. New plugs...fine again.

So it would appear that after working just fine, overnight both plugs ended up not sparking when under compression. Can anyone explain how that would be? I've read some of the other posts about NGK plugs and I will try Champion ones now, but I won't to know if there is anything wrong with my bike that could be causing the plugs to fail?  Any thoughts?

Andy

[muskrat]

G'day Andy,
                i have had plugs not work straight out of the box. Funny I prefer NGK to Champions, each to their own.
Just remember the heat range for Champions is opposite to NGK. to go hotter with NGK go down #'s 6 is hotter than 7, with Champions 7 is hotter than 6. A hotter plug will burn a rich mixture better but may cause pre-ignition if too hot.
Cheers

[Andy M]

muskrat,

Ha, your preference for NGK over Champion is partly why I'm asking for opinions.

I've never really had any problems with plugs failing on previous japanese bikes, certainly without plenty of use. I've had the A7SS for about 10 years, it's been a protracted rebuild and hasn't run for any real distance in that time. At a previous stage I think I may also have had quite new NGK plugs failing on me  - but back then the mag wasn't running quite right and the timing was a bit off - so I'm not entirely sure.

Now everything appears to be good. The sun is shining and I'm itching to get out. I nearly wept when I had to cancel the MoT 'cos after weeks of regular starting it had refused! And this is the clearest example I've had of plugs failing, which I can't explain. And both plugs fail at the same time??

I'm hoping that the 'NGK don't work well in some Brit bikes' comments I've read are correct and all my problems will disappear if I move to Champion, but I'm wondering if that is just wishful thinking and if I'm missing something more obvious.

Fingers crossed at this stage.
Andy

[Andrew]

I brought ngk plugs for my b31 within 15 mile the bike would not start, brought new again same outcome. changed over to champion runs allday long

cheers
andy

[bsa-bill]

started her up briefly and then left her overnight.

Short burst of life, not enough to clean the plugs but enough to soot them up, pretty sure it has to do with modern fuel which is fine for modern lean burn engines
All that said I have had trouble with NGK

[sinbad]

The plugs I have had problems with have been the resistive type with the letter R on.I broke one to see what the resistance was,As far as I could see it was a large air gap.I don't think these are suitable for the old bikes
Cheers.

[Andy M]

enough to soot them up

Could  be, but I did try to clean up the old plugs, first with a rag and some petrol and then by heating with a blowtorch. Didn't seem to help, but maybe I didn't get them clean enough.

[muskrat]

The way I look at it is, plugs are cheap and easy to change. So at the first sign of trouble, that's what I do.
Bill is right about short bursts not being good for them, more so colder ones.
Cheers

[LJ.]

Try NGK BP6HS.... I've always used these in both my A10s without any problems...

[roadrocker]

I've been having this plug problem on my 850 Commando, but only on the LH cylinder. The NGK will fail to spark after just one short run. Put in a new plug and its fine for a short time. Might have to try a Champion.
BTW I've changed coils, adjusted valves, gone up and down in plug heat range. What makes it strange, to me, is it runs fine until shut off, then when starting up next day, no spark on that plug.

[BSA_54A10]

1) modern standard plugs are sold at about break even and the QC on them is virtually nil.
The spark plug companies actually want them to fail prematurely so they can sell you the fix- $ 22 exotic alloy plugs on which they do make a good profit.
2) Modern supposed to be combustable fluids that we are forced to use contain a lot of electrically conductive elements.
These are virtually non combustible  in our old carburettor fitted engines.
If the plugs do not get hot enough to burn off the deposits from this light fuel oil before the highly volatile aromatics are burned off then it will leave a sticky brown/black residue on the plugs which is highly conductive under combustion pressures and your plugs will not fire. Tip some fuel into a saucer and leave it out in the sun. After a day or two there will be foul smelling sludge left in the saucer that will neither evaporate nor burn, and that is what you are trying to make your engine run on.
3) solution is to run the engine relatively hard as quickly as you can to build up heat in the head.
Do not leave the engine idling for extended periods either when cold or just before you close the engine down.
If you heat the threaded section of your plug red hot ( with an oxy or propane torch ) then remove the flame you will see a rich yellow flame issuing from the base of the insulator and it may burn for a good 5 to 10 minutes.
This is the "non combustible" portion of the fuel that has deposited on the plug and just like kerro ( parrafin to some ) you need to heat it around 400 Deg C before it will form a combustible vapor ( higher in your engine ).
If you continue to burn off your plugs then they can be used again.

I used to shut the fuel off on my bikes and leave the carb to run dry while the engine idled . Inevitably one in 3 or 4 times it would not restart. Since changing my stopping method to shutting off the fuel just before I need to stop then shutting down the engine from a faster speed with the magneto cut out, no more plug problems.
Even the ride on responds best to this method

[Andy M]

Spot on Trevor.

I got the blowtorch out on the faulty plugs until the centre electrode was glowing red and then kept going until the insulator was completely white again. Now they work just fine. At least I now understand the problem and will try to keep away from short runs and too much idling.

Thanks to everyone for their responses.

Cheers
Andy

[a101960]

It is interesting that this topic should be raised because I have suffered similar problems with plugs. On the first start after the winter lay up my bike started first kick (with petrol that had been in the tank for months). Yesterday The engine refused to start. After an hour I gave up. This morning I drained the carb, removed the plugs and cleaned them back to the metal using emery cloth. I put everything back together, and it started second kick. I noticed before the starting problem that I experienced yesterday, that starting had become less easy. The engine has always been a first or second kick starter until now. About 3-4 days ago it humiliated me in front of an audience in the car park. When it did eventually start it seemed to run fine. I had not used the bike since the car park fiasco until I went to use it yesterday. As a matter of interest I have NGK plugs fitted, and I cannot remember anything like that happening with Champion plugs. The lesson I have learned is to always now keep a spare set of plugs in the tool box.

John

[A10Boy]

I had this problem on my A10 when using B6's. If I started her and didn't open the air slide fully immediately it would foul the plugs or a single plug within about 20 seconds of start up while the plugs were cold. I changed to one grade hotter [B7] and all is well.

[BSA_54A10]

Yep,
Never even think of crossing the gutter unless I have a plug ( or two ) in the tool kit.
I fouled 6 plugs on one run several years ago, then ran on the last one, untouched for another 2 years.

The problem really is the "fuel" and not the plugs other than they were not designed to burn this rubbish.
Several members now drain their tanks after each run ( pop the fuel into the 4 wheeler ) then refill with fresh premium fuel each time they intend to go for a run.
Since following this reigeme none have had a stick of problems with their plugs.
They all have dicky tickers so none can afford the priviledge of jumping up & down on the starter for 1/2 hour.