Ignition testing (spark plug pictures)

[Scruffy]

Hey fellas. I've got a NC24. Sometimes it doesn't run on all cyllinders, particularly it happens on a steep uphill.

When looking up ignition tests this are the tests I've found:
- coil primary resistance
- coil secondary resistance
- coil secondary resistance with HT lead attached ("secondary winding with plug cap" resistance in spec sheet)
- Watch HT leads in the dark and look for glowing (bad insulation)
- Pull off leads with rubber gloves one at a time while engine running and listen to change in pitch. (won't damage bike?)
- Remove one spark plug, connect to HT lead and hold plug body on frame and look at spark. (will this make a mess out of the open cylinder?)

I'll give these a try, have I missed anything?

[CMSMJ1]

Welcome..

You sure it is electrical? Why?

If it runs, it runs..the sparks don't change if the bike is under load unless the plugs are knackered...but even I'd be putting variable performance at the feet of the fuelling.

Has it always done this? Has anything changed on the bike? Is it totally standard (have you checked) in the carb settings?

We'll sort you out...

[thunderace]

I'd say it's more likely fuelling as well. From my limited and recent experience, my first step would be to strip and clean the carbs.

[Scruffy]

Thanks :)

I've had the carbs serviced and synced. Carbs are standard.
Plugs could be knackered... Could you please elaborate on unplugging a HT lead while bike is running, can this cause damage?
What about cranking the bike with a plug out to look at the spark quality, can I just place a rag over the hole?

[thunderace]

What plugs are fitted? They should be C8EH-9 standard (quite rare) or CR8EH-9. I had problems with mine only yesterday and it turned out to be incorrect plugs fitted.

BTW, testing for spark with an open cylinder is fine, don't worry about plugging it.

[CMSMJ1]

Carbs serviced and synced means nothing on a 22+ year old bike.

Someone, sometime would have had them in pieces..and I'd be amazed if they were still in a bog standard setting.

If you cannot resolve this with plugs then check the carbs yourself..the only way to be sure.

with plugs - have you checked them to see the condition of the tips? A plug not firing will be very black, or wet, or both.

try swapping them around and see if the poorly cylnder follows the plug.

Saying that, if it only happens under load then I still don't think it is plugs or electrical - unless the battery is also weak and the poor running coincides with the charge getting low, just as you arrive at the hilly part of your route.

Have a read of a thread by "smoky" in this section. He has an NC24 that had fried the generator..could easily be this.

The HT leads usually either work or they don't - nothing intermittent about them

[Neosophist]

Interesting idea on the coils.

Uphill the bike would be under more load and the coils might be breaking down. However, as everyone else has said, this is quite rare on these bikes.

I'd check the following.

1. Electrical system (altenator / reg-rec and battery) there notoriously weak on these systems and when they break down the bike can run rough.

2. Plugs, remove them and make sure there the right plugs and are in good condition (no obvious signs of electrodes falling off)

3. Carbs / Fuelling.. I posted a detailed thread the other day about what jets / etc should be where in the carbs. Quite often they get mixed up. However, performing bad on an incline might be due to float heights rather than jets as it'd run bad all the while.

[Scruffy]

A previous mech put racing plugs in my bike, which are inappropriate for what I use the bike for.

See pics below
These are my back 2 spark plugs (left on the left, right on the right)
They're NGK CR9EH9 (racing plugs), but I do 90% short duration town riding.
I just try ride fuckin hard to make up for that, ensuring the plugs get nice and hot :)
Carbs have standard float heights etc, but I think the jets might not be 100% standard, dunno though, I have the idle mix at 2.5 turns out.
In the first pic I had only wiped the right one, the 2nd pic I wiped the left one too.




Both of the plugs were gapped too wide. I'd guess about 0.35mm at least.
I re-gapped them to about 0.3mm.
Spec says gap should be between 0.2 and 0.3mm. I've read that wider gaps make hotter sparks, so I figured 0.3mm is good?
Bike is running good 80% of the time, but occasionally power disappears a bit, and it sounds a bit like its not running on all 4 cyls.

Should I change to NGK C8EH8? (standard plugs)
Should I lean the idle mix on the left plug a bit?

I did the test where u run the plug outside the bike, with the body jumper cabled to the frame. Sparks looked good on both sides.
Soon I'll take the front ones out for you guys to see.

[Scruffy]

Wow, bike runs so much better with the back spark plugs at 0.3mm gap. (was too wide before)
Pulls hard now!
Thinking of lowering it some more even, like 0.22mm or so.
What spark gap do you fellas run?
This really makes me want to check my spark gap on the front ones now.