Reading Spark Plugs

So can anybody tell me what the condition of my spark plugs mean in relation to the running of my engine?

Is it running too rich or something else?

 

Looks lean to me.

 

Lean, interesting! I thought number 2 looked full of carbon but 3 and 4 could be lean.

 

To be fair, I think with modern petrol some of the old ideas (about reading plug colour) maybe don't apply quite so much. Also depends on the heat range of the plugs currently fitted. Your insulators just look a little too white for my personal taste but maybe some of the guys with AFR meters can chip in as they will know if they're running rich or lean.

Here's one of mine for comparison, it's a NGK B5ES (long reach) in a stock T1 1600DP engine.

 

I know mine is always rich.
I agree, there's not much to be gained looking unless something extreme is going on.
Same plugs (not long reach version) on a 2.4l type-4.

 

I was reading some stuff on tuning bike engines and apparently you need to run at a constant RPM and then cut the engine dead as otherwise idling will affect the colour.

 

The ones I took out (in the pics) are NGK B5H S not sure if they are long reach or not, in a T1 1600. I’m replacing them with Bosch W8 AC.

 

Nothing extreme that I know of just read somewhere they could be good indicator engine health but take the point that modern fuels may affect it.

 

People reading spark plugs are interested in what's been occurring foot to the floor and/or at high speed under high load...so, unless you do that, stop and look at them I don't think you'll find anything out.

If for example your lean main jet drove you along the motorway then your rich idle jet sooted up the plugs between the slip road and home you could be lulled into a false sense of security.

 

I've been doing an online crash course in tuning Mikuni carbs, I do love the internet for this sort of thing

 

Cheers. This all started because of it misfiring/backfiring so started to investigate. Fairly sure it was due to a damaged HT lead but started digging. Always a dangerous thing to do!

 

I do it constantly.

 

Was the damaged HT lead on plug no 2 by any chance.

 

It was which probably explains the carbon.

 

Exactly. The rest look ok.

 

Ok another question. Why are you using long reach plugs in a stock engine? It looks as though I have a Mexican sump (not sure if the cylinder is Mexican) and I’m wondering if I should be using long reach hence the reason it is running lean.

 

Sump is irrelevant. It’s the heads. Check how many threads there are @zedders will then know the answer. Use a paper clip or similar. Don’t drop it in though

 

I'm running Mexican heads which require the long reach plugs.

 

So it’s stamped on the heads? Will take a look in the morning, if I’ve not already got a photo, safer than using a paper clip as I’m always dropping screws.

 

if you've just pulled them out after a short drive, the plug readings won't tell you much. Ideally you want to be driving the bus quite hard for half an hour or so, so it's been under load and at full working temperature then find a nice quiet flat stretch of road where you can spin it up to around 3000 RPM in third gear then push the clutch in and coast to a stop without blipping the throttle. this will give you the most accurate plug reading.

I seem to remember 15 thread valleys for a 1/2 plug which would put the unthreaded edge flush with the chamber hole but don't hold me to that



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