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plug colour

Taffy

Taffy

Joined Nov 2001
17K Posts | 774+
Ely, England
just thought i'd bring this up as a specialist subject to talk of.

sparks and i have been chatting and i mentioned that i found out that not all ignitions give a plug colour. so sparks this is what i had on my ducati:

i had the standard ducati pantah ignition system of a crank based two pick-ups and thyristor boxes, coils etc.

but when i went to a lucas rita it was half-speed shaft based, single pick up and 'hump' on the shaft so you still ended up with a wasted spark all the time! total loss ignition through a battery, i used a kwacker coil.

had a plug colour with the OEM ignition and nothing/zilch with the lucas rita. plug was ivory white all the time! and this was in the days of 98RON leaded fuel.

regards

Taffy
 
i gotta ask .... why would you have no colour with one and colour with the other ?

did you go with the lucas because it had a greater kick ?
 
This one has puzzled ma as well but I think it may be some thing to do with the supply voltage to the coil.
I am going to wind up a spare stator with a different winding spec to this if sheds any light on it. You can get strange things happening when there is to much voltage.

Regards

Sparks.
 
cheers steve

it's rare to have a high value thread on UHE but as usual it's all too much for most. let's talk abouit big tanks again!

regards

Taffy
 
I am interested in this thread Taffy, just wish I could contribute but alas I don`t know enough about it. I know that changing carb jetting can alter the plug colour but electrickery stuff is beyond me when it comes to plug colour.

So I have this tank I want to make bigger.................................................

Bill
 
I thought with all of the additives that are now in the fuel we use, you can't get a true reading from looking at a spark plug.
Maybe you can still get a general idea as to what is going on, not sure.

Please explain.
 
well we have two issues here. the first is that with unleaded you don't get a plug colour and the second is that with a change in ignition systems/bikes/models you do and you don't as well.

i'm not sure about the ignition systems but the fact that unleaded doesn't give a reliable plug colour has been known for 15-20 years. back in 91-92 we knew this.

also the heat range of the plug will change the plug colour. for instance a 7 will look lean when a 10 will look rich everywhere except at the tip.

we used to break the tailpipe and the downpipes apart and chack them at the join for the most reliable colour. so it's to do with the burn speed as well. i remember ignition timing having to be ******** to help a lot of engines.

but it's the difference in ignition systems that we're on about here and sparks has said that he'll look into it for us.

regards

Taffy
 
Are "plug chops" still necessary to get any sort of reading or is that just a 2T thing?
 
as said in a round about way - NO! you do an exhaust chop!

regards

Taffy
 
I don't know a whole lot about ignition stuff, but would it be possible that with a spark of higher intensity "or hotter" burns more efficiently and the fuel that would normally deposit on the plug and be left behind as "color" may be burned off, or prevented from becoming deposited in the first place? That would seem the logical explanation to me. I am interested in hearing what those who are better learned on the subject have to say.
 
Taffy said:
but when i went to a lucas rita it was half-speed shaft based, single pick up and 'hump' on the shaft so you still ended up with a wasted spark all the time! total loss ignition through a battery, i used a kwacker coil.

had a plug colour with the OEM ignition and nothing/zilch with the lucas rita. plug was ivory white all the time! and this was in the days of 98RON leaded fuel.

regards

Taffy
Click to expand...

Using high power ignition systems

Many of the more popular aftermarket ignition systems are of the capacitive discharge type. They store voltage, or accumulate it, until a point at which a trigger signal allows release of this more powerful spark. Companies like Mallory, MSD, Crane and Accel, to name a few, offer such systems.

They affect spark plugs in that they allow the gaps to be opened up to take advantage of the increased capacity. The theory is that the larger and the more intense the spark you are able to present to the air/fuel mixture, the more likely you will be to burn more fuel, and hence the more power you will make.

In reality, computer controlled engines do such a good job of lighting off the air/fuel mixture (as evidenced by the ultra-low emissions), added ignition capacity would do little to burn more fuel since the stock configuration is doing such a good job. Older non-computer controlled vehicles or those that have been modified with higher compression or boosted (nitrous, turbo, supercharged) engines can certainly take advantage of a more powerful ignition system.
 
Taffy said:
but when i went to a lucas rita it was half-speed shaft based, single pick up and 'hump' on the shaft so you still ended up with a wasted spark all the time! total loss ignition through a battery, i used a kwacker coil.

had a plug colour with the OEM ignition and nothing/zilch with the lucas rita. plug was ivory white all the time! and this was in the days of 98RON leaded fuel.

regards

Taffy
Click to expand...

Using high power ignition systems

Many of the more popular aftermarket ignition systems are of the capacitive discharge type. They store voltage, or accumulate it, until a point at which a trigger signal allows release of this more powerful spark. Companies like Mallory, MSD, Crane and Accel, to name a few, offer such systems.

They affect spark plugs in that they allow the gaps to be opened up to take advantage of the increased capacity. The theory is that the larger and the more intense the spark you are able to present to the air/fuel mixture, the more likely you will be to burn more fuel, and hence the more power you will make.

In reality, computer controlled engines do such a good job of lighting off the air/fuel mixture (as evidenced by the ultra-low emissions), added ignition capacity would do little to burn more fuel since the stock configuration is doing such a good job. Older non-computer controlled vehicles or those that have been modified with higher compression or boosted (nitrous, turbo, supercharged) engines can certainly take advantage of a more powerful ignition system.
 
RE: Re: plug colour

squizz

i'm talking about lucas rita from about 1975 and SEM from the bronze age. i only offer these coz that's all i know. the ducati OEM bosch gear and the SEM give a plug colour and are OEM on the respective machines i'm on about. the kokusan (i'm tild) and the lucas rita don't give a plug colour.

as i've said, sparks will look into it...

regards

Taffy
 
Re: RE: Re: plug colour

Taffy said:
squizz

i'm talking about lucas rita from about 1975 and SEM from the bronze age. i only offer these coz that's all i know. the ducati OEM bosch gear and the SEM give a plug colour and are OEM on the respective machines i'm on about. the kokusan (i'm tild) and the lucas rita don't give a plug colour.

as i've said, sparks will look into it...

regards

Taffy
Click to expand...

Hi Taffy,

A couple of my friends are drag racers. And other than color on the insulator, they tell me that they check to see how many threads of heat they are getting as well.

I'd appreciate your input on this.
 
RE: Re: RE: Re: plug colour

Taffy
I am interested in what you say about doing a exhaust chop instead of a plug chop.
Am i right in saying that if an alteration to the carb or the ignition circuit doing an exhaust chop would be the best way to go.
If so to make tuning easier could one modify the exhaust by maybe welding a boss on and have a bar of metal screwed into the exhaust, this could be quickly removed for a check.
Or am I talk daft.

Bill
 
RE: Re: RE: Re: plug colour

not heard of that one before. are you sure you haven't been suckered?

could be true but i copper grease mine and i don't run a silly fuel, turbo or supercharger so i'm not sure what i'm meant to be looking for?

as i say. undo the centre section of the exhaust when using UNleaded. also if you lean the jetting off enough to have a plug with no crud onit you can use it again and again. but a sooty plug is unable to self clean.

we haven't even got on to using '9's instead of '8's yet....

there's another story again!

regards

Taffy
 
It's a common way of reading plugs amongst these fellows. Ideally you're looking for about three threads of discoloration on the plug, as well as the insulator color.

Here is just one scenario, you can be so lean that your egt's are actually cool, then a slight enrichening causes the egt's to rise sharply.

If you are running rich, and are slowly going leaner, you will see the heat, or discoloration caused by the heat start moving up the threads of the plug.

I suggested this way of reading a plug in light of earlier posts in this thread wherein the insulator always stays white.
 
i get you. so you're actually trying to confirm that your jetting is all over the show? rich here and lean there?

i couldn't go on like that, i'd have to do something about it.

of course you could try half revs and a plug chop for a similar effect.

i have a fantastic story about a tuner called syd lawton who was a total legend on the GP and TT circuit. watched him get a plug colour at jurby airfiled (IOM) once. something else....

plug grade has not been touched on here and sparks you're being very quiet here...... come on now, don't be embarrassed!!!!!!!!

regards

Taffy
 
Hi Taffy,

Embarrassed no confused yes, I have to say that when I ran the new DMS needle like I said the difference was unbelievable instant twist and go where as the setting before was definitely to lean and a vague plug colour very slate grey, but after removing the plug on this run different colour altogether it is now a very light fornnie colour and on stripping the engine the inlet valves are the same colour too.
Taffy can you describe the actual colur you see on your plug we could all be suffering colour blindness lol. Syd Lawton a wizard I wonder what he would say about all this!!.

When I was doing the jetting on the Sherco 4t I had a similar problem but after having it on the dyno the plug colour on that wasn't to dissimilar to what I am now reading on the Husaberg.
Regarding plug heat range the 8 has always been the middle of the road has any body tried a 9 it wouldn't hurt anything.

And as for rewinding a different stator spec I didn't see much point at the moment with it being in bits, but i will experiment with this once up and running again.

Regards

Sparks.
 

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