30 replies to this topic

[Rubbershorts]

Hi guys, just been for a 25 mile spin, after changing plugs, leads etc, on West Yorkshires finest twisty country lanes. Had a peek at the plugs when I returned. I'm not too sure. I'm also no expert so would appreciate any thoughts on here concerning their colour. Their position from the radiator is numbered. 1 being next to the radiator.

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[weef]

All the insulators are a similar colour, there are slight variations but nothing too dramatic looking.

Your trip was maybe not long enough on new plugs to get a good guide, the mixture looks too lean to me.

A light coffee colour is preferable, you do not want too lean a mixture, maybe screw the jet down one flat and see what the change is.

[Rubbershorts]

All the insulators are a similar colour, there are slight variations but nothing too dramatic looking.
Your trip was maybe not long enough on new plugs to get a good guide, the mixture looks too lean to me.
A light coffee colour is preferable, you do not want too lean a mixture, maybe screw the jet down one flat and see what the change is.

Thanks. What would one flat be? And is that clockwise?

[Rubbershorts]

All the insulators are a similar colour, there are slight variations but nothing too dramatic looking.
Your trip was maybe not long enough on new plugs to get a good guide, the mixture looks too lean to me.
A light coffee colour is preferable, you do not want too lean a mixture, maybe screw the jet down one flat and see what the change is.

Thanks. What would one flat be? And is that clockwise?

Ah, just looked on line, it's a nut. So one flat anti clockwise would lift the needle allowing more fuel through?

[weef]

You want to screw the nut clockwise looking down from the top. This "unscrewing" moves the jet tube down the taper of the needle making for a richer mixture

[imack]

The adjusting nut or screw (depending on carb type) is only for setting the idle mixture, not for adjusting the mixture across the rev range. You need a change of needle profile for that.

[Rubbershorts]

The adjusting nut or screw (depending on carb type) is only for setting the idle mixture, not for adjusting the mixture across the rev range. You need a change of needle profile for that.

I'm confused now. You'd have to change the needle, for another one, to make the mixture less lean?

[Rubbershorts]

The adjusting nut or screw (depending on carb type) is only for setting the idle mixture, not for adjusting the mixture across the rev range. You need a change of needle profile for that.

I'm confused now. You'd have to change the needle, for another one, to make the mixture less lean? Isn't changing the needle for large changes, whereas the adjustment using the nut is fine tuning?

[absx2]

If it`s running well I would leave it alone, yes you could say it`s a tiny bit lean but I`d be well happy with that plug colour.

[Rubbershorts]

If it`s running well I would leave it alone, yes you could say it`s a tiny bit lean but I`d be well happy with that plug colour.

😎👍

[weef]

By lowering the jet tube you change the possition farther down the needle taper, thus making the mixture richer, for the same needle lift .

No need to change the needle unless things are seriously wrong which in your case I suspect that they are not.

The carburettor piston lift will be the same for certain throttle possitions its just the fact that the starting point is lower that exposes more of the needle taper so the mixture is richer over the whole range.

[ACDodd]

What size engine and what heat range plug are you running?
I am seeing a little rich on the fueling here.


Below is a set of plugs from a perfectly tuned 998 with oil burning on one cylinder only. It shows the colour to aim for on the 3 plugs that look clean. This is after 300miles of motorway running.

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Edited by ACDodd, 27 July 2024 - 11:13 AM.

[68+86auto]

Looks rich to me too. I'm not sure how anyone says that looks lean. Probably because everyone sets their mixture way too rich.

 

I don't tune by plug colours so maybe I just don't know what I'm talking about but I expect to see exactly what ACDodd has shown.

[Rubbershorts]

What size engine and what heat range plug are you running?
I am seeing a little rich on the fueling here.


Below is a set of plugs from a perfectly tuned 998 with oil burning on one cylinder only. It shows the colour to aim for on the 3 plugs that look clean. This is after 300miles of motorway running.

Hi AC, it's a 1275 and the plugs are Lucas LPL004.

[ACDodd]

I see a different colour on each plug that usually means the ignition system is not optimised. What coil is it running (resistance) and what dizzy type are you using? Is there a ballast wire fitted? Change them to a set of NGK BP6ES. Gap them before fitting.


AC