LCGB Forums

Running in a new motor, at the stage of giving it the odd blast on to 3/4 throttle, it's nice and rich up to half throttle (4 strokes), clears when on to main jet, although I feel its still pretty rich, but that's a gut feel. When I get back after the ride and check the plug it looks initially nice and oily, apart from a small section, about 1/3 of the insulator looks grey (lean). I'm puzzled by this. Why would the colour not be uniform all the way around?

Logic says the heat at the top section of the insulator will be equal. There could be colour difference further down the insulator but again should be as a band around the plug, not 2/3 of the band being one colour and 1/3 another.

The plug is a NGK B9EG which is a cold racing spec type. I expect this will be where fingers are pointed

I am assuming its an alloy barrel?

Oh yes! BGM 225 + 60 mil crank (making it 230cc).
PHBH30 + BGM clubman
Varitronic set to 25 deg at fast idle

Probably a 9 is too cold for running in plus you may be too advanced , at 6k revs it will be around 20 degrees.

Use an old oily black plug to run in and for plug chops, will help to identify if lean. new plugs are hard to read.

Yep, and not only that but quite common for the plugs to colour one side more than another in ally kits.

Thanks for the replies. Interesting that alloy barrels are known for this. Trying to get my head around that. Do we know why this is?

I've a couple of old b7 plugs I can use for chopping so will give that go. Im clearly going to struggle with these B9 bad boys.

Timing: there is loads of conflicting info on varitronic tickover timing. I had it a degree or so more advanced to start with but all the power seemed to be there too soon, also got a bit hot on first long ride. Albeit with a B7 plug. Moved to 24 to 25 at fast idle, power comes in slightly higher in Rev range, feels better. I'll get it dynoed in another 50 miles or so. So we'll see where we end up after that.

I was told that the colouring was due to the cooling properties of the ally over cast and the fact that one side of all lambretta barrels is cooled more than the other.

As for using a b7, bin it! Dont use a b7 at all never mind for plug chops! B8 is the way forward

Donnie wrote:I was told that the colouring was due to the cooling properties of the ally over cast and the fact that one side of all lambretta barrels is cooled more than the other.

As for using a b7, bin it! Dont use a b7 at all never mind for plug chops! B8 is the way forward

Is alloys really that efficient at losing heat? Makes sense I suppose.

2 x B8 just ordered...they won't be old oily things though, but I suspect still far easier to read.

Cheers chaps.

Er, the advice about not using a B7 might be a bit misleading as it would depend a lot on the sort of motor you are running. I use
B8's myself but that is in an Avanti and a TS1. I would use a B7 if I was tootling around town and probably for normal running if it was a standard engine.

I agree and you might also be surprised that a B7 is one grade colder than the comparitive plug originally specified.
In my opinion I would fit B7 in standard engine when running in and the occasional short ride.
Personally I use B8 and B9 dependant on riding plans.

coaster wrote:Er, the advice about not using a B7 might be a bit misleading as it would depend a lot on the sort of motor you are running. I use
B8's myself but that is in an Avanti and a TS1. I would use a B7 if I was tootling around town and probably for normal running if it was a standard engine.

He's already said he's running a BGM 225 + 60 mil crank (making it 230cc).PHBH30 + BGM clubman etc.

So, I wouldn't have a B7 anywhere near that, not even for town riding when it's run in.

CHRIS in MARGATE wrote:I agree and you might also be surprised that a B7 is one grade colder than the comparitive plug originally specified.
In my opinion I would fit B7 in standard engine when running in and the occasional short ride.
Personally I use B8 and B9 dependant on riding plans.

Ummmm eh?

You are either saying a B7 is cooler than a B8 which it isn't or you are implying that he should be running a B6 in the first place???

No. By yesteryear standards the plug would be a B6.

Ah yeah, so yesteryear with a B6 then with his BGM 230 he'd be ok with a B7?

Yesteryear we would also be using leaded petrol, perhaps even 4-star, and not a sniff of detergents or ethanol... yesteryear no longer applies, nor do the high comp heads that we used to run either, not the timing...

... actually, why are we even still playing with old mopeds?!

As I see it there is no intrinsic difference between a 125 running on a 58 stroke to a 230 running on a 60 stroke crank. The second configuration is undeniably a more powerful engine but that doesn't mean that when set up correctly it will run any hotter. Bigger engines do not mean colder plugs. It's still a 2 stroke.
With regard to fuelling I think we have ALL turned back from 23 BTDC to somewhere a lot safer.
To all involved. I promise you I never set out in any forum debate to deliberately contradict; debate and constructive argument are healthy.
I truly laugh when people spend £16 a litre on 2 stroke because "it's better" or add octane booster or tell me that my piston holed after filling up with Shell in Essex because I was using an NGK B8, etc, etc.
So much of the information we ALL offer is based on personal experience and more often than not hunches because "my mate told me".
May we continue to expand the capabilities of our primitive engined, blow them up from time to time, and moan (really rejoice) when we rebuild them and make them even better.
Safe scootering to all.

^... sorry, I hope you didn't read into my response that I was being 'short' with anyone, that certainly wasn't my intention

Not for one moment Adam; I respect your wisdom.

I know lots but not everything and I learn something every week on here.

I'm having similar difficulties reading my plug.
Also running an alloy barrel.
Using a B9 because I thought it would foul up more and be easier to read.
Which part of the plug should we be using as a guide? The lighter meaning it's too weak or the darker which suggests it's as rich and boggy as it feels?