LCGB Forums

Morning forum people,

I kinda guess this is a stupid time to ask this question, the words horse, bolted, stable and door spring to mind

I brought a sterling exhaust to use with my standard S3 125 special. After the exhaust had launguished in the garage for a year or so decided to put it on the scoot, only to find that the kickstart won't return to its rest position without fouling the expansion can, and a friend telling me that I couldn't use it anyway on a standard (unmodified) engine.

Any advice regarding either issue much appreciated

You can use it but check the plug to ensure jetting is correct. If the colour of the plug is in the slightest bit lighter than mocha chocolate brown then increase your main jet by anything from 2 to 5 sizes bigger.
Fouling the kickstart is a normal problem and something has to be fettled. You could mark up where it's catching and take a little piece of the kickstart tab off or you could gently "persuade" the exhaust.

Cheers Chris

I'll try to manipulate the exhaust before attacking the kickstart

Gino_Lamberto wrote:Cheers Chris

I'll try to manipulate the exhaust before attacking the kickstart

Fine but don't put any part of the exhaust or bracketry under any stress or it will break when riding.

Rich Oswald wrote:

Gino_Lamberto wrote:Cheers Chris

I'll try to manipulate the exhaust before attacking the kickstart

Fine but don't put any part of the exhaust or bracketry under any stress or it will break when riding.

Ok Rich, duly noted

the sterling is a revy peaky pipe and you will find the way the scoot drives will be different to how it did previously (assuming you had a standard type box pipe on ). I seem to recall having to mess with the kick start on a gp with the same pipe to prevent it fouling at rest. iirc I extended the rubber stop in side case a few mm so as to cure this .good luck. bazza

Gino don't take nowt off the kickstart!!!! that's the last thing you want breaking due to any fettling, there should be enough movement on the exhaust, if not fettle that NOT the kickstart.
as regarding the carb/plug, only through plug chops will you determine if the engines running weak, good luck

We will respectfully agree to disagree but IMHO no undue stresses will be placed on the remaining metal in the kickstart tab by removing a very small piece, 1-2mm from the very end.
Gently persuading the exhaust means "gently"
I fuss around for hours on scooters that I repair for people to ensure that everything fits perfectly because as Rich rightly says, any component in the exhaust system that is pulled up against its wishes will fail.
Plug chops for definite but read up or ask away.

Thanks for the replies, most appreciated

I have this morning loosened off the pipe from its ally mounting on the crankcase, and fitted the kickstart. To be fair there is now a minimum amount of interference, which will hopefully disappear when I fettle the ally mounting bracket and tighten back up again

This to be honest pales into insignificance, as just while trying to hold the scoot upright and pull the centre stand spring onto its location, I lost balance of the whole lot and it rolled over on to its side FFS

While I'm on, does anyone want to enlighten me to the meaning of plug chops ? Sorry to ask, but I'm such a newbie chopper

Welcome Gino.

A plug chop, as I understand & carry out, is the procedure of killing the engine whilst under load so that the spark plug may be removed & examined for it’s colour, thereby giving an indication of the fuelling @ that precise point.

Typically, the rider might select a stretch of quiet road, preferably with a slight uphill gradient, & cut the engine whilst accelerating in, say, third gear.

Simultaneous to that, the clutch will need pulling in & the rider should roll to a halt, preferably a lay-by, & then proceed to remove the (hot) sparkplug.

I won’t venture into giving my own ideas of ‘reading’ the plug as you will find better, visual information elsewhere on the internet. A brand new plug is not going to give you an accurate reading.

However, I will say that plug chops are a difficult thing to accomplish on a Lambretta with its key operated ignition, in particular.

Personally, in the past, I have fitted motorcycle type kill buttons to augment what’s in place or even toggle type switches in the choke lever hole when running Amal Mk I’s, just to be able to kill an engine effectively.

I hope you don’t take this response as patronising, but plug chops are invaluable & you’ve asked an excellent question. Unfortunately, the actual ‘plug chop’ is very difficult to perform effectively, in my opinion, without adding a ‘cheat’ or two…..

I hope this helps & doesn't put you off!

Good Luck!

Ok this is how I do it:
Mark up throttle grip so you can test fuelling at 3 or 4 throttle opening positions with masking tape or pen at the relevant points on the grip.
Warm the engine up and after a couple of miles on an empty street let the scooter run along in 3rd gear at the lowest opening indicated "approximately" by the marks on your throttle grip. Try and do this for 1/2 mile then kill the ignition, pull over and with a glove take plug out. Take a photo on your phone.
Now replace the plug; I use another; and repeat the exercise at mid throttle and again take the plug out and photograph it.
Lastly do this for about 3/4 mile at wide open throttle. If at any time the plug is white go back home with the choke on.
As a reassuring indicator complete the exercise with the choke on and you should see the plug black.

Compare plugs and/or photos when you get home. Anything on any of them that is lighter than mocha brown is a weak mixture at that point and needs addressing . Anything darker is too rich and will need looking at.

As a very rough guide if when riding you put the choke on the engine should splutter due to being over rich. If it doesn't splutter then the mixture is too weak.

The settings on your throttle relate to different carb openings and each opening is governed by a different circuit. If you want to get fussy and fine tune then check it at 4 different 1/4's.

Try and do this for 1/2 mile then kill the ignition,

Exactly how do you kill the ignition, declutch & hold the throttle @ your desired setting?

My road scoot has markings adjacent to the twistgrip for fine-tuning, but I have to rely upon a means of killing the ignition seperate to the mid mounted standard switch.

On a race scoot, you can do it with your knee if you have a central "Push off" kill switch (or two) on your bars, but how would Gino achieve this?

I'm intrigued. Perhaps I've been missing a trick all of these years....

This is how I do it; I would always welcome others' methods.
As I see it your method is spot on and precise without a shadow of a doubt but my method is the best way with what all, or almost all of us, have.
Once I have declutched and cut the ignition there is NO more burn. This method has served me well since the first scooter I built and tuned to take to the IOM in 1970 (I didn't get there BTW) and has never failed me.

I would suggest, but I am open to be being convinced otherwise, that shutting the throttle by letting go denies any significant fuel flow to wash the now extinguished spark and displaying a false result.

Worthy of further debate.
Regards
Chris

Chris.

More recently than you, having only owned continuously one Lambretta or more since 1973, I believe that the whole point of the plug chop is to enable an accurate reading @ the precise moment the engine is killed. That is, under load, not several milliseconds after.

However, although that is my own belief, I’m not clever enough to have come up with the procedure myself! Undoubtedly, I would have gleaned the advice from the writings of Dave Webster or been advised of it by other sporting scooterists of the day. Probably a combination of both. To this day, you will witness racers using the same method @ race tracks.

I’m sure that consistency is important & if your method works well for you, who am I to dispute your technique?

I’ll stick with mine though! Ha!

Gino Lamberto. Don't worry, we're not arguing; it's just healthy debate. The important thing is: put your exhaust on and try it. I trust you're not confused. As long as you make sure that your spark plug gives good feedback then all should be ok. That spark plug is your reference point along with your sense of smell, sound and feel.
Will it go any faster ? Under certain conditions it will feel faster but you will most probably have to rev through the gears a little longer and as long as it brings a broad grin to your face then it's mission accomplished !

Anybody else's plug chop methods ? We would love to hear.

Warkton Tornado No.1 wrote:

Try and do this for 1/2 mile then kill the ignition,

Exactly how do you kill the ignition, declutch & hold the throttle @ your desired setting?

My road scoot has markings adjacent to the twistgrip for fine-tuning, but I have to rely upon a means of killing the ignition seperate to the mid mounted standard switch.

On a race scoot, you can do it with your knee if you have a central "Push off" kill switch (or two) on your bars, but how would Gino achieve this?

I'm intrigued. Perhaps I've been missing a trick all of these years....

It's easy if you use a throttle that stays open at any given revs,just switch off the ignition and at that precise moment de-clutch.

You see I don't know now and I promise I am not being in any way argumentative. Does that ingress of fuel at WOT for a very quick burst that doesn't burn because there is no spark, cleanse the plug ? Surely at that moment you kill the spark you want NO fuel to get the truest reading ?

What are the combustion theories and facts ?

It's easy if you use a throttle that stays open at any given revs,just switch off the ignition and at that precise moment de-clutch.

Already on this forum, there has been some debate about self closing throttles. I remain in the camp that prefers ‘foolproof’

As for verification of the ‘preferred’ technique of plug-chops, it took me all of two seconds to find this:

http://www.tz250.com/forums/archive/ind ... -4395.html

Apart from the engine revs, I would reason verification enough for me....

Thats a bit dismissive and very self righteous.Wether its right or wrong to use a self closing throttle or,one that stays open ( which is the one that I use ).The fact still remains that if you use a throttle that remains open when you switch off and de-clutch you still get the result that you have been talking about.

Thats a bit dismissive and very self righteous.Wether its right or wrong to use a self closing throttle or,one that stays open ( which is the one that I use ).The fact still remains that if you use a throttle that remains open when you switch off and de-clutch you still get the result that you have been talking about.

It’s neither dismissive nor righteous to state my own opinion, surely?

Self closing throttles are a requirement for MOT & racing. So, simply by my own preference & some advocating, that makes me ‘righteous’ does it?

‘Sticks & stones’ aside, rather that, if you are right, than somebody inexperienced becoming the victim of an accident as the result of the throttle not snapping shut, as I did.

It won’t be on my conscience, however ‘righteous’ you may judge me to be.