This news post if a general information post for Lambretta LC and LD Points; Magneto; Stator; Coil; Spark Plug
Posted 21 May 2020 and may be added to or modified:
I created this page / post for my own information and guidance and as a result of spending much time to try to get a pre 54/55 (HT bakerlite setup used to spark plug Lambretta / Teleflex Gear Chnage Cable) . It also highlights the differences found in the various Lambretta (mainly first edition) books.
It was created as a result of me installing a stator plate into a Lambretta that had not been running for many years and had been tampered with / dismantled in this area. It was unclear what position to install the stator plate to begin with (for example – start off in the center / far left / far right). One Lambretta manual I have and YouTube videos state that if you ever remove the stator plate, make sure you mark it, so that you can line up the marking and install it back into the same area. This information does not help for rebuilds where the stator plate has been removed and you have no idea where to start.
Once you have started the Lambretta, you can then start using the timing light / strobe and move the stator plate slightly to the exact position, or advance (improve performance), or retard the timing.
Stator Plate (The Book of Lambretta – Page 98 & 99):
Rotation of the stator clockwise will advance the spark, i.e. cause the plug to fire earlier and rotation anticlockwise will retard the spark. The possible range of adjustment of the stator plate is a matter of some 20 degrees.
Stator Plate Advance and Retarded Settings( Lambretta Main Features / Repair Manual Book – 125LD / 150LD MK3 – Page 66 ):
- For readings HIGHER than 4.60mm (26″) rotate stator plate clockwise
- For readings LOWER than 4.00mm (24″) rotate stator plate clockwise
Lambretta LD & LC Stator Plate Explained
Summary: Ignition advanced may aid in more power. However, too much advance and the gas expansion will try to push the piston down while the crank is pushing it up. Too little advance or retarding the ignition will push the piston down as the crank is pulling it down which will reduce the force of the gas expansion.
You want the greatest gas expansion when the piston is at the top of it’s travel. Combustion takes a little time and it needs to be initiated just prior to the piston being at top dead centre, hence you may therfore want to have an ignition advance.
My investigation to date:
In theory, I believe the Lambretta should start up no matter where, or what position the stator plate is installed. in summary, the stator plate can be used to retard or advance the timing. However, you need to get the Lambretta started first before you can start reviewing this area and if it’s installed correctly.
Investigation in this area shows that timing can be set in one position and the stator plate can be used and modified to within 20 degrees (+ or – 10 degrees in summary) to either advance or retard the timing. Starting / installing the stator plate in the centre to start with did not seem to help me with two of my Lambrettas. these two would not start at all, unless I installed / move the stator plate anticlockwise as far as it would go, to start with and then review the timing settings and modify (slightly clockwise!).
One Lambretta I looked at was starting via a bakerlite (Pre 54/55 Lambretta) HT block and an external coil (bypassing the bakerlite solution, but still taking a feed from the ignition (left side coil / green cable) ) had to be installed before I could get a spark / electric shock from the spark plug.
Also, I needed to closely monitor the points gap settings throughout this install.
Lastly, I found that the carburettor I was using, was providing too much fuel and this also impacted the Lambretta in not starting.
In summary, it was a tricky one for me to fault diagnose. Once all the issues above were addressed, I finally managed to kick-start this Lambretta (Pre 1954/1955 teleflex gear change Lambretta), with two kicks.
Information on books and settings.
Spark plug and electrode (points) gap:
- I use between 0.45mm and 0.50mm most of the time. Other comments in books are as follows:
The Book of Lambretta (Page 83):
The contact breaker gap maximum opening should be about (Imperial) 0.016 to 0.020 in, although this is dependant on the timing setting.
Lambretta by Raymond Broad (Orange book) – (Page 25):
The sparking plug / breaker point gap are:
- C & LC Model – Imperial – 0.015 – 0.018
- D & LD Model – Imperial – 0.015 – 0.020
Lambretta LD MK3 Main Features / Repair Manual
- LD – Metric – 0.6mm / 0.7mm
Lambretta D-LD125 Service Manual (Page 33):
- Contact gap Imperial – 0.0138 – 0.019 or
- Contact gap Metric – 0.35 – 0.50mm
My notes to help me with feeler gauges (I use metric):
- Imperial – 0.015 – Metric – 0.38mm
- Imperial – 0.016 – Metric – 0.40mm
- Imperial – 0.018 – Metric – 0.45mm
- Imperial – 0.020 – Metric – 0.50mm
- Imperial – 0.023 – Metric – 0.60mm
Point to note: Most cheap Metric feeler gauges you buy online at around £3 go up to 1.00mm.
Spark Plug Gap Sizes, notes and possible issues:
A smaller gap will yield a short, intense spark and will usually make the engine real responsive. A wide gap creates a longer spark arc but without sufficient “juice” from your ignition system, (including amps), it can be weak and yellow in colour.
TDC / Timing / Stator Plate Information
Lambretta Service Man First Edition comments (Page 137):
No automatic advance and retard mechanism is fitted and the points should be set to break 28 degrees before top dead centre.
The Book of Lambretta (Page 98 & 99):
To time the spark plug correctly for it’s appearance at the plug, some 26 degrees before TDC, the position of the cam must be correctly arranged with respect to the contact breaker…. ect. Further small adjustment of the timing is provided for by making it possible to rotate the stator plate of the magneto, carrying the contact breaker assemble, either one way of the other over a small range.
MK3 125LD / 150LD
- For advance angle setting of 26″ – 4.60mm
- For advanced angle setting of 24″ – 4.00 mm
Lambretta by Raymond Broad (Orange book) – (Page 145):
The points should break at the left hand scribing on the flywheel, or about one and a quarter inch before TDC.
Spark Plug Information
NGK B7HS (short reach) spark plug
- B: Indicates 14mm thread diameter in the cylinder head. This diameter is used on all LC and LD Lambrettas
- 1-9: Indicates temperature (1 Hottest – 9 coldest).
- H: Indicates 12.7mm thread reach (approx 1/2″)
- S: Standard electrode
Spark plugs with a ‘BR’ denomination have a built-in resistance and are designed for use with delicate electronic equipment (such as SIP rev counter / speedo units). These need to be avoided for LD’s
Spark plugs with a ‘HS’ denomination are SHORT reach versions (Lambretta models manufactured between 1947-’57).