No Spark

[Lambr62]

Hi,
How do I bypass ignition switch? Ive lost spark and amongst the usual things to check I want to make sure ignition switch is not at fault before I start pulling flywheel off to check stator etc. Thanks in advance for any help.

[missing lynx]

Remove the green wires from the cdi

[MK Monty]

Only the green coming from the loom, you still need the green from the stator to the CDI

[MickYork]

have you got a cdi or is it points ?

[Lambr62]

Sorry its electronic ignition.

[MickYork]

The switch shorts the cdi to earth, so, as has been said, disconnect the green loom wire on the cdi, leaving the green stator wire connected.

[Lambr62]

Have just checked stator wires for resistance as per Stickys book see below. Not sure if this is ok or not? Have tried green wire from stator to chassis earth and I get a spark when I kick over.

white wire to chassis earth = 0.4 ohms (should be less than 0.1 ohm)
white wire & Red wire = 92 ohms (should be 95 - 120 ohms)
white wire & green wire = 544 ohms (should be 450- 540 ohms)

[CHRIS in MARGATE]

Your earth should ideally be <0.1 ohms. I guess the difference will be the quality of the meter or the resistance of your test leads.
Your tests point toward CDI, HT Lead or plug cap.

[Lambr62]

Some more background information as follows : Original problem up to half throttle ok in each gear, at half to full throttle no power thought it was 4 stroking problem maybe carburation or electrical.

Checked ignition timing with strobe as I hadn't checked this since engine rebuild where I converted to electronic ignition. Strobed ok at 19 deg setting.

Found a leak on exhaust to manifold joint tighten up bracket as not as tight as should be.

by coincidence problem went revved clean through to full throttle. Went out yesterday was ok through all gears after around 20 mins problem came back and I had a misfire.

got back home on drive scooter idling then just cut out couldn't restart. Checked plug against engine mount no spark.

[Hornbyfrog123]

It sounds like your HT coil, runs ok at low revs but drops out at higher revs. Had the same problem. Could be wrong but worth checking.

[Lambr62]

Hi Hornby,
By that I guess you mean CDI in my case?

[MickYork]

HT coil is on the stator. Plenty of options......new stator or just change the HT coil.....or change to a cdi that works off the lighting coils or use a DC cdi that is powered from a battery.

The options are related to your wallet and ability/tools to do the work.

[Lambr62]

Ok thanks for replies

[Fast n Furious]

This sounds like a classic failing LT stator coil. Resistance measurement is unlikely to show up a fault here.
Quite often, the engine will develop a rev limiting situation before eventually quitting altogether when the engine gets warm.
Sometimes, a worn mag bearing is enough to upset the pickup alignment leading to a similar situation.

[CHRIS in MARGATE]

I would have put money on it being the most common Lambretta failure, namely the LT coil on the stator plate but you started your post with "no spark". You have now said you have spark when holding the green from the stator to earth which most likely would indicate a fault further along the circuit.
Those pesky LT coils are notorious for breaking down when warm and under load and quite often on this forum an original poster will come back and report after trying everything and 3 pages of suggestions, that it was in fact the stator all along. So be prepared.