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Intermittent Ignition fault

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Intermittent Ignition fault

Postby Dee Wright » Tue May 10, 2022 9:43 pm

Evening all, sorry if this has been covered before, but i am still learning about My 1959 early series 2 Li125.
It runs on original ignition, points etc.
Being stubborn i refuse to take the easy route and convert to a 12 v electronic system.
Running well, starts easy, plug is a great tan colour.
Here is the problem, after a decent run of a few miles i will come to a stop and the engine will cut out, no splutter, no misfire, engine just stops.
I have changed the plug and cap, also the HT lead.
After say 20 minutes i will get a spark, with plug out, replace everything and off we go as if nothing has happens.
This is leading me to a HT coil getting hot. Then cooling down, hence the return of a spark.
Is my assumption correct ?
I have a spare coil which i intend to fit, this came off my partners Li150 series 2. I noticed that there are 3 washers on each terminal, 2 look like alloy and one is a small spring washer. What is the correct fitment for the leads, is it above the alloy washers or between. Sorry if this is a numpty question but electrickery is not my best subject.
Cheers Dee
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Re: Intermittent Ignition fault

Postby Warkton Tornado No.1 » Tue May 10, 2022 11:01 pm

Nothing fundamentally wrong with well maintained contact breakers, so I'd advise against change. Remember, they're only 'original' once.

To make the best of points ignition, a non-suppressed cap is best & plug manufacturer is a personal choice. I've experienced too many duff NGK's & have switched back to Champion.

Your problem sounds like classic blocked vent in the fuel cap, or fuel starvation, possibly due to a sticking float, unless I've misinterpreted your Post :?: Or are you saying that "After say 20 minutes I will get a spark" but in the preceding 20 minutes there is no spark?
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Re: Intermittent Ignition fault

Postby Fast n Furious » Tue May 10, 2022 11:35 pm

If you are loosing the spark when the engine is hot, then it could be a faulty LT coil on the stator. This is a classic issue with electronic stators for capacitive discharge ignitions, but I suppose it could also happen to inductive points stators especially if it's over 60 yrs old! Check the earth connection of this coil where it is bonded to the stator laminates.
More likely though, the cause is a duff points condenser. When these get old, they become very susceptible to shorting out when they get hot. When the engine cools down, the spark returns. It's a £12 part. Just replace it.
Hope this helps.
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Re: Intermittent Ignition fault

Postby MickYork » Wed May 11, 2022 7:40 am

Are you sure there's no spark ? unfortunately sometimes the spark can't be seen and a finger up the cap is sometimes required :shock:

The point being, if it isn't the spark then fuel shortage would be a good option, with a sticking float or blocked breather cap hole giving the symptoms you describe.
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Re: Intermittent Ignition fault

Postby lofty » Wed May 11, 2022 8:41 am

I had a similar problem a few years ago, and after trying several things (most mentioned above, eg check points settings, check connections in stator, replace condensor) in the end, it was the coil, so changing that for a known good one it a pretty easy first step..

regarding terminals, i dont think it matters too much the order of washers, but i would have (from coil upwards) plain, spade connector, plain, spring, nut..
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