Scooter dies after 30-40 seconds

[Chewyboy]

Hi everyone
I have Lambretta S3 150 with electronic ignition and dellorto 18 carb. Problem is this- it starts up fine but dies after 30-40 seconds. I have by passed the tank - still the same. Changed float, red tipped valve, hinge and bowl. I have sanded the inside of the bowl and the outside of the float - still the same. It's just like the carb is filling up then the valve is sticking in the up position and when it's used the fuel in the carb it cuts out, leave it for a minute and kicks up again. Could I be barking up the wrong tree and could it be electrical.
Any comments appreciated.
Thanks in anticipation.
Paul

[Fast n Furious]

Very possible it could be a failing LT coil on the stator plate. A very common problem.
To Check it out is real easy. Connect a digital multimeter ( If you haven't got one then borrow one or buy a chep'un off tinterweb) that is set to read 250+V AC. Connect one of the leads to the igntion green wire on the CDI and the other to ground. You should measure around 60V at tickover and about 200V when revved out. If the reading is erratic or drops off to nothing before the engine stops rotating, then this is your problem.

[CHRIS in MARGATE]

Agreed. If all carb and breather checks complete then as stated potentially the LT Coil. It nearly always is.

[Den08]

I have been going through this for about 18 months on and off.
When cold it was a barsteward to start once warm no problem,
it was pointing to choke issues, all the mates and forums said!!
messed around with that, still the same check you stater they said
Claen your tank they said take your fuel cap off they said check your timing
Bear in mind all this has to be done over two days to allow for the cooling
Down because once warm no problem, so trolling the internet again
Found a thread on a rev and go site, exactly same simtoms Turns out to be Cdi can’t be
I thought they either work or not, wrong put a new one on problem gone
Not saying thats your problem, but if you can borrow or have a spare one
Give it a go.

[Chewyboy]

Thanks guys, will crack on with it today and let you know.

[Chewyboy]

@fastandfurious
Did the static checks as per sticky's manual all ok. Did the running test as you advised and was reading 100v at tickover and 140v when revved out. New stator needed you think? Oh also tried new CDI to no avail.

[grandpa]

HI Chewyboy/Den08
[quoteWhen cold it was a barsteward to start once warm no problem,][/quote]

Assuming ignition and carburettor are ok,you could have an air leak resulting in a weak mixture and once warmed up the leak is sealed by heat expansion.
Low compression also causes problems that disappear once warmed up
Try a leak and compression test

good luck
Grandpa

[Fast n Furious]

@fastandfurious
Did the static checks as per sticky's manual all ok. Did the running test as you advised and was reading 100v at tickover and 140v when revved out. New stator needed you think? Oh also tried new CDI to no avail.

Those readings are not what I would expect, but more importantly, what happened to the reading as the engine died? If it dropped to zero or near zero as you were coasting down then yes the LT coil is goosed.
If the reading showed a relatively healthy voltage as the engine died and you were still coasting down, then the problem is something else.

This test just proves if the LT coil is good or not. This has to be an "on the road test". Its the readings on the meter during the coasting down period after the engine dies that counts.

[Adam_Winstone]

Is this running an old standard exhaust? Carbon or broken up internals blocking the exhaust tailpipe can do this too, as can a failing ignition switch (although being an LI it could still be a push kill).

To address the above points, stick a bent wire coat hanger up the tailpipe and give it a good poke around, then unplug the loom from the green that goes to the CDI (leave the stator green connected to CDI).

On the note of red tipped float needles... the Jetex needle tends to be longer than the Dellorto, meaning it can cause fuel starvation issues. The Dellorto red tipped could also be slightly longer than the original black tipped item. If you still have the black one then it might be best to replace it so that you can eliminate it as being part of the problem.

I would also do all of the ignition component checks that others have suggested.

Good luck getting it sorted.

Adam

[sunrisemac]

It's just like the carb is filling up then the valve is sticking in the up position and when it's used the fuel in the carb it cuts out, leave it for a minute and kicks up again.

Have you tried turning fuel tap off immediately it stops then taken float bowl off to see if there's any fuel in it?

[Chewyboy]

Hi everyone
Thanks for all the advice. Put on a different stator and problem cured. So bought a BGM stator and it's now fitted and running perfectly. Old stator was an AF and had done 500 miles tops. Thanks once again!

[Fast n Furious]

500 miles......... Not bad for one of those IMO. I remember fitting one that didn't get 20 miles. Don't expect the BGM to be much better.
The way forward is to do as HxPaul has suggested on a similar thread subject which is to fit a " Readspeed Lukas CDI and run it from your lighting coils,it bypasses your duff LT coil altogether." I'll just add:- Other brands may be available?
I use a programmable DC driven CDI which works similar to the Lukas and the spark is perfect. First kick starter 99% of the time and the spark plug just seems to last forever like it's supposed to.
Make sure that your ignition HT only has the 5K ohms of resistance in one component. The HT lead, the plug cap, or the plug. Any more than one will seriously degrade the strength of the spark, which will primarily affect starting.