Modern Vespa

Hi all,

I own a motorcycle workshop and this LX 3V 125cc injection is driving me crazy...

I have cleaned throttle body, there is a good spark (replaced spark plug), checked HT LEAD and Coil all are good, air filter good, NEW INJECTOR just installed...

There is no error or dash light.

It doesn't start easy without a little throttle is impossible, when it starts, it stays in good idle for about 25 seconds then it starts to decrease the idle and almost off itself,.when i open the throttle it sputters and doesn't want to, opens and closes for like 5 6 times then it gets full throttle and if you keep it full it runs as long as you don't release it because it will shuts down itself...

What it could be? Anyone experienced...

how many miles?

have you cleaned the air filter, and checked that the filter box is sealed and there are no vacuum leaks in the intake system?

have you checked the valve clearances?

Hi,

1. Try to check the ECU, replace and see if it works. I needed to replace my ECU on my LX125 2V, but it did not recognize my keys in my case.

2. I would check timing system, could be wrong setting on the chain.
When its cold it will work, when it change timing for different fuel mixture on the ECU to normal engine temp it will struggle to work.
I had similar when i move chain 2 teeth in the wrong position.

Page 159
https://manuals.wotmeworry.org.uk/Vespa/LX125-150ie%203v/LX-S-125-150-3v-ie.pdf

Here is the video showing exactly what I am taking about.

I've checked

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It sounds like it's lacking of fuel or ignition.
I had this when spark plug cap was loose, misfiring happened.

Check the injector. Maybe it's clogged from low quality of fuel. Maybe fuel pump is weak.
Can you smell fuel from the exhaust?
If so, than ignition problem, spark plug or coil maybe.

You did replace injector and spark plug

Someone recently had a visible good spark, but their Vespa wouldn't run right, until they tried another plug. Might be worth seeing if the spark plug is gapped correctly?

Not sure about the LX, but the current Primavera / Sprint 3v engines are meant to have the valves adjusted at 600 miles and then I believe every couple of years / 6000 miles after that. A lot of people try often undertake their own oil changes and often ignore the valve adjustments until they become quite far out.