Modern Vespa

Good day,
I purchased a 2003 lt150 4t at auction without keys. I removed the ignition and inserted a small wire connecting the 2 wires that ran to the ignition to bypass it. (Sort of like in the attached photo)
I then purchased and installed a cdi that bypasses the immobilizer system, or at least it claims to bypass it.
After installation of new cdi, I get a very strong spark and the scooter starts up and idles perfectly, but it will not accelerate past 10-15 mph and roughly 2000 rpms.
I imagine there is some sort of restriction because it doesn't bog down and die, it just cuts off any acceleration until it drops under 10-15 mph, or roughly 2000 rpms.
I also do not care about the immobilizer and just want the scooter to run and drive at it's potential.
Any help would be appreciated
Thanks in advance

I am certain some of the scooterwest videos mention this problem, don't think it's as simple as bypassing ignition switch, you have to reprogram chips and new keys,sounds like a limp mode or safety feature ie stealing bike good luck.

pics plz.

I'm guessing it, uhh, doesn't.

2K is the threshold for the immobilizer, so it's probably that's what you're up against.

as an aside, how long had it been sitting? any work done? does it start easy and idle well? what does it rev out on the center stand or just bog down?

Sorry couldn't resist.

Greasy 125,
I don't know how long it had been sitting prior to the 12-18 months I had it. I purchased it from someone who bought it at auction...
It starts easy and idles perfectly...
What would you like to see photos of?

It doesn't have a tachometer so I'm just guessing it is at 2000 rpms that it just cuts out, it does not bog down....

It doesn't have a center stand, only a kickstand

Wow that brigs back memories🤣💿💿

a pic of the CDI would be great.

so you're riding it and it just shuts off/stalls at 15~20mph?

have you cleaned the carb or rebuilt the fuel system?

Yes I've cleaned the car out and replaced the fuel lines so I know fuel is not the problem...
It's not like I can really ride it because it only revs up to about 2,000 rpms and 10 to 15 mph..
And when it reaches that point it just stops the engine just cuts out , it doesn't bog
It's like it's some sort of restriction as if the oil was low and the bike's not allowing it to go up past 2000 RPMs.

I'm going to guess that either the carb wasn't cleaned throughly enough or assembled incorrectly.

or that CDI is bunk.

you say in one sentence that it cuts out, and then in the next you say that it just won't rev out.

details matter, so try and be as precise and descriptive as possible.

such as: it starts up fine, it idles perfectly, when I give it throttle the rpms increase only up to a certain point and you can feel/hear it start to slow or load and then it's as if it hits a wall and the motor quits. it restarts easily and immediately and does the exact same thing, hot or cold.

My apologies for the confusion.
After installation of the aftermarket cdi, the scooter will start up and idle perfectly.
Twist the throttle and begin accelerating until it reaches a certain rpm level or speed, (roughly 2000 and 10 mph) and the acceleration is abruptly stopped, until the rpms fall below a certain threshold and it begins acceleration again, only to once again reach a certain rpm level and stop...it reminds me of riding a governed go kart at the local arcade/driving range/go cart place.
Something is telling the bike to stop accelerating, I don't know what it is. It's some kind of fault or restriction or safety feature....
The scooter does not have a center stand, and the code light on the dash doesn't turn on at all, I may have a burned out bulb, I'll check and update asap.
Is there something you have to do after replacing the cdi, such as turning the key on and off 4 times, or clicking your heels 3 times to get it out of this restricted or limp mode?
I've heard that if the oil level isn't correct the scooters won't go past a certain rpm, that's not the case here but is there something else I don't know?

that sounds like the CDI is bunk.

there is a coding procedure for CDI's with the immobilizer, but yours being aftermarket and not having a provision for it, then I think that's kind of a moot point.

the amount of oil in the sump wouldn't cause a cutting out issue, there's no pressure safety switch so they'll run it right up to redline before sticking a piston in the bore or hanging a valve.

It hits a rev limiter. I think these engines all have a rev limiter.
For some reason in your case the rev limiter comes in much too early. Should be at 7500 - 8000rpm, somewhere.

I think it has nothing to do with the immobilizer. The immobilizer does what its name says: immobilize your scooter: you cannot get it started.
In your case it starts and runs fine.

Or this CDI is just bad or it measures rpm's that are much higher than in reality.

You say you get strong spark.

Can you check how many sparks you get on 2 revolutions of the crankshaft? Because it is a 4T it should only be 1.
If it is then the CDI measures the revs correctly and you best replace it by a new one.

On some (early) modern Vespas, an unprogrammed (Virgin) CDI runs into a limiter at 2000 rpm.
The following excerpt is from a workshop manual for a 2007 Vespa LX 125/150 (Please check the workshop manual valid for your Vespa!):

"Non-programmed system
If the ignition system is not programmed, the engine can be started. However, the engine speed is limited to 2000 rpm and misfiring can be clearly heard when accelerating.
To program the system, the MAS-TER key (brown) and the OPERATION key (blue) must be used as follows:
- Insert the MASTER key into the ignition lock, turn to "ON" and hold in this position for 2 seconds (limit values: 1 ÷ 3 seconds).
- Insert all available black keys into the ignition lock one after the other and turn each one to "ON" for 2 seconds.
- Insert the MASTER key again and turn it to "ON" for 2 seconds.
You have a maximum of 10 seconds to change the keys.
A maximum of 7 operating keys (blue) can be stored during the same storage period.
The specified sequence and times must be adhered to, otherwise start again from the beginning.
Once the ignition electronics have been programmed, the ignition electronics and the transponder of the MAS-TER key interact inseparably.
If this interaction is maintained, additional operating keys can be saved after keys are lost, replaced, etc.
The old memory is deleted each time the key is saved.
If the operating key memory is lost, the ignition system must be checked carefully:
Resistance spark suppressor plug connector ~
5000 Ohm.
We recommend the use of spark suppressed spark plugs in any case (see illustration).

It would be great if you could check the codes for the web immobilizer: Immobilizer LED codes.

Does the LED for the immobilizer show a unprogrammed CDI?

Now there's me convinced that the spark happens every revolution - that it sparks on the exhaust stroke is of no consequence. BICBW...

all perfectly reasonable responses that would be relevant if it were a stock CDI

but it's aftermarket, so likelihood is that it doesn't have a rev limiter, and there is no provision for the immobilizer (as seen in pic).

my best *guess* is that it's for a leader motor and the voltage input/output is wrong, the unit is straight up bad out of the box, or there's something else going on with the ignition system-- either being caused or exacerbated by the aftermarket component, HT coil breaking down, pick up going bad, feed coil on the fritz, bad ground.

there exists an element that it may be fuel related or some type of mechanical malady: valves out of whack, clogged exhaust, carb not right, etc

but right now, all signs point to the CDI

My external rpm reader that wraps a wire around the spark plug wire is set to 1 spark per 2 revolutions and gives an approximately correct reading. But maybe OP's 2003 is different.

Do the turn signals work?

Is that on a carb'd Leader engine? Or on your fuel injected 2022 Primavera? The LT gets a timing pulse from the stator every revolution, and the CDI fires the spark plug. Very simple electronics.

See: Nexus 250 gremlins (Post 2622559)

On my fuel injected 2022 Primavera

So irrelevant to this situation with an entirely different engine...