My friend Andy had told me about this a couple of weeks back and came round on wednesday to make me a deal. His girlfriend had her old bike in a lock-up they were going to have to stop renting soon, and since it wouldn’t start, likely due to a carb problem, they’d let me have it dirt cheap and on a “pay whenever” basis.

Checked with mum since it’d have to be stored on the property and she lept at the chance to help me out, so bought it herself. That way it can go on her insurance. Very handy, though admittedly this has put me in a position I never wanted to be in again; with a non-running vehicle project and no licence to drive it. But hey, I’ve been assured it should be a simple fix and I wouldn’t be going for the CBT until summer anyway most likely.

Now the bike itself is a 1999 Piaggio Vespa ET4, 125cc.

I know a few of you are bikers and at least one is a former ET4 owner. So you may be able to skip ahead if I say “ET4, turns over, no spark after battery’s ran down”.

The bike’s cosmetically a bit messy. Couple of panels are missing and the rear box mount is snapped. But the brakes were serviced before storage and it got new tires and coil.

Here’s a picture of it after a couple of days fishing for the problem;

Mechanically everything’s sound. The model however turns out to have an immobiliser, which has reset after the battery being discharged so long. And it does not have the infamous Red Key, since it was bough as an ex-trade-in from a dealership. No Red Key means the immobiliser stays locked down. The other keys need to get the “OK” from that key once it’s in.

A new immobiliser means a new set of keys and lock barrels too.

As far as I can gather this situation is the biggest of the big red warning flags for buying a 2nd hand Vespa. It may be cheap, but getting it running will cost you £150 upward on top of it.

It’s annoying that it works aside from what is basically a software problem.

There’s two choices now, since buying the new immobiliser set is well out of my price range atm (the “pay whenever” scheme was much needed).

1. Change the CDI unit for one from another model without an immobiliser. There are several options, and aftermarket ones seem about £20-30. Looses immobiliser use entirely.
2. Find someone with a working ET4, connect laptop to serial data line and copy the “OK to go” code to a microcontroller.

The latter seems too simplistic, but the immobiliser connects to the CDI via a single 5v serial wire. Using chassis as ground, 1-wire communications seem unlikely due to noise potential, so it looks like it’s a one-way operation. The CDI just sits and waits for the go-code. And since the CDI is interchangeable independent from the immobiliser (it’s not changed as part of the immobiliser kits) it must be waiting for a series-standard code. All it should need is a copy of that code and it’ll assume the immobiliser is present.

And of course doing so would mean I could build an immobiliser system of my own later on (keypad in the glove box maybe?)

But it does mean finding someone else with an ET4 who I can plug into. Should just mean lifting out the bucket under the seat and unplugging one cable.