Iso Moto 125B – Introduction

The manufacturer of the original Isetta Bubblecar also made a series of scooters and motorcycles.

Mine is the Iso 125B, with a 125cc split single engine, giving a whopping 6.5 H.P. It has a single 18mm dellorto carburettor, and a three speed gearbox driven by a chain primary drive. “Lighting” (I use the term loosely) is provided by a magneto, with no battery. Stopping power is supposed to be provided by SLS drum brakes front and rear, with 14″ wheels to add to the fun of finding tyres. I bought it on that well known auction site – it was a non-runner, but it wasnt seized, and that was all I was really worried about.

As and when I get round to it, I will be uploading photos and text explaining the rebuild – a bit of a detailed project blog. Below is a summary of what I’ve done to date, and what’s in the pipeline. If you click on the headings you should get to see the gorey details.

The idea is to pass on what I’ve learnt – it might be an interesting read if you’re really bored, or it might even help to prevent you making the same mistakes as me, should you be rebuilding your own Iso. If the latter applies, you’ve already made one mistake by buying the thing – now it’s just damage limitation. I jest – the Iso has been, and continues to be, a rewarding and enjoyable project. It’s a popular bike at shows, so will be worthwhile at the end

The information here is provided in good faith, and I cannot accept liability if you screw up whilst, or as a result of, following what’s on here. As far as I know, there are no Iso workshop manuals available, so please use common sense if you think I’ve done a bolt up too tight, or if I’ve shown something assembled incorrectly. My approach has been put it back together the same way it comes apart. I do not claim to be an expert.

Part 1

Upon delivery, I made a very quick list of what needed doing, based on appearances alone and an initial attempt to start it. Effectively, this was “phase 1“, of the never-ending saga that is my attempt to recomission a bike, but not restore it.

Get it to run – there was no spark, the tank needed cleaning but at least it had no holes

Electrics – Italian electrics have a bad reputation, but, despite the fact almost every bit of wire has eventually been replaced, fixing the electrics was probably the most rewarding bit!

Sort out cycle parts – The old tyres had to go as they werent round. It needed new shock absorber bushes, a fork gaitor and a few cables. Brakes were shocking, too.

Register it – it had no logbook or plate, but it did have a NOVA certificate. I needed an age related plate, and was reluctant to go further with the re-build until I had a logbook. As a “young rider” (under 25, though they keep moving the goalposts) a Q plate and the subsequent insurance price hike would’ve stopped the whole project

Part 2

Having completed the above , I though that I could now ride the bike with reasonable reliability and legality. I think I completed about 2 journeys – the worst being an 8 mile trip, in which I broke down several times. The replacement engine didnt help either, as it was just as worn out. Bulbs kept blowing, the carb kept overheating. It was not a fun experience

So it was clear a lot more work was required . Work done to date includes –

Engine re-fresh, including new pistons and bearings. Not a full rebuild, as the big-end bearing was OK. Repair broken kickstart. I’m still trying to bed it in, as it siezed on the first run.

Electrics – the sequel Rewired magneto stator, new 6v regulator, LED and halogen bulbs, to bring it into this century

New centre stand – the old centre stand broke so a new one was made from CDS steel tube. It wont break again

Cooling. The warm carb problem has been solved by removing the legshields, only temporarily

And there’s plenty more – as of June 2020 I’ve also got the following on the to-do list

Brakes – get the shoes relined

Fuel tank – sort the fuel taps out, as the crank fills up over time

Cycle parts Turns out the swing arm bush is now worn out, as are the front forks.