Technical Differentiating engines 650 vs 500

[BambinoClassic]

Hello all,
Eyes are always out for interesting 500s in Aus and this one had me curious as to if it's possibly got an uprated 650 in it. The owner brought it out from Italy many years ago and put it in storage, but it looks like a nice specimen. He's going to chase the engine number which I assume is where I've circled, but wondering are there any clear visual identifiers that make it a 650 vs a 500? They've always looked the same to me but this one is RED! so it must go faster... :slayer:

 

[Paolo66]

650
It has an alternator not a dynamo
The air tube has that bigger diameter in the middle
The exit from the thermostat housing is different to a 500
Check on the head between no 1 spark plug and rocker cover. It should say 650 on it

 

[Paolo66]

Oh and tell him to remove that plastic fuel filter. If that melts you’ll have fuel all over the hot engine

 

[the hobbler]

At a guess, I would say that it is a 650. It has an alternator, and the intake on top of the carb looks like the ' plastic, sloping' version rather than the 'aluminium, right-angled' version as on the 500s. If it is a 500 engine, it will start with '110'---if it is a 595 (126) it will start with '126A' and if it is a 652 engine it will start with '126 A1'. The carb on the 652cc engines was a Weber 28IMB---all the earlier engines tended to have variations of the 26IMB. Hope this helps---looks like a neat conversion.

 

[BambinoClassic]

Thanks for the replies and pointers. Small (or not so small) things obvious to some but not yet me!
Seems like it’s worth a look. The 650 is a relatively rare conversion here but one I’d like, just to be able to keep up with city ?

 

[BambinoClassic]

This forum is great
After some scouring and the right keywords I came across this thread
https://www.fiatforum.com/500-classic/455808-what-have-i-got-image-heavy.html?455808=#post4308080

And based on this pic of the engine number, it does look like a 650, with the 126A1 000 stamp