C72 from France

[Geoff Hastings]

You can disassemble the bottom end of the engine without disturbing the top end. Just remove the outer cases and clutch etc then flip it upside down and remove the lower case.

[sky.fred]

Thanks for the confirmation, because that's how I intend to proceed.

What type of carburettor gasket do you use?
(number 12 on the picture below)
Those sold in aftermarket are from 125 cbs or 750 Four which are not exactly the same shape and it was leaking.
I made some to measure with cardboard and gasket paste.

[sky.fred]

First long ride with the C72.
400 km of small country roads in three days with a dozen bikes from the 30s to the 70s (BSA, Terrot, Nimbus, AJS, Motobecane etc...).
Lovely outing along the Dordogne and Vezere valleys, through forests and between medieval castles.
No worries, no breakdowns, no oil consumption.
I quickly got used to the "upside down" gear selection, but putting the original mechanism back on will be more pleasant.
As I couldn't find a 250 sprocket, I put a 305 one in, and it really pulls too long in 4th gear, which is not very usable when climbing.
THe gearbox is badly stepped, with a first gear that's too short and a huge gap between 3rd and 4th.

[sky.fred]

As I fitted Fournales shock absorbers 3 cm longer than the original ones, the side stand was too short and the bike too lean. In an emergency, I made a shim. As I didn't want to modify the original stand, I adapted a “Chinese” stand.
With these shock absorbers, roadholding is good, even though we drove on small country roads with lots of holes and bumps.



Next work: Fitting the selection drum I received to get the gears back “in the right direction” and probably fitting a 305 cylinder to gain a bit of torque as the 250 struggles a bit when climbing....

The C72 with its cousins, a '72 Honda 125cbs and a '77 1000 GL.

[sky.fred]

I'm continuing my discovery of the C72 and my attempts to improve it for trouble-free use.
During the ride, with the revised electrical circuit and a modern regulator rectifier, I had no trouble keeping the battery charged while driving with the headlights off. But with the headlights on, the alternator doesn't have enough power and the battery discharges.
So I put in led bulbs .... and if that's not enough, I'm going to pool the day and night charging circuits (pink and yellow alternator wires).

[sky.fred]

Test not 100% convincing.

Although the LED bulb reduces battery discharge, it doesn't seem to be enough over the long term, given the alternator's weakness.

So I used another method. I connect the two charging circuits on a single one (yellow and pink wires on the yellow one only) and with a modern regulator, I get a little more than 14 v on charge, which should solve the problem. On the other hand, this should only be done with a modern rectifier regulator, as the original system only had a rectifier and no regulator, in which case the battery would overcharge and overheat, as I measured over 16 v without a regulator.

[Geoff Hastings]

I had no problem with the charging circuit on my CA77 but I didn’t often ride with the lights on continuously. It looks like you’ve had a nice ride with your friends through the beautiful French countryside. The Honda is a very relaxing bike to ride as long as you don’t try race it.