C72 from France

[deuce_7]

... But above all, the fuel tap is a real fountain leaking everywhere.

Often a tank fuel leak can be traced to loose, corroded or compromised petcock mounting screws and fiber packing seal washers, instead of a faulty petcock assembly.

See: https://www.ebay.com/itm/115052664546

[sky.fred]

The leak is coming from the internal seals of the mechanism and not from the connection with the tank.
I ordered a "Chinese" adapter because the original petcock seemed extraordinarily complex and I doubted its long-term reliability with non-oem repair kits

I also realized that all the M5 screws are 0.90 pitch (pre 67 JIS), whereas the current standard is now M5 / 0.80.
M5 / 0.90 are nowhere to be found in France. I had to order from the UK.
Ordering from the USA is very expensive for me because of shipping costs and taxes...... even though we now also have taxes for UK purchases since brexit.
The tank screws are M5 x 25 / 0,90, even though they are listed as M6 in the technical review.

[deuce_7]

... I also realized that all the M5 screws are 0.90 pitch (pre 67 JIS), whereas the current standard is now M5 / 0.80.
M5 / 0.90 are nowhere to be found in France. I had to order from the UK.
Ordering from the USA is very expensive for me because of shipping costs and taxes...... even though we now also have taxes for UK purchases since brexit.
The tank screws are M5 x 25 / 0,90, even though they are listed as M6 in the technical review.

Q: Were the three screws provided with the Chinese kit the correct M5x25 / 0.90 size?

Let us know how the new petcock assembly works out.

[sky.fred]

I received the petcock
To sum up in a few words: It's Chinese.... so approximate manufacture
Not exceptional quality, full of flaws and you have to make modifications to install it but in the end, it works.
First of all, the screws are not 0.9 but but the opposite would have surprised me.
Secondly, the O-rings on the screws are unusable because they crush and deform, so you have to reuse the original seals.
Finally, I had to modify the tap thread because it jammed in the middle of the screwing process (see photo, impossible to screw further). The female thread is M17 at 1.5 pitch, which seems OK, it's the petcock thread that's badly machined.
To be on the safe side, I've applied sealing compound and left it to dry for 24 hours, hoping it won't leak tomorrow when I put the petrol in..

[sky.fred]

The petcock, once modified, worked and didn't leak,



so I went for my first ride and the bike started up very well, the engine running impeccably.
But ....... I'm in for a huge surprise !!!!
I put the first gear down, then the second up, as with all Japanese bikes, and found myself in 4th gear.
The gearbox on my C72 is strange: I'm in neutral, then when I press the selector, I'm in 1. Normal up to that point, but to get into 2, 3 and 4, I have to press the selector again.
And that's not all! If I press again, I end up in neutral and so on, indefinitely.
So I have N1234N1234N1234 etc... but downshifting, just like on an English bike.
The gears shift smoothly, without cracking or skipping, but it does require concentration. I wonder where this set-up comes from and how it's possible?
My bike being a bitza of different models, won't I have a gearbox of an older model with the gears reversed like on English bikes?

Continuation of my investigation....

The selector drum mounted on my bike is a 24301-259-000. It's a C71 drum (for the record, CMSNL lists it as being for C72/77 and 78, which is incorrect).



The C72/C77 drum is the one below, 24301-268-000.



I'll have to open the engine, but until then I'll have to find that drum. In the meantime, I think I'll grind the 5th pin that shifts from 4 to N. That'll let me drive, with a reverse gearbox and neutral up, but without the risk of shifting to neutral if I count the gears wrong.

I also need to take care of the front brake, which is stuck in the "licking" position, and I find the clutch lever very, very hard. In comparison, the one on my Guzzi is like in butter.

[Michael Stoic]

Excellent set of reports! So much work done - I admire your perseverance! Looks to me like the bike is in the right hands!

--
Michael

[sky.fred]

Thank you very much
I found a new C72 drum in Germany and now I need to find ..... the courage to disassemble the motor and reassemble it!
I also need the special crankshaft end nut locking tool. To disassemble my other Honda, I have several of these tools .... but not the right size ! Gr....... !
I've got a three-day vintage bike tour in the Dordogne (south-west France) in about ten days' time. I'm going to ride like this and I'll consider disassembling on the way back, that way I'll have tested the bike longer and I'll see if further work is needed. I hope I won't break down during this trip, but I'm pretty serene.
I think it's possible to replace the drum without disassembling the upper engine, just by putting the engine head down and disassembling the under crankcase.
I'll take some pictures ... in a few weeks or months.