Honda C90 ZZ 1981 6v won't rev

[joefish]

how old is the battery

[cpradel13]

Loadedtoad,

Unfortunately, I don't think is that, I check inside the tank it and the metal tubes look clean (which it doesn't mean much, but looks ok) I took the part of the carb where the fuel pipes go and the flow is really good (like a little boy doing a number 1...)

Joefish,

I am not sure how old is the battery, we did put it on a slow charge for 24 hours as well just in case, trying to eliminate battery issue and it looks like is holding the charge well.

What about CDI or ignition coil? could this be the problem?

[joefish]

it sounds to me like the battery is on its way out its just enough power to start the bike but when you put a load on it its not up to it
the battery on the zz models have to be in tiptop condition to run the bike, i usually get about two years out of a battery on a zz
ive had the same problem in the past when the battery is on its way out the bike starts to bog down then its time for a new battery

[cpradel13]

It may not be a bad idea Joefish, a new battery won't hurt at all and worth to try.

[damien.wrl]

Far from an expert and I know you have the main jet clip in the middle but maybe it needs to drop down a bit. Sounds like the carb not transitioning from idle to main jet ? Had this problem on mine

[loadedtoad]

Following up on Joefish's suggestion bad battery lack of spark.
Have you or your helpful neighbour got a timing strobe
Attach it to the bike and see if the engine is till sparking consistently when it bogs down.
Might be the condenser or even plug cap it's caught me out before in my early years.

Nowadays I attach a digital oscilloscope with inductive HT clamp at this point to see what's going on.
But appreciate it's not in most peoples tool boxes.
Ten minutes with the right tool can save days/weeks off messing about !.

[cpradel13]

Thank you Damien!!!
I'll play around with the jet clip and see what happens.

Loadedtoad,
WOW I love the technicality, I'll send your message to my neighbour, I am sure he will understand and if he doesn't have the tools, you have giving me a great idea to get it for him as a present, for his kindness

Happy new years guys!!!! I am sure we will make the C90 running on its 40th!!!

[125erCrazy]

Late to the party but replace spark plug.

[loadedtoad]

WOW I love the technicality, I'll send your message to my neighbour, I am sure he will understand and if he doesn't have the tools, you have giving me a great idea to get it for him as a present, for his kindness

He would love that i expect, my scope cost about £1200 quid 8 years ago.
But if he's technically inclined probably already has something usable to hand.
If he's not familiar with HT spark scope traces there's plenty of info online.
It will be something simple it always is it's just finding it

[cpradel13]

Never too late 125erCrazy, I have two spark plugs (one it's new) and same thing happens with both

The current battery is Yuasa 6N5.5-1D. Is this the correct battery for the C90ZZ 1981? (for what I have seen it looks right).

I think I am going to get a new one. I don't really know how old it is and I just tested again and it is 6.14v (which I think is a bit low...).

Thank you guys, what an awesome community this is