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Discussion Starter #1
Good morning!

I have rebuilt a 79 honda barn find over the past year and took it on its maiden voyage yesterday where I began to encounter some problems. Firstly upon starting the engine seemed ok (a bit sluggish because it wasn't warmed up, fine).

Problem 1) I kicked it down into first gear and the engine ground to a halt (with the clutch in) at higher revs it seemed to be okay but at idle the engine didn't seem to like being in gear and would just die out. I think this began to remedy itself once the bike was more warmed up, the clutch cable is correctly adjusted and pulls as it should.

Problem 2) After about 2 miles of riding the bike seemed to be getting weaker and weaker, I could feel the rpm dropping dangerously low when I wasn't holding the revs deliberately high. I pulled up to the side and once my hand was off the throttle it cut out completely. I did notice that the fan was on (I replaced the mechanical one with an electrical unit, it is wired directly to the battery so it may continue cooling the system after the ignition is off - a relay was used as well). After the fan had stopped running I tried to turn the bike over.. nothing - then starter motor made a lazy turning noise then gave up, no spark, no starting... I left it for about 15-20 minutes and tried to start it up again... Boom, there was life and I managed to ride it back home (just). It sounds to me like I may have a bad rectifier OR the fan is pulling too much power

Has anyone else on the forum experienced any issues like these before?
 

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Discussion Starter #3
The carbs haven't been messed with and are stock as far as I am aware, there has been a higher air flow filter utilized but I doubt that would have done much.

I haven't conducted a stator test as such, no. Is there a way of determining if it is the stator or rectifier? (as I don't want to throw money at it unnecessarily)

Checked the fuel cap vent as per your suggestion and there is no issue there, petrol flows smoothly.
 

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The carbs haven't been messed with and are stock as far as I am aware, there has been a higher air flow filter utilized but I doubt that would have done much.

I haven't conducted a stator test as such, no. Is there a way of determining if it is the stator or rectifier? (as I don't want to throw money at it unnecessarily)

Checked the fuel cap vent as per your suggestion and there is no issue there, petrol flows smoothly.
Stator test is here:

https://motofaction.org/motorcycles/honda-cx-gl/how-to-check-test-stator-honda-cx500/

As far as the rectifier goes... your ignition system isn't 12V driven so the rectifier is unlikely to be related, unless you have replaced the CDI box with an Ignitech already. What voltage do you get across the battery terminals when off, at idle and at higher RPM?
 

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