Not charging?

[masonmart]

I've upgraded my CB77 over the years to include a Boyer power pack and a German electronic ignition system. It's been just perfect for a long time but it's now started to cut out after maybe 8 miles from being started on a charged battery. When it stops it seems to be that there is no spark but when charged it starts and runs well until stopping again. The fuel is clean and seems to be getting to the carbs freely. Unfortunately I'm not electrically competent but what I believe that it could be is that the charging system isn't working and when the voltage reduces below a certain level, the electronic ignition stops functioning as it needs a minimum V. Using a meter I can see 13.5V at the battery when charged and 12.4 V when initially running. This may show my initial guess to be right but I don't know. Question is, what is the likely fault knowing the bike? I can see perhaps the battery, rectifier and the power pack but apart from the battery, I have no idea how to check these parts. Can anybody help me confirm my diagnosis and on how I can check the charging system. Many thanks if anybody can help.

[masonmart]

My apologies. The BB power pack is the replacement R/R. The existing rectifier unit is till in place but disconnected.

[barnbiketom]

Hook up a voltmeter and see what it does after 8 miles??

[Geoff Hastings]

A simple check is to see if the headlight varies in brightness as you rev it up. If it does, you know the charging system is working but, from the symptoms you describe it does sound like the battery is discharging. If you put a meter across the battery terminals you should see about 14 volts at a fast tick over. The rectifier is a prime culprit, you can do an ohms check between terminals, should read open circuit in one direction and not open in the other. Measuring the alternator wiring is a bit more difficult in as much as it can read ok in a continuity test but it can mean the windings are short.Obviously, before you get too far into it, check the earth is clean and tight, then the wiring connections.

[masonmart]

Thank you for the responses. I think that I've found the problem, I cleaned and re-tightened the earth connection from the BB Power pack and it runs well again. Had a good little ride for half an hour with no problems at all and lights seem powerful and battery voltage good.