misfire/overcharging?

IF switching on the lights instantly cures the misfire, if running the bike on battery only without any charging (disconnect reg/rect) cures the misfire then over volts/charging is the cause. You say you have checked the reg/rect yet you say you have 18V (primary cause reg/rect failure) ??

BUT real cause of apparent 18V liable to be cheap digital meter picking up ignition interference.

Real cause of misfire liable to be loose wire or worn carbs.

Surely 18V would blow all the bulbs?

Are you 100% sure that all the drillings in your new carbs are perfectly clear of swarf? You wouldn't be the first to find out that they weren't. Can your fuel tap flow enough fuel? (eg. is the filter on the tap blocked)

What ignition system are you running? Boyer, for example are renowned for breaking the wires INSIDE the insulation near to the engine/inside the points cover/at the back plate, i.e. from outside it all looks good, but it isn't in reality. Sometimes they touch well enough to run well, but at high revs the contact vibrates apart and you get a misfire. Running a new wire from backplate to control box to check that out is a lot cheaper than a new regulator!

Have you done what Al suggests? i.e. disconnect the alternator and reg/rec from the circuit (total loss battery) and checked whether it run ok or not? If your misfire is still there, it isn't the regulator.

Also, how old are the coils? HT leads? Plug Caps? Plugs?

If your lights are all still working, you are not getting high voltages as the bulbs won't take it, so it is probable that your reg/rec is ok

Just trying to save you the expense of a new regulator when what you have is perfectly OK

Isn't it funny, people have a problem, you give them advises and they ignore 90% of it especialy the easy to do bits. And then wander off to spend money!

You are right George, 18V would have killed the battery and blown the bulbs. By the way you do not have to disconnect Alternator and reg/rect. You just pull out one wire, the BLACK from the reg/rect (or one alt. wire).

And as we keep reminding ourselves, a missfire that is electrical will be petrol and lack of petrol is a bad connection!!

Modern digital meters have trouble reading voltages on running old bikes due to interference from the ignition. An old analogue meter does not have the issue.