Hi guys. I just got home in my GF's 1972 1600 bug in quite distressing circumstances.
The engine has been a little off lately as it has been backfiring in (or should I say outside) one cylinder when under load such as going up hill.
I wasn't sure what the cause of this was and was going to get a service in a week in school holidays (yes I'm a teacher).

Tonight after the car had been sitting for two and a half hours we got in and after some difficulty started it. There were clear problems as we could hear that two cylinders were firing, but the other two weren't and the fuel was detonating late (backfiring). It's only a ten minute drive home and we didn't want to get the car towed without giving it a chance so we saw if we could get home. Basically the situation didn't improve but we did get home on just two cylinders and alot of farting.

There are a couple of possible causes that my dad and i came up with.
The fuel filter over the last 8 months or so has indicated that we've had some bad fuel go through as it's had to be changed (brown not black residue), but it seems like fuel is getting through so:
I'd noticed that the stock oil based air filter for the carbie seems to be leaking a bit and this has had me nervous. Oily residue has been leaking directly down onto the fuel lines and landing on the distributer. This may be corroding the fuel lines, but as I said fuel doesn't seem to be the problem. It may however be causing some carbon buildup in the distributer and shorting it?
The other possibility is just that one of the clips is not properly fixed to one or two of the spark plugs?

Has anyone heard of this before or anything similar?

For these sorts of questions you are better off trying a repost in tech talk on this link more likely to get a response.Tech Talk

thanks for the redirection