Hey boys and girls, I've just bought myself a 1970 beetle with an 1835 cc with dual kadrons. I've been driving it for about three days now, and in the last trip
it seemed to backfire and carry on a little bit. I don't know enough about flat fours yet to make a diagnosis, but I was wondering if anyone has any ideas? Could e a simple fix I hope? Could the spark plugs need cleaning?

Cheers.
Ollie

treat it like any conventional combustion engine. The concept is the same, but the geometry is different (obviously :P)

backfire under load? off load? all the time? warm or cold?

somethings causing it to spark when the valves are open. ignitiion timing perhaps? coudnt be valve timing as the cam is fixed inside.

Is it very gutless? run on all cylinders? Does it miss?

What sort of exhast is it? Does it run rich? Was it under deceleration? My mates 1776 with kadrons and thunderbird backfires under heavy deceleration - like down a large hill.

It happened under hard acceleration in low revs usually in second gear. Never off load, only with the foot down. As for the exhaust, it's a a twin dumpy - one hotdog one muffler i think...

I called the previous owner yesterday after it got worse and he told me I was driving it too slow! He suggested a few burns up and down a quiet street to burn off the excess petrol lying in the carbies and manifold - it did the trick!

if it doesn't suit your driving style, take it to a local vw specialist and get them to tune it up for you... its got a 110 cam... its designed to be given a bit!

Check that the exhaust isn't lose - either at the heads or the muffler itself.

Im Having the same issue with my 1970 bug. It backfires and shuts down alot. Mine happens when i take the foot of the excelorator comming down the hill at home and when i put my foot on the break at around 70. Ive tried taking it for a quick hard spin like OMClarke has done but still no luck. Exhaust is all good. Anything else it could be?