Howdy vdubers I have a 75 1800 kombi.
In the last week or so the bus has been backfiring and running rough randomly then it comes good and runs well again.
I took it in for a service but as the backfiring in sporadic it's hard to diagnose what's going on. At first I thought carby problem I had a quick look this arvo when she was playing up nothing visual that I can find. I'm now leaning towards ignition it has a crow cam fireball xr700 electric ignition I have been told it's an unusual choice for a bus as it may not handle heat well( could be failing ) .
Can someone please help as we are traveling oz I found work but I need the bus to run smooth to get there.
Any help would be great thanks.

When is it backfiring?
On overun, accelerating, driving, hot, cold?

it may be sucking air some where on the inlet side

Check your coil or borrow one and see if that's the problem. I had similar symptoms, thinking it was the carbies or an exhaust leak, when it turned out that the coil was on the way out.

Thanks guys I dont think it would be a vacume leak as it's not idling high and a leak would prob make her cough all day long. When it's playing up it idles rough and backfires under load like a leak but then clears up but it is getting worse( longer episodes of bi- polar) Total of three times first was 5 mins today was 30 mins
I'm thinking you might be onto something shokwave2 do you know if i can I check the coil with a multimeter ?

Not sure. Maybe a veteran of this site can answer that. I just borrowed a coil, thru it in, and it ran perfectly. Before that i took my carbs off twice and my exhaust system off about three times chasing a non-existent leak

Where you at? Maybe a fellow dubber can lend you a coil to test.

Tracking in the distributor cap?

AA how would I check the distributor ? Ill have to look tomorrow loose button ? Burn marks ect I'm a bit new to workin on my bus I'm trying to get a bit of experience :-)

grab hold on the carbies up high n give them a shake that will tell if tehre loose

Also check the vacuum balance line

then go for the dissy and leads n coil

wait till night than start her up get some one to start and you watch the engine see if there is any stray sparks failing that get a squirter ottle and half fill with washing up soap and water crank her up to around 2 rpm and spray aroundthe manafods if there is a leak it will sucked in the soap bubbles make it easy to see it
good luck
steve

Have checked for leaks, checked leads, check fuel flow rate carb not loose, checked distributor button for resistance I'm loosing my mind!! Going down to buy a new coil and maybe a resistor if that dosnt fix her I think it must be the crowcam ignition system.

Ok so I havnt found the problem it's still a bit under powered and is missing slightly but the bus is running alot better.it's running a gt40r coil with a ballast resister into the elec ignition.
The dizzy is measuring 1.9 ohms disconnected and so is the resister any idea if this sounds right??????
Next step will Be removing the whole set up and going back to standard dizzy and points to eliminate another area but that won't happen till next Friday.
At the moment I am driving an hour to work so we are packing up and moving closer so I can catch the train to work. Incase the bus stops altogether. Another kombi adventure haha

Changed the coil out this morning with no effect :-(
Down to the dizzy and elec ignition

Have you checked all electrials in the engine bay. Could be a bare wire touching tinware or another wire. Or loose connection on coil/distributor. It's a pain chasing these problems.

hmm putting my bets on electric ignition

Just swapped my mates electric ignition dissy over to points and condenser, and now purring like a kitten. Mind you, it was missing and kangaroo hopping as opposed to backfire. But when i had my dissy failure it was backfiring.

The base of electronic points dissies (if bought as a whole dissy) is simply a 009 shell (if no vac advance), and a set of points and condensor just bolts in. My mate and i got this advice from Roger at south side vw, points are not as high maintenance as people say. Takes a minute to check the gap every so often, and if its drasticallly out another couple min to reset ignition timing after setting gap.

Condensor and points (in bosch german quality form) ended up only $24 ish... cheap check.

This is the set up is that vacume advance on the dizzy?

certainly is! if the advance mechanism gets jammed or the vacuum line connected/blocked, it can cause big woes too another thing to check.