Running aftermarket single or dual carbs on a aircooled VW flat four will probably require you to fit a fuel regulator to ensure the carb(s) receive the correct fuel pressure. Carbs don't like being force fed or starved. Bit like me really. Ok, just the second one.
I ran twin 40 DRLA's on Myrtle with the standard repo mechanical fuel pump and just a little plastic filter for about a year with no issues, but that's not to say my pump just happened to be a nice suit pressure wise for the carbs. It has be known for the standard pump to throw out 10psi. Maybe I was just very lucky. Why I didn't check the pressure is still a mystery to me, but it doesn't matter now as I have fitted a Facet Posi-Flow (Model 60106) and a Malpassi Filter King Regulator set initially 3psi.
Finding somewhere to fit the regulator in an already cramped 1200 engine bay was a head scratcher. The answer came in the form of a mistake, as the regulator arrived with an alloy bowl and not a glass one. This allowed me to mount it right where the fuel line emerges from the gearbox forks(?). Slightly bent bracket bolted through the floor of the rear seat area does make it a bit of a pain to adjust, but this is rare operation so not really an issue. A word of warning, make sure you use a decent quality pressure gauge as the crappy £4 EBay one I had lying around the garage was, er, lying. The fuel pump was mounted in the nearside triangle plate under the fuel tank with a Facet filter union on the inlet side, earthed to the chassis and the feed wire winding it's way to the loom behind the dashboard.
Previous to this we had fitted a Facet Solid State pump and Filter King to Mark's bus so knew the combo worked well. I then started thinking about relays. Knowing that running a fuel pump direct from the ignition is a second disaster waiting to make the first disaster worse, I wanted to run a relay like most normal production cars do. So I headed over to VZI to see what the wise and knowledgeable had to say. Luckily, one of the most wise and knowledgeable had posted on a thread with exactly what I was looking for, here. What I loved about this design is the bypass relay that kicks in when cranking and the alternator light is lit effectively starving the carbs of fuel if it were just a single relay design. So I grabbed a couple of 5 pin relays (You can use a 5 in place of a 4, you just don't wire up 87a) and fitted them to the bus. That all worked well.
On the bug, I used micro relays instead along with a couple of bases to ease installation. All seemed to be fine but it was an absolute pig to start after a long layoff. Obviously the fuel in the float chambers had buggered off and we were essentially priming the carbs with by cranking the motor. This wasn't an ideal situation and along with a dodgy connection was one of the reasons a Damage club beetle that we fitted this design to didn't make it to a show. (Sorry Emma ). To combat this issue I decided to revert back to Dave's (Mr Whippy) first wiring diagram and introduce the priming switch. I fitted a momentary switch, removed the second relay as if you really need the pump to work while cranking, you can hold the button down until the engine fires and the first relay kicks in.
Not really sure why Mark's bus works so well after a layoff with the dual relay system. Maybe it's to do with the very short fuel run plus the added benefit of gravity. All I know it works and if it ain't broke, don't fix it.
Below are Dave's wiring diagrams as well as a terminal mapping table if you want to use micro relays.
|Full Size Relay||Micro Relay|
Many thanks to Dave for letting me use his diagrams and for the many posts on VZI that I am sure have helped loads of people, myself obviously included.