It depends on the type of pump but I don’t use a cut-off valve with the CB rotary pump – or a pressure regulator.
Yup. Going this route. The cutoff is to prevent petrol from siphoning into the crankcase. Belt and braces. It's also got a manual lever on it, so it's an extra little security device when parked up.
As I'm an anorak-wearing saddo, and Have No Life Or Friends...I found this on't web. It's for the Porsche 433 906 059 relay, but the KAE 3.300.300 relay Mark found is (hopefully) an equivalent. The relay part appears to be driven by a 555 (yaaay!) working as a monostable, retriggered by negative-going pulses from the ignition. With the timing component values they've got, should give an initial priming pulse of about 1s. If you were handy with a soldering iron, you could actually change this to whatever you liked by swapping out the timing capacitor Definitely warming to this. Much as I love my Pierburg mech pump, having to crank the starter for a full minute if I've left the van for a couple of weeks is becoming a bit wearysome... <edit> Probably best to put the relay in the engine compartment and pick off the "30" supply from the starter solenoid via a fuse. Don't want to hang too much on the ignition supply.
So it allows only one second for priming? That's surely never enough to fill two IDF40 float chambers? I was hoping these relays allowed a good few seconds for priming. Pretty sure the buggy takes about 5 secs with the same carbs - I've currently got that one running with an ignition live feed to the pump without a relay,
In theory - I'll find out when I get one on Friday. But as above, you could change it...to several days, if necessary . I reckon my Dells would be much the same as your Webers to re-fill the hoses, top up the Malpassi then fill both float chambers. Although the Malpassi would go.
I was going down the fuel pump relay route until I realised you only get a 1-2 second pulse to prime. As Westy77 mentioned it switches on again when cranking via the -ve pulse from the distributor. The plus side however is it’s a neat installation. As Snotty says you can swap the capacitor in the relay if your handy with a soldering iron. Or tag one of these on to give you a longer priming time.
Looking at AES website I found a bunch of timer relays - is "87a" the same as "1". They have various set time delay relays and a variable one too: https://www.autoelectricsupplies.co.uk/product/846/category/210
Your carbs shouldn’t be draining, mines been park up a year it still has fuel in the carbs and started almost straight away.
I can leave mine (with twin 40 IDFs) for a week or so and it’ll start first turn of the key or sometimes second time with just a squirt from the throttle pump. I don’t have a pressure regulator and with the filter and pump on the chassis rail most of the fuel lines remain full gravity fed from the tank and it doesn’t take long for a rotary pump to fill the float chambers – assuming they’re empty.
I have the fuel pump relay on the bulkhead next to the voltage regulator, fed from the starter solenoid.
and this is the variable version - anyone know if it would work? https://www.autoelectricsupplies.co.uk/product/1146/category/210
No. 87a is just the normally closed relay contact. There’s no provision for retriggering it once the engine’s started, so it’ll...stop.
They will work in conjunction with a fuel pump relay to give you the extra prime time. A bit pricey though compared with the one i used. Remember it’s only to give you a bit of extra priming time so if it should fail the pump will still run once you start cranking.
That's the one (maybe ). If you're doing that, see if there's any Europarts discount codes floating around...
Our usual smut aside , what I meant is: if the pump isn't powered, does it effectively stop the flow of fuel, even with the head of pressure from the tank behind it?
I’ve not checked but the carbs don’t overflow and I don’t get fuel in the oil. However, the float chambers seem to be full on the rare occasions I remove the lid so maybe fuel does pass through the pump. I’ll pull the hose off one of the carbs and see what happens but it’s a bit parky here just now so it might be a few days.
