A friend sent me a post he'd read last night. It said: "As in a bus the fuel tank is mounted higher than the carbs, this can cause siphoning if the vehicle is left on a slope or unused for some time, and the fuel can run through the engine into the sump!!! This seems to happen if you have Dellorto carbs and have an electric fuel pump. The post I saw last night seemed to explain why this didn't happen as standard; It appears that the vw pump had some sort of diaphragm valve built into it to stop this from happening." I'm fitting IDF40s and a Carter rotary pump. Should I be worried? Has anyone else heard of this?
I have no experience of Dells or any other non-stock carbs, but the best safeguard regardless of the delivery system is to plumb in a fuel shut-off solenoid valve and wire it through the ignition. As well as stopping the siphoning you described, this would also stop fuel gravity feeding a fire and give you half a chance of extinguishing it.
Carbs have a needle valve in the top that shut off fuel flow when the carbs are full. They will only leak if they are worn, or stuck open due to crap in the valve. That said, adding a shut off solenoid won't hurt if you want to add a secondary safe guard.
But the fuel does evaporate from the carbs as they are vented to atmosphere and would still be toped up from the tank.
I fitted one on mine, just a cheap thing off eBay, works fine and i hooked it up to the fire extinguisher so if that is triggered it shuts.
As dubs says if the float valves are set correctly and not worn or stuck open with crud then you won’t have this problem
I had a problem with syphoning. I have 34 icts and a stock pump ( and a sloped driveway). Needle valves were new, and I had a fuel pressure regulator. I ended up fitting a solenoid valve wired to the ignition which cured the problem. Just a cheapie off eBay. US Solid I think the make is. Been in a couple of years with no issues. Sent from my Nexus 5 using Tapatalk
Thanks everybody. Belt and braces it is then. I'm a way off fitting stage yet but I'll definitely fit one.
But if the solenoid on the carb is OK then evaporation is going to be negligible as no displacement air will be admitted. That's on stock carbs. But if you don't have this, for peace of mind I'd fit a fuel cut off.
No solenoid on Webers, so just in case 3 bar of fuel pressure from my electric pump is enough to force open my needle valves (new) I'll fit a solenoid valve to cover my arse.
If you put 3bar on Webbers icts you will blow the float needles. Nothing wrong with stopping fuel disappearing my filter king drops its level if I don't use my van for a long time.
That's the recommended pressure for IDF 40s I believe and it's what the Carter pump puts out as standard so no need to use a regulator.
3 bar is a lot? If your pump is putting out more pressure than the carbs are designed for then it will overcome your float valve when the engine is running and you will be running rich and causing bore wash.
All of the above. Even 3psi might be too much for your float chamber valves. Fitting a pressure regulator like a Petrol King might be a good idea with an electric pump.
I had the siphoning petrol issue about 2 years ago, sourced a good refurbed solex 34 pict3 and installed a 6mm on the manual motor bike in line petrol tap just inside the engine bay on the left side so I can switch it on and off easily. lots of the metal fuel taps on ebay and cheap. Its an option.
