Quote:
| Originally Posted by ells So why do I have no catch bottle for petrol overflow? Surely there must be an overflow pipe for the petrol! Theres still two pipes at the back of the monster tank, are they both overflows for the tank? Cant see a good reason for two pipes. |
On the fuel injected systems they use a pressure valve at the throttle bodies, which is set to around 3 bar, I think.
If the pressure builds up more than this, the valve opens and the fuel flows through the valve, straight back into the tank. It's effectively just pumping the fuel round in a circle, rather than into the throttle bodies. This is a closed-circuit system, hence it doesn't need an external vent/overflow. Again these are usually nothing more than something covering a hole (like a blanking plate or ball bearing) and a spring which has a specific tension, just like in the fuel cap, only they work the other way round in that the pressure is pushing against the spring (so the increased fuel pressure overcomes the force of the spring) rather than it pulling on the ball which acts against the spring.
Not sure how it works on the carby models tbh, but I'm sure that the carbs have an overflow pipe that probably vents to atmosphere by default if they do overflow. Normally the fuel would just shut off if it's a gravity-fed system because the pumps are much lower pressure.