Ducati Sporting Club UK > DesmoDue Race Series > DesmoDue - General Questions and Chat > Lack of petrol flowing

[antonye]

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.

[ells]

Cap ordered!
Couple of fuel filters ordered.

Just hope it all works

[bradders]

have you got a non return valve on the outlet Mark? I think Skids fitted one to Craigs bike last year so no need for a catch tank

[ells]

Originally Posted by bradders

have you got a non return valve on the outlet Mark? I think Skids fitted one to Craigs bike last year so no need for a catch tank

1. Not sure where the outlet is!

I cant see a valve so I am sure there must be some need for this. I was assuming one of the two outlets at the back of the tank were something like this. Might try turning the tank around a few angles to see it owt leeks and then figure if it leeks it needs something.
Cheers
Mark

[bradders]

From memory its out the back of the tank at the bottom near the fuel filter, one long pipe which goes down thru the frame towards the bellypan

[skidlids]

Mark I thought I would put my answer to your PM here as others may want to comment or take note

"Yes the Breather comes through from the underside of the tank, the other is the drain to stop rain water building up and then getting into your fuel every time you open the cap

On the underside of the tank on my 750 Monster they are marked Bleed and Drainage respectively
These can block up and I have had to use welding wire to clean them out before
The Drain is outside of the fuel cap seal so under normal circumstances shouldn't see petrol other than when over filling or being a bit sloppy when filling . The bleed should come up to a small rubber grommet like thingy that lines up with the breather in the standard filler cap which should contain a one way valve so no catch bottle needed

Most cheap Aftermarket filler caps fitted to Ducatis are actually Yamaha ones and the breather is in the wrong place to align with the bleed on the Ducati tank.

[ells]

New fuel cap on. Countersunk bolts on order. The new cap mechanism needs countersunk, where as the old one did not. Try getting bolts on a Saturday!

All on and good flow with a new fuel filter added as I cut the last one open to have a look see.

Have revelaed most of the frame number, enough to see it hsa not been tampered with. Hope thats sufficient. I am afraid to rub much more it looks like it could be rubbed away.

Many Thanks folks