Lancia Motor Club

Model Technical and Interest => Aurelia => Topic started by: Dikappa on 04 June, 2017, 04:46:30 PM

Title: carb overflowing
Post by: Dikappa on 04 June, 2017, 04:46:30 PM
Today all seemed well.  The carb seemed not to be dripping anymore, so I made a short trip around the block, checked again, all OK, so made a bigger trip.  Having the window open with the good weather after a few miles smelled fuel, so pulled over and opened the bonnet.   One carb really heavily overflowing, even after stalling the engine, it seemed endless.

Any idea's?  I just opened it, and off course now all seems wel...  Checked the float in a cup off fuel to detect leakage, but I'm a bit out off idea's.

Could it be the fuel pump is just delivering too much pressure?  This because every time I diconnect the fuel line it sprays like a garden hose, which is totally unnecessary in my opinion.

Could it be a minor crack in the float opening up when warming up?

They should make plexiglass carbs so one can see what's happening!

Any input most welcome....

Title: Re: carb overflowing
Post by: frankxhv773t on 04 June, 2017, 07:19:40 PM
Forgive me if I am teaching my grandmother to suck eggs but is the float chamber inlet valve sealing when the chamber is full? if it is over pressure from the fuel pump would a pressure regulator help?

Title: Re: carb overflowing
Post by: chriswgawne on 04 June, 2017, 07:37:55 PM
If you have an electric pump you definitely need a pressure regulator in line. I have original ones if you want one.
And I would also fit a regulator/filter if you are just using a mechanical pump.
The last thing you want is petrol spraying around the engine bay. There are many stories of Aurelia engine bay fires.

Title: Re: carb overflowing
Post by: simonandjuliet on 05 June, 2017, 07:04:51 AM
I can't remember how you adjust the float level on an Aurelia, but can you lower it and ensure the valve is fully closed ? Is the float sticking in the float chamber ?

I have had both problems on Appias

Title: Re: carb overflowing
Post by: Dikappa on 05 June, 2017, 07:51:28 AM
I think Chris pointed me in the right direction.  There is a Malpassi filter/pressure regulator in the car. (thought it to be only a filter I must admit)  I suspected maybe some dirt or a malfunction, and opened it up (also because that helps me best to understand how it works)
I now understand that screwing in the screw on the top makes the internal valve open more easily.  The screw was fully turned in, alowing the fuel so simply pass the next question arises: what is the procedure for properly setting it up?
If I just blow in it, it needs very little 'screwing in' before it opens up, is this a trial and error setting?  Or should i attach 'real' air pressure and a pressure gauge to monitor the outlet?

Simon,  I checked the float to be free at the sides, but maybe need to check the float does'nt touch the back of the float chamber when lifting...yesterday I discovered that the carb's cover is slightly deformed which may have caused the support of the float to move a little backwards...that seemed to far fetched for me, but as you have encountered the float sticking will further investigate!

Title: Re: carb overflowing
Post by: Jaydub on 05 June, 2017, 08:08:40 PM
The only sure way to set the correct fuel pressure (2.0 - 2.5 psi) is with an inline gauge. You can buy a gauge 0 to 15.0 psi, with a `T`piece adaptor that the gauge screws into from
Price for the 2 items is 31.00  (35.43 euros) which is cheap compared to the cost of a fire, as Chris has mentioned. Might I also suggest new float needle valves if you`re unsure of their history.

Good Luck.

Title: Re: carb overflowing
Post by: GG on 06 June, 2017, 09:00:35 AM
Typically I've used 3PSI (I think the range is from 2.5-4psi).

I didn't use a regulator, but we checked the mech'l pump pressure over the rev range - as the electronics pump runs to the mech'l so the mech'l pump was the limiting device.  The mechanical pumps can be very erratic, especially because the ends on the rod that activates it (and goes back to the inside of the engine to activate it) wear over time. We also discovered that the mech'l pump pressure is quite sensitive to its mounting (which sets up the rod distance) and that a spacer just the thickness of a paper gasket would change the pressure a lot.

We also took apart 4 mech'l pumps to make one that was right. So yes, a pressure regulator is a good thing to have.

Along these lines, I've wondered if historically pumps have acted up, sending too much gas washing down cylinder liners. This might explain much Aurelia engine wear.

Hope you fix this in time and make the Sliding Pillar!

Title: Re: carb overflowing
Post by: Dikappa on 06 June, 2017, 10:42:29 AM
Again  I delivered proof that it's a good thing to keep all this stuff lying around that she always wants me to throw away, as everything needed to make a petrol pressure gauge was found in the basement...
I set it to 0.20 bar (2.9 PSI)  feeding it with pressurised air at 1 bar.  But maybe need to do it again on the car?

Title: Re: carb overflowing
Post by: Jaydub on 06 June, 2017, 08:03:50 PM
You need to mount the gauge between the regulator and the carburetor with your tap open to see what the pump is delivering and then set the regulator accordingly.
I have no knowledge of Aurelias but I have never seen fuel pressure to a carburetor higher than 2.5 psi. I stand corrected if someone proves me wrong.