Carburation

peterg · #1 (**permalink**) 16-09-13, 09:49 PM

Thanks Jeff,
The pump was fully checked over when the engine was rebuilt but I pulled it apart when trying to trace a fuel starvation problem (traced to a fractured ferrule in front of the pump).

As said I have had the engine running for prolonged periods before risking it on the road. The pump has to be primed after a few days of non use before the engine will start.

Never too lazy to open the bonnet. Possible that is my problem!

Regards, Peter

Geoff Dowdle · #2 (**permalink**) 17-09-13, 12:19 AM

peterg,

When you had the pump apart did you remove the top casting to expose the diaphragm ??
When re assembling it is important to hold the priming lever in a position to pull the diaphragm down from its central/natural position , otherwise the tension on the diaphragm will be too great to allow it to work correctly at higher revs.

I bought a simple pressure gauge and adapted it to a spare banjo bolt to check the running pressure of the AC pumps when using Solex carbs. From memory pressure should be about 2.5 - 3.0 psi . I once had a problem with a engine lacking fuel under load , at idle and cruising it pumped about 2.5 psi but once under load going up a steep long hill the pressure dropped away to about 1 psi.

Having to prime the carbs after a few days of not running is common,
it is often caused by the emulsion tube holders being loose in the carby body (originally a press fit , but I carefully remove them and Loctite them in , to seal them) , where they enter the body is below the fuel level so over time the fuel in the bowl leaks out through the carby throat into the engine .
Over a longer time fuel evapouration occurs to what fuel is left.

Geoff

peterg · #3 (**permalink**) 25-09-13, 12:28 PM

Not sure what you meant by holding the priming lever in position Geoff as the position of the diaphragm in relation to the operating lever is fixed.

Replaced a valve that didn't appear to be working and refitted. The car started in a cloud of smoke and settled down. But after about 5 minutes of driving around, just as I was about to back it into the garage it cut out and once again would only restart if on full choke and primed. Then in runs for about 8 seconds and cuts out.

I am beginning to wonder whether the diaphragm spade is locating securely in the operating arm as the petrol level is only at the level of the gauze filter. Is this a common point of wear in AC pumps?

peterg · #4 (**permalink**) 26-09-13, 10:06 AM

Latest progress. Checked the pump and the diaphragm spade is still locating securely in the operating arm but after use the petrol level is only half way up the glass bowl.

Will replace the petrol filter and check the flexible line. Not much else I can think of.

flyinghorse1 · #5 (**permalink**) 26-09-13, 09:32 PM

The diaphragm can be attacked by ethanol & perish--is it intact? You would soon know as petrol would enter the oil system & oil pressure would drop.
You can get ethanol proof ones now.

I had problems getting a good idle and I eventually made new gaskets for the stubs that the solexes mount onto the head,using hylomar on all joints and surgically rebuilding my carbs.

I cant fully recall but the float needle valves may be worn /sticky. I got new rebuild kits from gower & lee.

Note the only level setting is by means of varying the packing washers under the Needle Valve and as Geoff says the 16mm is critical.

I also found that a leaking water pump meant erratic firing on front cylinders,and I had 2 duff plugs as well.

peterg · #6 (**permalink**) 27-09-13, 05:50 PM

No the diaphragms are good.

I did change the fuel filter today as it had some crud in it. No improvement.
Final check. Undid the union, turned the fuel tap on. Nothing. As the fuel gauge reads half full and is probably correct the fuel fuel line is blocked.

Makes sense. But how to clear it? It's a long way from the fuel tank to the isolation tap.

flyinghorse1 · #7 (**permalink**) 27-09-13, 08:59 PM

Peter,
You really have to drop the tank & sort out why crap is getting through.

I have had this as a student in a Hillman hunter and used to carry a foot pump to pump the crap back to the tank from the engine side . However it always returned.

I also have a vintage Swift that did this-and cut out like you said. The motion must be mobilizing fines & clogging the line.

You may get lucky by draining the tank & starting afresh.

Frost do a slosh kit that should fix the issue if you get the tank out--I have used it in my Swift & a friend in an AC Ace and it works.

POR-15 Car Tank Repair Kit | Frost Auto Restoration Techniques

Graham