Early glass dome fuel pump running pressure

[Gary Byrne]

Do early Amazon glass dome fuel pumps have a higher running pressure than later all metal ones? I've just fitted a pair of SU's to my son's 1964 121 which has the glass domed early fuel pump and previously ran a single Zenith carb. It started and ran perfectly. With the twin SU's now fitted the car starts and seems to run pretty well but both float bowl overflow pipes have fuel running out. I don't know how common twin overflow outlets are, but anyway, I've checked the float levels and replaced the newly fitted float needle valves with the good originals but it still overflows from both carbs. I suspect excess fuel pressure and wonder if an inline fuel pressure regulator may cure the problem? Any thoughts guys?

[tdz840]

Hi
Ive run the glass dome pump for years with SUs and recently with twin 45 side drafts. Proved more than adequate but top end with the side drafts runs out of volume flow.
Should be more than adequate with the SUs.
I presume you have checked each float level is correct to spec?
Do you have the correct float valve with a spacer shim?
The float valve can be obtained with a viton tip, apparently better and can be obtained from Burlen in Salisbury.
Its pressure that causes these leaks and the pump is a fixed pressure pump. Any issues at the pump can only be less than specified pressure. The pump cant deliver more than spec.
So its float level, float valve or shimming.
I would also check the float isnt holed and effectively dropping causing the fuel to displace. However for both to be affected would be unusual.
Russ

[Gary Byrne]

Thanks for the tips. I have fitted a refresh kit bought from Burlen which did include new needle valves though I'm not sure what you mean by 'spacer shim'? If that's a shim that fits under the needle valve body then I don't have that. What is the function of the shim? I submerged both floats in water and they're both fine too. Re the glass domed pump's actual pressure I was simply wondering if it was a higher pressure pump then the more common all metal one. Obviously not.

[123GT-AMAZON]

Hi ya Gary ,

At the fuel pump where it's mounted on the side of the engine does it have a backerlite thick shim ? If not fit one that will cure your issue all being well buddy that shim will reduce the pump pressure going to the Su carbs naturally if all is ok at the su's I would check for that shim .



If the shim is in place I would then check the flow on both carbs are balanced and work on mixture and maybe pop it when not leaking on a emmison meter to see what it's doing to get the best optimum fuel setup see how you get on but keep us updated

Kind regards

Robert.w

[Gary Byrne]

Thanks Robert. I'll check that tomorrow morning.

[pookie]

I think th e first thing to do is to measure the fuel pressure.

Salut!

Pookie

[Derek UK]

In the pump are 2 one way valves. One works one way and one the other. The one on the inlet opens when needed to allow the diaphragm to suck petrol from the tank. The outlet one reacts to back pressure caused by the needle valves in the carbs when they are closed by the floats. This stops the supply from the pump. If the outlet valve isn't sealing properly under those conditions, extra fuel will carry on being pumped to the carbs and can cause the needle valves to leak.
There isn't a washer under the needle housing it is metal to metal. However some people do add a fibre one here to slightly lower the float level due to the later ones and the "no-sink" types being non adjustable. Perhaps try this.
On the early glass top pumps for the B16 which have the very handy hand primer lever the valves, from memory, were held in place by a small U shaped clamp and screw but the later ones just had the valves held in place by two or three peenings done with a small punch. Valves can loosen on these and obviously if you replace them the peening has to be done with care.

[tdz840]

The shim under the needle/float valve effectivley lowers the float height. Not sire what the thickness is but the book of specs/others may help.
Russ

[pookie]

What is the fuel pressure. If it is excessive then you have an idea of which way to go. If it isn't then there is a different way to go. Properly analyse the fault first.

Salut!

Pookie

[Derek UK]

Originally Posted by tdz840

The shim under the needle/float valve effectivley lowers the float height. Not sire what the thickness is but the book of specs/others may help.
Russ

See my paragraph in the post above. No washer/spacer is listed in the Burlen parts book.
Volvo spec for the fuel pump is 1.5 to 2.5psi. SU's should be able to cope with another 1psi on top of that without any problems. Way back there were some QH pumps which were said to put out 5psi and these did cause problems to some people but not all.
Adding a couple of extra gaskets each side of the insulator plate might help but the difference would be small I think.