Overfloating problem SU

[UHR850]

Oke, thanks.

[onetim]

I chased the same problem for 3 years with twin 1.25 SU's on a A+ 1275. It turns out the A+ mechanical fuel pump puts out 4.5 Psi, added a Holly 2.5 Psi pressure regulator, alls good.

[UHR850]

Thanks but I have stil the same problem.
Maybe I bend the metal plate on the floater a bit down so the needle will (I hope) close sooner.

[Peter Laidler]

Right......., before we go any further, let's isolate the problem. First, Does this flooding problem happen on BOTH carb float chambers or just ONE? And which side (irrelevant really but thought I'd ask. If it is BOTH bowls than that tells me that the pump pressure is too HIGH and the pressure of the pump is hydraulically overwhelming the buoyancy or ability of the float to close off the float bowl valve. This in turn back pressurises the pump so that in short, it stops pumping.

If it is ONE bowl that is overflowing then it is clearly that singlefloat and/or float bowl and\or needle valve assembly that is defective. There's no need to start bending the float bowl float lever. If it's correct, it's correct and if you start bending it........ Anyway you need a cure and not a palliative fix

On yours, because the fuel continues to flow, albeit slowly, the pump continues to pump......, once again, slowly. But it STILL pumps, the pressure of the fuel still overwhelms the float and therefore the ability of the needle valve to close, so it drains out of the vent hole.

First Q. Is it one or both carbs leaking?

[Peter Laidler]

Oooooops, duplicated and deleted

[UHR850]

Just one on the left side, there was no problem with it. It just started all of a sudden.

[Peter Laidler]

GREAT...., that is GOOD news for you UHR! By a process of elimination, you now know that the pump is OK. It's a) working and b) not over pressurising. Now you KNOW that the fault is within the mechanics of the needle valve and/or the displacement of the float (its inability to operate the mechanics of the needle valve). Both are very cheap so I'd say when you are repairing by replacement, always start at the cheapest part first. So replace the float, the float pin and the needle valve assembly and the float chamber gaskets. To be honest, I'd do both of them!

While you've got tops off the chambers I'd replace the hoses too. Make sure that the car is outside, on the drive and keep a foam or powder fire extinguisher handy as you're working with petrol. Clean out the fuel bowls while you're there too

[UHR850]

Many thanks Peter will try to get these parts,
they are very hard to get at the moment.

If you can help me to get these parts I will be very
great ful to you, all costs will be payed ofcourse.

Cheers, Kees

[UHR850]

Good news, the problem is solved thanks to
Peter's advice. I got from a classic car garage
in my village the top of a HS4 float chamber
with floater on it. I did swap the floater and
the pin who holds it. It was already better and
almost no play on it, I did assemble it again and
guess what ? NO leaking any more, the problem
was the play in the first place. I think the floater
got stuck in the chamber and couldn't stop the
petrol.

Happy again thanks Peter