MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Fuel Regulator

Hi, In the latest MGOC accessories book the fuel regulator on page 44 caught my eye. Over the years I've been troubled with fuel overflow from the HIF SUs on my 76 Roadster. I tried most things including grose jets but the problem always came back. In the end I fitted an old pair of HS4s, the overflowing stopped but the tickover is erratic because of the wear in them. Has anyone fitted this regulator to cure this problem, and did it work.
Thanks Chris Cummins
c cummins

What fuel pump are you using? SU's only need 1.5 psi a Facet pump supplies up to 7 psi depending on model, with fuel over flow it sounds like worn needle valve not closing..
K Harris

The AUF 300/AZX 1300 series SU fuel pumps supply an outlet pressure of 2.7psi (only the earlier, low pressure pumps that are mounted under the bonnet of the T series cars put out 1.5psi). If you are using a SU fuel pump, the pressure may be low if the pump is old and tired, but it won't be too high - the design of the pump is such that it will not over pressure the system. If you have an after market pump on your car, then you may need to use a pressure regulator, but not with a SU fuel pump. You can find my fuel delivery troubleshooting guide at: http://www.svmgcc.org/tech_tips/fuel_delivery.htm or check Paul Hunt's web site, The Pages of Bee and Vee at: http://www.mgb-stuff.org.uk/ for information. Cheers - Dave
David DuBois

Crud in the fuel bowls will prevent the needle from seating and cutting off the supply of fuel to the fuel bowl. If this is the problem, lowering the fuel pressure will not stop the fuel bowls from overflowing.
Kimberly

My experience with fuel pressure regulators is on weber convertions for porsches flat fours,240/260 Zs and MGBs,I would always recomend a regulator and Iwould not warrent againest leakage without one in place Ric
Ric Lloyd

With a Facet type pump a regulator is necessary, but I can see no benefit in fitting one with an SU pump!
Eric Martin

I eventually fitted a regulator, it works and cured all my fuel valve problems. I think it is more to do with modern fuels than the original system design.
I posted all the agony I had with this earlier, it was pretty intractable problem.
Stan Best

Thanks for the help, the problem happened with the OE su pump and the solid state I replaced it with. I spent an hour balancing the HS4s yesterday and tick over is a lot better.
At least with these I can clean the float chamber without taking the whole lot off, and the floats are fixed set.
I noticed that on other classics using SUs there is no overflow outlet on the float chamber lid, is this because they use mechanical pumps?
c cummins

I had intermittent problems for some time on my V8 with HIFs and SU pump. Changed valves and filters a couple of times but it eventually came back, always the same carb. Finally it continued to overflow despite another set of new valves, took another look and spotted fuel in the float - it wasn't that obvious without looking closely. Despite squeezing, shaking and heating the float I couldn't see any evidence of a crack so it must have been minute and sucking in a bit more fuel at each heat/cool cycle. Since fitting a new float there have been no more problems (so far!). Whilst Grose jets (jets?) were quite a popular change some time ago they seem to have fallen out of favour more recently. They were never that much better than a good standard valve, have been modified recently, and are now significantly worse, I hear.
Paul Hunt 2

I have one of those "other" classics, a Volvo P1800 with dual SU HS6 carbs. They do not have an overflow pipe like the HS4s on the MG, but they do have a hole covered with a small piece of aluminum to direct the overflow down onto the top of the float bowl. I guess they figure that's better than squirting it out over the engine.

Controlling the overflow on SUs is a fine balance of various factors, such as: dirt in the fuel, fuel pressure, needle-and-seat wear, needle-and-seat design, float level and float condition, for instance. If everything is reasonably adjusted, filtered and renewed, you shouldn't have fuel squirting very often. But the fact that overflow pipes and holes are standard should tell you something. -G.
Glenn G

The 'overflow' is primarily for venting *air* in and out as the float rises and falls, without it the float would never rise enough to shut the float valve and fuel would pump up the jet and flood the engine. Personally the MGB arrangement of piping any overflow down past the engine is more preferable to me than squirting it all over the float chambers, which are above the exhaust! Maybe Volvo float valves never leak ...
Paul Hunt 2

This thread was discussed between 02/03/2007 and 11/03/2007

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.