The USA spec fuel cap fitted
to many MGB’s & Midgets was unvented and as a result sometimes there
is a big suck of air when you undo the fuel cap. – to such an extent
that the bottom of the tank on the Midget of ours with such a cap gets
sucked up a couple of inches and there’s a big metallic clang when the
cap is taken off and the tank fills with air! rubber auto oil seals Subaru. The obvious question that then arises is whether this affects the fuel delivery from the pump.
Our experience is that it does occasionally play silly beggars with the fuel flow but not often. It seems that the only time it interrupts fuel supply is when fuel is low and the bottom of the tank is sucked up the pick-up is left high & dry on an island of tank bottom with the fuel around the edges. And the gauge is fooled – reads nearly 1/2 too! We have learned that when the fuel gauge starts to increase it’s a warning of this about to happen!rubber auto oil seals Subaru.
So in summary the non-vented cap doesn’t seem to inhibit fuel delivery when the tank is at negative pressure. And presumably the very large number of cars sold in the USA would attest to that too!
The original SU pump is very reliable for about 12 – 15 years.
Once it starts to falter, overhaul it and it will be good for another 12 – 15 years.rubber auto oil seals.
The SU pump only ever had one problem – that when it did get old and tired and falter, it would respond to a tap (which eventually becomes a hit as it gets worse) and start working again. Thus, people would not get around to overhauling it (just give it another hit), yet mutter about the unreliability (hit it again) of it every time they had to crawl under the car and HIT IT. So was born one of the great urban motoring myths! Of course it was unreliable then – it was worn out! It’s a bit like running tyres worn through to the cords and wondering why you lose the air so often!
FIX IT, DON’T HIT IT!
A new set of points and a new diaphragm (include new valves for a belts & braces approach), all correctly adjusted as per the workshop manual, and it will run happily for another 12 – 15 years. As simple as that!
Finally, (for what it is worth) avoid the electronic SU clones – I get a lot of feedback about them failing.rubber auto oil seals Subaru.
If your pump operates too rapidly, There are only five possible causes:
No petrol in tank, or faulty pick-up
If the system has been opened up – the pump is not yet primed (quite common) This can happen when it is working against air pressure and the air pressure confuses the pump’s valves) To check, disconnect the outlet hose of the pump from the pipe going forwards to the engine and operate the pump until petrol comes out the hose. If air comes out initially, this is likely the problem. Reconnect and the pump should then operate for a while until filling the carbs, after which it should slow to a click every 5 – 10 seconds as per normal.rubber auto oil seals Subaru.
Air weeping into the intake line at a joint (this is possible even though there is no petrol weeping out). Double check all joints for tightness.
Grit under the valve in the pump (sucked through from the tank) Clean out tank.
Faulty valve in the pump. Renew valve.
Not convinced? Here’s something to reflect on:
When electronic pumps get to the end of their life they die completely, and no amount of hitting or anything else will persuade them otherwise. So, when an electronic pump falters way out in the boondocks, there’s nothing for it but a long and expensive tow home. What price then an SU which a gentle tap prods into life.rubber auto oil seals Subaru.
Our experience is that it does occasionally play silly beggars with the fuel flow but not often. It seems that the only time it interrupts fuel supply is when fuel is low and the bottom of the tank is sucked up the pick-up is left high & dry on an island of tank bottom with the fuel around the edges. And the gauge is fooled – reads nearly 1/2 too! We have learned that when the fuel gauge starts to increase it’s a warning of this about to happen!rubber auto oil seals Subaru.
So in summary the non-vented cap doesn’t seem to inhibit fuel delivery when the tank is at negative pressure. And presumably the very large number of cars sold in the USA would attest to that too!
The original SU pump is very reliable for about 12 – 15 years.
Once it starts to falter, overhaul it and it will be good for another 12 – 15 years.rubber auto oil seals.
The SU pump only ever had one problem – that when it did get old and tired and falter, it would respond to a tap (which eventually becomes a hit as it gets worse) and start working again. Thus, people would not get around to overhauling it (just give it another hit), yet mutter about the unreliability (hit it again) of it every time they had to crawl under the car and HIT IT. So was born one of the great urban motoring myths! Of course it was unreliable then – it was worn out! It’s a bit like running tyres worn through to the cords and wondering why you lose the air so often!
FIX IT, DON’T HIT IT!
A new set of points and a new diaphragm (include new valves for a belts & braces approach), all correctly adjusted as per the workshop manual, and it will run happily for another 12 – 15 years. As simple as that!
Finally, (for what it is worth) avoid the electronic SU clones – I get a lot of feedback about them failing.rubber auto oil seals Subaru.
If your pump operates too rapidly, There are only five possible causes:
No petrol in tank, or faulty pick-up
If the system has been opened up – the pump is not yet primed (quite common) This can happen when it is working against air pressure and the air pressure confuses the pump’s valves) To check, disconnect the outlet hose of the pump from the pipe going forwards to the engine and operate the pump until petrol comes out the hose. If air comes out initially, this is likely the problem. Reconnect and the pump should then operate for a while until filling the carbs, after which it should slow to a click every 5 – 10 seconds as per normal.rubber auto oil seals Subaru.
Air weeping into the intake line at a joint (this is possible even though there is no petrol weeping out). Double check all joints for tightness.
Grit under the valve in the pump (sucked through from the tank) Clean out tank.
Faulty valve in the pump. Renew valve.
Not convinced? Here’s something to reflect on:
When electronic pumps get to the end of their life they die completely, and no amount of hitting or anything else will persuade them otherwise. So, when an electronic pump falters way out in the boondocks, there’s nothing for it but a long and expensive tow home. What price then an SU which a gentle tap prods into life.rubber auto oil seals Subaru.
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