Technical 28IMB question
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Technical 28IMB question
smart51
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It's best to return it to the fuel tank, or at least to a T connector in the engine bay. The fuel in the carb can heat up when the engine is switched off and still hot. It makes hot starting quite difficult.
Thats interesting as the 26IMB doesnt have that second outlet. Does that carb have hot staring issues?
smart51
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I have a 28 with the return blocked off and I have had hot starting issues. I'm guessing, but I wouldn't have thought they'd pay to add it if it wasn't needed. I wonder if it eases the load on the fuel pump a bit, as the excess is pumped back to the tank.
Im having a fuel starvation issue. I disconnected the supply to the carb and tried sucking the fuel through but felt there was air entering the pipe somewhere and wondered if that was via the return pipe I have from the second outlet
smart51
Established member
The pump should be able to feed more fuel than the engine can use at full throttle at max revs. Any air in the fuel should be dissipated through the carb. I think you'd have to have a massive air leak to dilute the fuel enough that it would cause problems.
If you drive the car and get the starvation problem, what happens if you lift off the throttle for a few seconds then get back on it? With the engine still running and the throttle closed, the fuel pump should be able to refill the float bowl. When you get back on the power it should run OK, at least at first.
If you drive the car and get the starvation problem, what happens if you lift off the throttle for a few seconds then get back on it? With the engine still running and the throttle closed, the fuel pump should be able to refill the float bowl. When you get back on the power it should run OK, at least at first.
Problem is I haven’t driven the car since rebuilding it. The engine has run a few weeks ago and ran very well, but now Ivevtried starting to no avail. I noticed the fuel had drained completely from the fuel filter by the tank which is why I tried sucking the fuel through. There’s an air leak somewhere
the hobbler
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The fuel running back into the tank when the car is left for some time is an on-going problem that a number of Forum members seem to have suffered. I have obtained an old petrol-tank filler-cap, removed the inside parts of the cap and then fitted an old schreader valve onto the top of the filler-cap. Being that tyre-fitting shops change the valves from Alloy wheels quite often, they can be a source of such a valve---you need the type that is secured to the wheel by a nut the runs on the threaded lower section of the valve. With this filler cap in place instead of the normal cap, the fuel-tank can be GENTLY pressurised which will force fuel from the tank through to the fuel-pump. I cannot take the credit for this idea---it came from Matt Pasquali (jump-jet)
You can cap that return pipe and things should be no worse than if using the earlier carburettor. The return alternatives shouldn't affect the amount of fuel reaching the carburettor.
It's possible that the fuel pump isn't being actuated by a long enough stroke of the rod from the cam. If the engine has been apart the fine spacing of gasket and packer might have been upset. You also get fuel starvation if the pump is loose.
Different pumps, (even new ones), aren't necessarily perfectly dimensioned to an engine, and different packing gaskets may be needed.
In general I have found that when in good condition and properly set up against the engine block, all mechanical pumps fitted to any version of these engines will supply far in excess of the fuel required; hence the solution, on later versions, of the return pipe.
the hobbler
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There is a specific amount that the fuel-pump's operating rod should stick out passed all the gaskets and the spacer when the rod is JUST ABOUT TO START extending (i.eat its fullest IN)--that is between 1 and 1.5mm. The easiest way to measure this is with feeler gauges put together to add up to the amount required---I normally aim for the 1.5mm setting.
I think this is def my next thing to check, thanks
Took the pump off and removed one of the gaskets as slightly too thick. Also the air was getting in through the carb via the return pipe whist I was sucking on the supply pipe. Sorted that and the engine fired up with no issue, hurrah!!
