Race Engine Forum UK

Hey all,

Just a quick question. I have been having quite a lot of fueling problems lately and I currently have a cheap and nasty pump. The problem is that when I have my foot flat especially in 4th and 5th it starts to starve and cuts out. I then have to idle along and rev to get some fuel going again. This was quite embarrassing at the track the other day :)

I have now been given a high pressure pump off a 200sx which runs a turbo with about 1.2bars pressure. It is a submersible pump so I will have to make a plan somehow. And run a inline regulator, I found one which has a pressure gauge and return so all good there :)

Now my question is, will this actually work? My volumex is currently boosting 0.5 bar (according to the boost gauge) so what sort of fuel pressure will the carb need and be able to take?

Thanks
Geoff

Do you run carburator with that high pressure pump? If so then this may be the problem. You do not need that much fuel to be pushed to the carb as it may flood when the needle valve opens due to too high fuel pressure. Please correct me if I am wrong but a 3 bar at the carb seems to be way too high.

Hey

Sorry I should have been more specific here. I meant to say that the pump came off a car that runs 1.2 bar turbo pressure.

jazzygeoff wrote: I have now been given a high pressure pump off a 200sx which runs a turbo with about 1.2bars pressure.

And I am running a stock standard 36 carb on the VX with a standard pressure pump at the moment (see picture).

I have also noticed that if I floor it uphill it tends to run out of fuel pretty quick and will cut out, so you basically have to easy the throttle in which obviously doesn't help lap times.

I'm sure with the regulator I could bring the fuel pressure right down, just not sure if this will be a overkill or if it will strain the fuel pump with such high regulation. I really don't want a fuel pump to burn out in my fuel tank.

You don't need a high pressure fuel pump with 'suck-thru' carburetion because the float chamber is not subjected to boost pressure.

2 to 5 psi pressure (running engine) measured at the carb, with 0.4 gall/min free delivery (ie: into a bucket) is perfectly adequate on that setup. No more! If you run more than that you'll probably lift the needle of the seat and flood the carb. No way should you use an injection pump, far, far too much pressure.

You need a bit more fault finding but I'll just point out that in 9/10 cases where I advise on Vx units the problem is chokes too big, faulty ignition pack or too-high ex back (static) pressure...

Get a Facet Silver Top interrupter.

GC

The VX cars actually did come with a fuel injection pump from the factory as they ran a bosch roller cell type pump the same as the beta i.e. and similar to many mechanically injected cars. These pumps are a little different to what you will find in the nissan though, they are an old design and have a wider operating range.

Quite correct, thanks.

Important to stress however that they carried a fuel pressure regulator that turned the pressure way down to a manageable level for carburettor delivery. The probleme with changing to an alternative is that if you don't have a regulator that is adjustable plus gauges to calibrate it the chances of reducing the delivery pressure to the correct & low level stated above in my prev post are slim to say the least.

GC

All the Volumex / Volumetrico fuel pumps I have seen (Lancia 037, Lancia Beta VX, Fiat 131 Volumetrico) all use the same fuel pump as the Lancia Montecarlo / Scorpion. That pump is a carbon vane, rotary fuel pump that delivers 6 PSI maximum. That amount of pressure (6 PSI) would not even be close for a fuel injection system, mechanical or electronic. That same pump was also used on the Fiat 131 and several other Fiats and Lancias.
Those pumps are very reliable but do develop a intermittant problem after years of use. The end of shaft of the pump is "D" shaped and fits in a "D" shaped hole in the impeller that hols the vane plates. The "D" on the shaft wears, but does not wear evenly. Because of this, axial movement of the shaft can jam the impeller, stopping it. The fix? File the "D" portion of the shaft so that it is the same shape as the worn portion, this will prevent wedging of the shaft and impeller. It does not last forever but will last a a few years.