Fuel Return Valve Issue?

[dom14]

Hey guys,

I thought the fuel return valve was working fine after doing few tests on it(RB30 carby model), but apparently it isn't.
RB30 fuel return valve is "piggy backed" via engine RPM sensor unit.
Basically, when engine rpm hits around 1500 or more the Fuel Return Valve closes & effectively allow less fuel to return
back to the tank, which in turn increases the fuel pressure when engine's under load or accelerator pedal is pressed, allowing more fuel to the fuel bowl(carby).

My carby's been having issues with rich mixture(carbon soot build up on spark plugs) and hesitation when mixture is leaned to address the excessively rich mixture issue.

I can't say for sure, but it appears blocking the fuel return line and stopping fuel from getting to the fuel return valve appears to have fixed the problem.

Does this mean I've been having a fuel pressure issue, rather than a carby issue(rich mixture)??!!

Blocking fuel return line has improved the carby float level as well. Before it was very low.

Do I have a malfunctioning RPM counter unit(I think it's under the dashboard in driver's side) or a malfunctioning
Fuel Return Valve?! Or do I have a week fuel pump(in tank stock pump was used)
How does that having more fuel pressure improve excessively rich mixture issue?

Doesn't low fue bowl float level mean leaner mixture, rather than richer mixture?

Thanx

[garett]

do these carbys have a gauze before the needle and seat ? if it has a tiny bit of dirt it can give you a low float lvl. incorrect setting of the float arm might also give this low lvl. a fuel pressure gauge would be handy on this one after you check the float lvl setting.

[mudnut]

Have you checked the voltages present at idle and above 1500 rpm? What is the resistance of the coil?. After confirming that there is no voltage at idle, I would remove the solenoid and check to see if it is seating /sealing properly. Does it click in and out when given a 12 volt feed? Follow the procedure in the manual to release the fuel pressure before removing the solenoid.

[dom14]

Another thing I forgot to mention was that without blocking the Fuel Return Line, the float bowl would not get any petrol at all.

It did earlier, but not anymore. Fuel was pumping, it's not getting into the carby float bowl.

I'm guessing the fuel pressure is not high enough and when I block the fuel return line, the fuel pressure goes up a bit and carby float bowl fills up??!!

[dom14]

Have you checked the voltages present at idle and above 1500 rpm? What is the resistance of the coil?. After confirming that there is no voltage at idle, I would remove the solenoid and check to see if it is seating /sealing properly. Does it click in and out when given a 12 volt feed? Follow the procedure in the manual to release the fuel pressure before removing the solenoid.

I didn't check the voltage, but I tested it following the way you outlined in the RB30 thread by checking the fuel flow from the Fuel Return Valve when revving the engine. When I rev the engine, Fuel Return Valve clicks & pretty much blocks the fuel flow on fuel return line. So, I thought it was working the way it suppose to(allowing less fuel to return to the tank).
I'll check the voltage at 1500 rpm and above & resistance & other tests you mentioned above, shortly.

[dom14]

do these carbys have a gauze before the needle and seat ? if it has a tiny bit of dirt it can give you a low float lvl. incorrect setting of the float arm might also give this low lvl. a fuel pressure gauge would be handy on this one after you check the float lvl setting.

Yes, they do. There's a gauze outside the carby(bunjo bolt with a gauze filter in it) at the fuel entry, and then also gauze filter in the accelerator pump plunger/piston, but they are pretty clean, no blockage. Just to be safe, I'll change the fuel filter as well. Float arm is apparently bit low, 'cos fuel level in the float bowl is always bit lower than half, but i though it was ok.

As you advised, I should check the fuel pressure straightaway. I'll do that shortly.

[dom14]

Have you checked the voltages present at idle and above 1500 rpm? What is the resistance of the coil?. After confirming that there is no voltage at idle, I would remove the solenoid and check to see if it is seating /sealing properly. Does it click in and out when given a 12 volt feed? Follow the procedure in the manual to release the fuel pressure before removing the solenoid.

I checked the voltage on the wires.
I got bizarre readings at first. At idling it was showing no voltage then revved it jumped into incrediable 30+ volts.
I thought it must have been a momentary fault with the multimeter.

I stopped the engine for few seconds and restarted and did the test again.
This time it shows 13.6v at idling & jumps to zero when revved to around 1500 rpm or more.

I'm still wondering whether the power to the Fuel Return Valve from the rpm sensor/sender is somewhat faulty, though
above bizarre reading might have been from a multimeter fault, 'cos

There's no way rpm sender/sensor unit can produce such amount of voltage?!!!!
What do you think?!

[mudnut]

Without popping the case for the ERS I couldn't tell you what sort of signal it could produce. It deals with a pulsating voltage so if it has reactive components such as chokes and capacitors, theoretically (if the right fault conditions exist ) it could produce a voltage spike.

Also a faulty solenoid coil can produce a spike as the magnetic field collapses. A lot of solenoid coils can have a zener diode or capacitor to kill the spike.

I would do the test again with another meter and use a knockometer (plastic handle of a screwdriver) to gently tap test the components and wiring harness.

Did the solenoid click in and out with a 12 volt feed?

[dom14]

Without popping the case for the ERS I couldn't tell you what sort of signal it could produce. It deals with a pulsating voltage so if it has reactive components such as chokes and capacitors, theoretically (if the right fault conditions exist ) it could produce a voltage spike.

Also a faulty solenoid coil can produce a spike as the magnetic field collapses. A lot of solenoid coils can have a zener diode or capacitor to kill the spike.

I would do the test again with another meter and use a knockometer (plastic handle of a screwdriver) to gently tap test the components and wiring harness.

Did the solenoid click in and out with a 12 volt feed?

Solenoid definitely clicks, 'cos I can always hear it, even from inside the car when driving.
BTW, resistance between the pins of the fuel return valve solenoid is 24 ohms.

I basically disconnected the wire goes to the Fuel Return Valve solenoid and checked the voltage at idling & revving high.

When you said, "Also a faulty solenoid coil can produce a spike as the magnetic field collapses. A lot of solenoid coils can have a zener diode or capacitor to kill the spike",
Did you mean the RPM sensor/sender unit under the dash that forwards the voltage to the Fuel Return Valve?

I know about that unit from RB30 thread, but I have no idea on how to test it? I'll have to read your posts in RB30 thread again.
It basically picks the signal from the ignition coil and translates that into forward voltage accordingly, doesn't it?

Since it's an electronic unit, it's prone to fail just like any other unit, isn't it?
And that means, if the RPM sender/sensor unit doesn't work properly, then vehicle won't be running properly under load, 'cos it may end up starved of necessary fuel pressure to fill up the float bowl with necessary level of fuel?
That kinda produces symptoms that are consistent with weak fuel pump/pressure or carby float issues, doesn't it???!!

Come to think of it, RB30 carby patrol isn't that simple after all, even though it's apparently less complicated than EFI RB30.
Electronic things can go wrong inside and it can still leave you with plethora of problems.(Like the case in mine with Fuel Pump Control Unit).

[mudnut]

Yep. The return valve coil. And as you have said, if the valve is receiving a feed over 1500 rpm or it is not seating properly, it might cause the problems you have cited. I wonder if you can get hold of another valve and ERS. If there is a break or reduction of signal to the ERS it might let the valve open at the wrong time.