3F Carb Draining issue (1 Viewer)

[Baron]

Thanks mate, I've actually figured out what it is, but no closer to solving it.

It is a Vacuum Sensor, for the Idle Fuel Cutoff. It earths to ground, when Vac goes above a level. That ground signal goes to the yellow computer box in the passenger footwell, which this controls the fuel-cut-off. I've bypassed my cut-off, so I dont think I need to worry about it. This thread talks about it. Aisan Decel Fuel Cut Circuit - https://forum.ih8mud.com/threads/aisan-decel-fuel-cut-circuit.989475/

However, more concerning is the layout of the three Vac-Pipes at the top of the Carb. Your picture above, and another one I found on the internet has the Vac sensor on the pipe closest to the Fender. However the 'Vac Layout Diagram' on the Air-Intake Pipe, suggests that it should be the one closest to the engine? So right now, I'm on a mission to figure this out.



I also found another thread that talks about Vacuum pressures in the Carb, and how the Idle Fuel Cutoff works. Aisan Decel Fuel Cut Circuit - https://forum.ih8mud.com/threads/aisan-decel-fuel-cut-circuit.989475/
It talks about the possibility of mounting the Carb base-plate upside down (or having a non-standard baseplate), as it has some channels in it, which drive pressures around the Carb doing things. So I'll be checking that on the weekend as well.

 

[Combat Wombat]

I just remembered like 3 min ago, yes its for a decel cut off circuit switch!
Have you got access to a decent vac gauge?
I used a really old one (it was installed in the 1980's) and tested each port (hooked up a T-piece) and found that some of the ports were higher or lower than the other. They weren't all the same (even the manifold ports are different pressure, at idle and also under load)
This also includes what is the correct vac port for distributor advance (probably the most important) if I hook it onto a 'high vac pressure' port, the advance is rotating and the timing is then WAY too advanced for idle/initial start up.

The other diagram which may solve it is the fuel vapour lines/emissions?

PS: That pic I posted, that member ended up getting a 1HZ and sold off the 3F gear.
There isnt a guarantee that the routing is correct, it just looks ok-ish in regards to it all being there!

 

[Baron]

Just to document some steps taken.

I followed CruisIUnders process here:

I originally deactivated the Idle-Fuel-Cutoff, which meant I re-wired the cables to permanently power-on the solenoid. Today I had some time, so I wired it back up correctly, and re-tested with the above process. It turns out, my Vac Sensor is faulty. With or without clamping the vac tube to it, when I go over 2K RPM, I get the misfire. (in reality, its a mis-fire pulse. The engine, every 3-4 seconds, misfires, drops RPM, but comes back again).

I redid the dactivation and it returned to normal. I actually suspect I fried the Vac Sensor. When I thought it was a switch, I connected it to 12V directly, and the jumper wire I used, got hot, then stopped. The Sensor now has Zero resistance, and when I suck on the input, no change to grounding, so I think its stuffed. I'll get a new one.


My investigations then moved to the two Charcoal Canisters. I ordered the ACdelco, BUT looking at this diagram from a 2F;

You can see that the canister has inbuilt valvles. The 2F have 3+air ports, the 3F has 2+Air ports. When you pull them out and test them.
- The small port (which connects to Carb) has a Valve one way.
- The large port vents to Air
- The small port, also vents to air.


Hence, I cant see how any overpressure or underpressure, would ever get past the charcoal canisters and impact Carb drain. Any pressure from TANK or CARB will vent to Air? This is on both canisters. Hence I dont think this is the issue.


Next I looked at the Outer Vent Control Valve. in a 3F, this is a large pipe from the TOP of the Carb. It goes through what looks to be a one-way valve, to the Control Valve, and then to the charcoal canister. I could'nt find ANY documentation on this, even Amaya does not have any diagrams. Its called a Bimetal Thermostatic! Thats it!!! NOW when you start to play with it
- Its seems to be a one-direction valve, BUT one way is 100% blocked and the other is 60%. So its one way, but not good.
- However, it you apply a blow-torch to the small end, aimed to the middle of it. Its 10% blocked in both direction. Hence once hot, its pretty much open in both directions (but the outer control valve only switched on (passes gas) when the engine is OFF. i.e. When you turn the engine off, the Carb is vented via this circuit. When engine is ON, this air pathway is blocked.

Hence, when this bimetal thing is hot, it opens up. BUT when would it get hot!!! The answer was hard to find, again I looked at the 2F diagrams. When the engine is fully HOT, and turns OFF, apparently Fuel in the carb bulb gets hot, and evaporates. That 'gas' goes out the top-carb pipe, hits the bimetal valve,heats it up, the valves opens, and goes via the outer vent (which is now open, as the engine is off), to the charcoal canister through to air (via charcoal).

However, I imagine if something is not working properly, Pressure could flow the other-way (back into the Carb), filling the float, and forcing fuel out the jets. BUT I cant figure out how that pressure would build (it could certainly come thought the charcoal canister from the Fuel Tank) because the charcoal canister is vented to air via the bottom air-vent?? Does not make sense.


So I still dont think I've solved the carb-draining issue, but I'm going to replace the fault vac-sensor switch, re-enable Idle-Fuel-Cutoff and see what happens. I'm going to return the Charcoal canisters I ordered as these DO NOT have the internal valve. Every port can be positive or negative pressures (you can blow or suck), which is NOT what the OEM ones do. Strangely, the OEM ones are different in the port-size, BUT the function are the same. Both have and internal valve on the small port, the the large/small port vent to bottom/air port.

I still cant believe that their is no 3F Emissions manual. Their is a 2F and a 3FE, which are both very detailed on the complexities of these items. BUT the 3F (Aussie spec), seems to only have half the components (no BCV etc) and no diagram showing how they all work together. HENCE I'm having to test each and every bit.

 

[CruiserTrash]

Just to document some steps taken.

I followed CruisIUnders process here:

View attachment 3726119

I originally deactivated the Idle-Fuel-Cutoff, which meant I re-wired the cables to permanently power-on the solenoid. Today I had some time, so I wired it back up correctly, and re-tested with the above process. It turns out, my Vac Sensor is faulty. With or without clamping the vac tube to it, when I go over 2K RPM, I get the misfire. (in reality, its a mis-fire pulse. The engine, every 3-4 seconds, misfires, drops RPM, but comes back again).

I redid the dactivation and it returned to normal. I actually suspect I fried the Vac Sensor. When I thought it was a switch, I connected it to 12V directly, and the jumper wire I used, got hot, then stopped. The Sensor now has Zero resistance, and when I suck on the input, no change to grounding, so I think its stuffed. I'll get a new one.


My investigations then moved to the two Charcoal Canisters. I ordered the ACdelco, BUT looking at this diagram from a 2F;
View attachment 3726121

You can see that the canister has inbuilt valvles. The 2F have 3+air ports, the 3F has 2+Air ports. When you pull them out and test them.
- The small port (which connects to Carb) has a Valve one way.
- The large port vents to Air
- The small port, also vents to air.


Hence, I cant see how any overpressure or underpressure, would ever get past the charcoal canisters and impact Carb drain. Any pressure from TANK or CARB will vent to Air? This is on both canisters. Hence I dont think this is the issue.


Next I looked at the Outer Vent Control Valve. in a 3F, this is a large pipe from the TOP of the Carb. It goes through what looks to be a one-way valve, to the Control Valve, and then to the charcoal canister. I could'nt find ANY documentation on this, even Amaya does not have any diagrams. Its called a Bimetal Thermostatic! Thats it!!! NOW when you start to play with it
- Its seems to be a one-direction valve, BUT one way is 100% blocked and the other is 60%. So its one way, but not good.
- However, it you apply a blow-torch to the small end, aimed to the middle of it. Its 10% blocked in both direction. Hence once hot, its pretty much open in both directions (but the outer control valve only switched on (passes gas) when the engine is OFF. i.e. When you turn the engine off, the Carb is vented via this circuit. When engine is ON, this air pathway is blocked.

Hence, when this bimetal thing is hot, it opens up. BUT when would it get hot!!! The answer was hard to find, again I looked at the 2F diagrams. When the engine is fully HOT, and turns OFF, apparently Fuel in the carb bulb gets hot, and evaporates. That 'gas' goes out the top-carb pipe, hits the bimetal valve,heats it up, the valves opens, and goes via the outer vent (which is now open, as the engine is off), to the charcoal canister through to air (via charcoal).

However, I imagine if something is not working properly, Pressure could flow the other-way (back into the Carb), filling the float, and forcing fuel out the jets. BUT I cant figure out how that pressure would build (it could certainly come thought the charcoal canister from the Fuel Tank) because the charcoal canister is vented to air via the bottom air-vent?? Does not make sense.


So I still dont think I've solved the carb-draining issue, but I'm going to replace the fault vac-sensor switch, re-enable Idle-Fuel-Cutoff and see what happens. I'm going to return the Charcoal canisters I ordered as these DO NOT have the internal valve. Every port can be positive or negative pressures (you can blow or suck), which is NOT what the OEM ones do. Strangely, the OEM ones are different in the port-size, BUT the function are the same. Both have and internal valve on the small port, the the large/small port vent to bottom/air port.

I still cant believe that their is no 3F Emissions manual. Their is a 2F and a 3FE, which are both very detailed on the complexities of these items. BUT the 3F (Aussie spec), seems to only have half the components (no BCV etc) and no diagram showing how they all work together. HENCE I'm having to test each and every bit.

I’m not sure if this helps. In the US we have two things that control the venting to/from the evap canister on a 2F.

One is the “outer vent control valve” that is attached directly to the evap canister bracket, it sits right on top of it. It plugs into the wiring harness as well. The other is a VCV (pictured below) on the carburetor side. This part is still available from Toyota. You obviously have the 2F and missions manual so you can see how it’s all plumbed together.

On our US 2F trucks, this part is black and white. At this age, every single one of them is bad - I’ve tested maybe 12-15 and have never found a good one. The above black/blue unit comes from the 80 Series and is identical except for one vacuum nipple that faces a different direction.

Even if the carby 3F motors used different equipment, perhaps one of the puzzle pieces could get replaced with the unit above. Maybe you just craft your own evap system with whatever parts are available in other words. Again, the 2F emissions manual will show exactly how that part works. Hopefully any of this is helpful.