3F Carb Draining issue (1 Viewer)

[Baron]

So this seems to be a common issue. I've read about 10 different posts on it, and affects 2F's as well. It seems some great idea's from Okie rebuild, to replacing seals, or doubling up on seals or polishing bits. BUT I cant find a single thread that end's in "Well that fixed it!"

Issue, Carb drains when its HOT after driving. It drains before your eyes in about 1min. The fuel I believe is ending up inside the Carb. Cant find any leaks, and when I look inside the Carb after it drains I can see the fuel on top of the flaps. Does not do it when cold, and it if it does not drain (which sometimes it does not) the fuel stays in the sight glass for days). I dont think this is a 'leak'' but instead is a siphon when certain things line up. I've got a video coming up showing (after 10mins and glass is empty) the fuel in the secondary (I already opened the throttle a bit. which likely emptied the main), I shake the car and open throttle again you can see 'mist''. Another vid shows fuel poring into secondary chamber straight after I turned the engine off.




The best detail seems to be from PinHead Carb bowl draining overnight - https://forum.ih8mud.com/threads/carb-bowl-draining-overnight.210532/ . But I cant find these holes he mentions to uinplug/clean up. I've tried the Okie rebuild and that did not help. I also bought myself a $100 carb on ebay just to learn how it works. The FJ62 has had a full rebuild except for core engine,carb. all hoses are new, PCV, Fuel filter, but Charcoal canisters and fuel pump are original) Engine actually runs well, but I think its uses fuel and I get the occasional hickup on a slow hill around 1800RPM, but I think thats a vac advance issue)

Some thoughts I had:

1. Siphon into the Carb idea. I would have thought that the aircleaner would not allow a 'suction' to draw fuel into the carb. Also, the problem happens with air-cleaner off. so its not sucking.
2. Capillary action. Likely not to drain it in under 60 sec
3. Pressure in Fuel tank. Their is none, and the return is above the fuel

Is it possible something is 'pushing' air into the float chamber thus pushing fuel out? Maybe next time I see it, I'll start pulling rubber hoses seeing I have 60second while it happens! (I did run the car twice attempting to reproduce it, but it wouldn't. Shows how it needs a specific set of circumstances). Or is a certain position of 'valves' creating an environment under the flaps? In the first video you can see the 'mist'pushing up from the body?

Has anyone who has seen this issue got a solid picture of what they fixed?

 

[CruiserTrash]

I’m gonna follow this. I just did my first carb rebuild for my 2F Aisin and it’s doing exactly this. In the first 4-5 minutes the fuel level goes from the middle of the sight glass to the bottom, and after 10-15 minutes it’s empty. The fuel is going first into the notes, then sneaking past the throttle blades, and ending up in the intake.

Don’t discount the fuel boiling from heat and condensing elsewhere, outside of the bowl. I’m still trying to puzzle out that possibility.

 

[Spike Strip]

Modern Gas is MUCH different than the stuff available in 1985. It's formulated now to be under high-pressure for fuel injection, to burn cleaner, lower NOx, VOCs, blah, blah, blah..... The Petrol is probably boiling in the float bowl and pushing the fuel out the various venturi openings. I see this frequently in mine. You can actually see the gasoline boiling through the sight-glass if you look at it immediately after shut down. Additionally, you'll get capillary wicking of the fuel over-night, and you'll find a puddle on the intake plenum.

I plan to eventually add some hood louvers to decrease the under-hood temps and hopefully alleviate some of the fuel-boiling and vapor lock issues of carb'd engines on RFG (at least that's here in USA, anyway).

 

[Baron]

Modern Gas is MUCH different than the stuff available in 1985. It's formulated now to be under high-pressure for fuel injection, to burn cleaner, lower NOx, VOCs, blah, blah, blah..... The Petrol is probably boiling in the float bowl and pushing the fuel out the various venturi openings. I see this frequently in mine. You can actually see the gasoline boiling through the sight-glass if you look at it immediately after shut down. Additionally, you'll get capillary wicking of the fuel over-night, and you'll find a puddle on the intake plenum.

I plan to eventually add some hood louvers to decrease the under-hood temps and hopefully alleviate some of the fuel-boiling and vapor lock issues of carb'd engines on RFG (at least that's here in USA, anyway).

Yea I looked at that. Appreciate the ideas.

- Possible boiling. I stuck a temp sensor on Carb (dual sensor with alarm, I used for radiator). does not get above 30deg, and you can easily touch it.
- Wicking overnight - yes possible, but this is draining in seconds.

 

[CruiserTrash]

@Spike Strip There’s a fuel station nearby with ethanol free. I’ve been running that regularly and it hasn’t made a difference. You’re absolutely right that our “normal” E10-E15 sucks, but getting rid of the corn hasn’t solved my problem.

 

[Baron]

So not a lot of progress. I decided to 'practice' the idea of opening the hand-throttle each time I stop. This is in the hope to release any pressure coming up from the engine valves. while I've not have a complete drain of the carb, its not starting as easily as it normally does. i.e. take 3 seconds to crank, instead of the usual 1. I can defintely tell its not the same, but the draining issue did not return, though a test of 1 day is hardly going to solve it. On other issues I found a vac issue in the AC idle up circuit, but it goes nowhere near the carb. AC idle up was not working correctly but not it is.

 

[Baron]

Update on this. I think opening the hand throttle helps (when I stop car, after a hot run, I open hand-throttle, to remove pressure come from engine into the carb, which could be sucking fuel out of the carb-bowl). Its not fully difficult to start when it happens. Just to update, this is not an issue you can easily repeat, its not every time you stop the 60, only sometimes. Its more when its hot, definately. Because I use the hand-throttle method, its not completely drained the carb, so I've not been able to test the other posibiliies (vacume in one of the many other pipes to the carb). I guess I'm just going to learn to live with it.

 

[Baron]

Hopefully the final update on this. I spoke to a proper Carb guy. He describes the issue as Syphoning. Just like a Syphon, when you start a flow it keeps on going, and apparently thats what happens. its a bit of a fluke to get the right conditions for it to happen. the result is Fuel just keeps on flowing out of the jets, after you stop the car. (thats what I saw). The carb has a air tube that is means to prevent this, and if it gets clogged up, this is the result. anyway, My Carb was fully serviced. two other issues were found that might have helped in. The secondary throttle diaphragm has a hole, which means the entire secondary was never working. Also the throttle pump rubbers were inverted for some reason. Went for first drive and no issue, so we will see what happens.

 

[CruiserTrash]

Hopefully the final update on this. I spoke to a proper Carb guy. He describes the issue as Syphoning. Just like a Syphon, when you start a flow it keeps on going, and apparently thats what happens. its a bit of a fluke to get the right conditions for it to happen. the result is Fuel just keeps on flowing out of the jets, after you stop the car. (thats what I saw). The carb has a air tube that is means to prevent this, and if it gets clogged up, this is the result. anyway, My Carb was fully serviced. two other issues were found that might have helped in. The secondary throttle diaphragm has a hole, which means the entire secondary was never working. Also the throttle pump rubbers were inverted for some reason. Went for first drive and no issue, so we will see what happens.

Any photos? I’d love to get a visual on this stuff.

 

[Baron]

Any photos? I’d love to get a visual on this stuff.

Nah sorry. Some video's above of some issues. Now I've got a nice clean Carbi and its working well. I did see the diaphram and it had about a 1/2 inch tea in it, so no chance of holding suction.

 

[Baron]

So update on this issue. After a full carb recondition, the issue is still present. (after a 3000km drive) Its become rarer however, possibly! It now only occurs after very long drives (3hrs). When I pull up to fuel, the engine will be struggling to idle (this is the signal of problem will occur), and try to stall. I'll go fill the car up, but while i'm doing that the carb drains (its not because I'm filling up, because its done it at other times). If I pull the hand-throttle, it seems to 'ease' the when I start the car again (my theory, is that opening the carb valve eases vacuum(, but if I dont do that, the carb drains completely, and I need to turn the engine over for 10seconds for it to start. (pulling the hand throttle, means it starts in maybe 4-5 seconds, and does not idle nicely, needs a touch of throttle for 20seconds). When the problem does not occur, starting is perfect. 3 seconds to solid 650rpm idle.

I still think its a suction or pressure issue somewhere. The fuel is being pushed or sucked out the carb jets into the engine (I've got video's of this). The carb guy said their is small pressure relieving holes all through the carb, and his reco should have fixed it (have not gone back to him, at that was 6 months ago).

My next focus is on the fuel-tank vapour recovery and the carbon canisters. Its very possible I connected something wrong (remember, I rebuild this entire car, and didn't exactly remember where everything went). Also the carbon canisters could be old.

This issue does not re-occur all the time, and its not affecting normal driving at all, just annoying that is the last thing I cant fix.

 

[OSS]

Try a different grade & brand of gasoline. It may be rapidly evaporating out of the float bowl. More like boiling actually.
In the USA, some types of gasoline evaporate very quickly. Float bowl is empty next day.

 

[Baron]

Try a different grade & brand of gasoline. It may be rapidly evaporating out of the float bowl. More like boiling actually.
In the USA, some types of gasoline evaporate very quickly. Float bowl is empty next day.

Nah, it drains in a minute, and I even put a temp sensor on carby. I then took a gopro video down the carb throat while it was stopped and you could see the fuel poring out of the jet into engine. Quite a few people have this problem, but normally just think that it takes a little more time to start. Been a few threads on it.

 

[CruiserTrash]

Nah, it drains in a minute, and I even put a temp sensor on carby. I then took a gopro video down the carb throat while it was stopped and you could see the fuel poring out of the jet into engine. Quite a few people have this problem, but normally just think that it takes a little more time to start. Been a few threads on it.

Good on you for using a go pro.

 

[OSS]

The USA 2F engine’s original carburetor has a large vent pipe going into the float bowl. That pipe leads out to a biggish hose that leads to the charcoal canister. It’s purpose is to ventilate the float bowl gas vapors to the charcoal canister when the engine is off.

The vapor flow in the hose is controlled by a big solenoid valve (outer vent control valve) which opens when the engine is off, but shuts when the ignition switch is on.
I don’t know if the 3F has that setup.

If the 3F carburetor has a float bowl vent pipe too - leading to the charcoal canister, it’s not impossible for some sort of back flow to occur if things are wrong at the charcoal canister — forcing gas tank vapors back through the charcoal canister and back up through the vent hose into the carburetor. That scenario would definitely push the gasoline in the float bowl out into the engine during shutoff.

The evaporative system would have to be really messed up for the above situation to occur — but yeah, I’d go through it carefully. Something is pushing the gasoline in the float bowl into the engine. Normally it doesn’t do that.

 

[CruiserTrash]

The USA 2F engine’s original carburetor has a large vent pipe going into the float bowl. That pipe leads out to a biggish hose that leads to the charcoal canister. It’s purpose is to ventilate the float bowl gas vapors to the charcoal canister when the engine is off.

The vapor flow in the hose is controlled by a big solenoid valve (outer vent control valve) which opens when the engine is off, but shuts when the ignition switch is on.
I don’t know if the 3F has that setup.

If the 3F carburetor has a float bowl vent pipe too - leading to the charcoal canister, it’s not impossible for some sort of back flow to occur if things are wrong at the charcoal canister — forcing gas tank vapors back through the charcoal canister and back up through the vent hose into the carburetor. That scenario would definitely push the gasoline in the float bowl out into the engine during shutoff.

The evaporative system would have to be really messed up for the above situation to occur — but yeah, I’d go through it carefully. Something is pushing the gasoline in the float bowl into the engine. Normally it doesn’t do that.

This was discussed on one of the other threads pertaining to the float bowl drain issue.

I installed the AC Delco canister and plumbed it correctly, including the judicious use of one tee fitting, since the replacement canister has three ports, and the Toyota four.

I still get woosh at the fuel filler when removing the cap. I still get fuel smell after the truck sits for 10-30 minutes on a hot day. I did immediately on install. Can’t figure it out and gave up.

 

[Baron]

Thanks guys, This is real usefull

 

[Combat Wombat]

Have you checked if there is a gasket in the carb that may be blocking a port?
Some carb kits have small holes in alternative locations to suit california/saudi/aus carbs (not all are the same because of emissions and octane etc)
Only other thing I could think of is perhaps a blocked fuel tank vent, or the vent is connected to something its not supposed to be.

Ive had nearly a years worth (literally) of tinkering and figuring out vac lines and have saved a fair bit of images and diagrams.

Above, is from an Australian FJ60, sticker on the intake pipe just after air filter housing.
Below, is a Saudi Fj60, has a switched advance signal to the dissy for some reason!
(maybe so the dissy advance could be disabled when running shyte octane fuel or some soft limiter engine protection)

 

[Baron]

Have you checked if there is a gasket in the carb that may be blocking a port?
Some carb kits have small holes in alternative locations to suit california/saudi/aus carbs (not all are the same because of emissions and octane etc)
Only other thing I could think of is perhaps a blocked fuel tank vent, or the vent is connected to something its not supposed to be.

Ive had nearly a years worth (literally) of tinkering and figuring out vac lines and have saved a fair bit of images and diagrams.View attachment 3718281
Above, is from an Australian FJ60, sticker on the intake pipe just after air filter housing.
Below, is a Saudi Fj60, has a switched advance signal to the dissy for some reason!
(maybe so the dissy advance could be disabled when running shyte octane fuel or some soft limiter engine protection)
View attachment 3718283

Hey, Wombat,

Can I pick your brain about this. The diagrams, which should be roughly the same are not. In the AUS one, the middle carb pipe goes to a canister (assuming its fuel related). In the bottom one, the middle one goes to the Vac Advance (which for my Aus , is another pipe entirely).

I did some testing today. That Vac Switch (Top Carb Pipe) on my 89 FJ62 seems stuffed, the Vac line has suction when the engine is running. BUT, I'm not getting any volts on the input wire (I'd assume its an ignition feed), and the Vac Switch itself is constantly blocked (even when 12V applied). I cant find any reference to what that switch does, I also cant find any suitable replacement, I'm not even sure if its normally open or normally closed (its closed now). I don't support you know much about it?

 

[Combat Wombat]

I have a folder of 3F pics (sounds kinky hey) on my garage PC. I dont know what the switch is yet, mine was buggered with and random lines everywhere....

I saved this pic ages ago which seems legit...