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.