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Wedgetable

Fuel bubbling up vent tube on Zeniths, S1

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So... after a short drive getting the car up to running temp, I park it and get a snack. I come back to check on what may be leaking or burning or melting, and I see that there seems to be a lot of fuel backed up a vent tube on the forward carb, and bubbles are coming out the carb and travelling through the fuel in the vent.  This is while the car is sitting off.

 

It doesn't look like the level is really draining, and it's not dripping anywhere else, so fire extinguisher in hand, I start the car and everything seems fine.  After a few minutes driving I look back there and it's gone, and doesn't seem to have dripped out the carbs or the other end of the tube. 

 

Anyone got any idea what's going on here?  I've driven it another 50 kms or so in combination traffic and open road and haven't observed this again.

 

Here's a video I took of what was going on:

 

View My Video

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The fuel gets warm and vaporises, standard on carbs without a fuel return line to the tank. One of the reasons the Esprit can be hard to start in summer when it gets really hot. When the engine is running the flow of fuel into the carbs clears out the bubbles, it only happens when there is no flow and the fuel gets warmed up.

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One of the reasons the Esprit can be hard to start in summer when it gets really hot. 

So, why aren't ALL hot, carburated engines difficult to start then?


Cheers,

John W

http://jonwatkins.co.uk

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Mine certainly is difficult to start when hot and thats after an engine rebuild.

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So, why aren't ALL hot, carburated engines difficult to start then?

 

Myriad of reasons John, fuel quality, sate of tune, humidity, ambient temperature etc. You may just be lucky and have the perfect setup without realising it. In other words I don't know the answer to your question.

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Thanks for the replies. I will keep an eye on this when it gets warmer.  It just looks kind of scary having all the fuel backed up in a tube that just leads into the air box.

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Hi Wedgetable,

 

 

Those vent holes on the carbs should not have fuel in them as far as I understand, ever. They vent the air/fuel vapor above the fuel reservoir under the carbs to atmosphere, if the fuel level is so high that it rises up those tubes then its higher than the metering hole in the body of the carb. If fuel is that high up then it could be flowing out the mouth of the carb into the air box or the opposite direction into the intake manifold through the metering hole. The float chamber atmospheric vent is connected to that clear pipe you see through the body of the carb when the accelerator is at idle, when it is depressed the vent is redirect directly into the air box not through that tube. If you pressed the accelerator while starting for example the fuel in that line could be redirected into the air box. Not an ideal situation. While the others may be correct, that nothing is wrong, I would investigate the float chamber of the carbs and make sure that the floats are not stuck and that no passages are clogged.

 

Brian M.

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It could be that fuel vapour has condensed in the tubes?


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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The float chamber atmospheric vent is connected to that clear pipe you see through the body of the carb 

 

I'd assumed that the clear pipe was the fuel delivery pipe from the fuel pump, never worked on Strombergs so didn't realise it was a vent pipe.  :unsure:


Cheers,

John W

http://jonwatkins.co.uk

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Hey John,

 

Yeah the Federal model had the float chamber vent follow two different routes depending on if the accelerator is depressed or not. If its depressed it connects directly to the airbox through the face of the carb where the airbox attaches (theres a little hole beside the main carb opening) If the accelerator is not depressed it routes through those hoses to an electronic valve that depending on if the car is running or not either connects to the air box or routes through the charcoal cannister.

 

The reason I say there should definitely be no fuel in those vent hoses is because, on my car the charcoal canister and all that fun environmental stuff was stripped off and those vent hoses were simply routed directly into the air box and there was certainly no fuel coming out of them at any point. Unless thats what caused my engine fire, but my mechanic swears up and down it was electric so...

 

Brian M.

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Hi Wedgetable,

I looked at that video you posted again and noticed two things that I'd look at but that I don't think are related to your issue.
See the hose I've surrounded in green, that hose is the choke cross connect, it feeds fuel from the front carb to the back when the choke is on, but it should be on the outside of the metal tube and held with a hose clamp, yours look they are on the inside, I'd be concerned it would leak and for the cost of two hose clamps and some fuel line, its a very easy fix. Next look at the red box, you see that metal tube coming straight up, just bellow it there is a hose pointing down, it should be connect to that metal tube. If you trace the tube back to the other carb you see it connect to the same spot on that one and the other end goes off to some other things.
11jowut.jpg
If you just paid someone to refurb your carbs I'd be a little dissapointed in their work assuming they also installed them. You may also what to look at the fuel source hose, it looks a little bent there between the carbs where it fits between the T connection, probably nothing to worry about but you don't want it to be getting pushed or pulled.
Brian 

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Hi Wedgetable,

I looked at that video you posted again and noticed two things that I'd look at but that I don't think are related to your issue.
See the hose I've surrounded in green, that hose is the choke cross connect, it feeds fuel from the front carb to the back when the choke is on, but it should be on the outside of the metal tube and held with a hose clamp, yours look they are on the inside, I'd be concerned it would leak and for the cost of two hose clamps and some fuel line, its a very easy fix. Next look at the red box, you see that metal tube coming straight up, just bellow it there is a hose pointing down, it should be connect to that metal tube. If you trace the tube back to the other carb you see it connect to the same spot on that one and the other end goes off to some other things.
11jowut.jpg
If you just paid someone to refurb your carbs I'd be a little dissapointed in their work assuming they also installed them. You may also what to look at the fuel source hose, it looks a little bent there between the carbs where it fits between the T connection, probably nothing to worry about but you don't want it to be getting pushed or pulled.
Brian 

 

Thanks Brian,

 

The video is kind of crappy, but the choke cross connect is actually on the outside of the carb fitting -- I'll get some clamps on there.  Ah, the disconnected breather line in the red box -- that was me accidentally knocking it out. I just put it back in earlier. Good eye.  I checked the fuel feed line where you describe for the same pulling or pushing and it seems ok.

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Hi Wedgetable,

 

My car is of course missing a few parts including where those clear lines go. I was wondering if you could take some photos of what they connect to and where they route. I'm in the process of putting them back on my car but I'm not sure where they should be connected.

 

Brian

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Hi Wedgetable,

 

My car is of course missing a few parts including where those clear lines go. I was wondering if you could take some photos of what they connect to and where they route. I'm in the process of putting them back on my car but I'm not sure where they should be connected.

 

Brian

Hi Brian,

 

I don't have pics handy right now, but those clear vent hoses connect with the anti run-on valve, which is connected to the carb side face of the air filter box.

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Kind of blurry screencap from the video, but it shows the vent lines going into the ARO valve.

 

nf5xg2.jpg

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Thanks Albert,

 

I didn't realize you could see where it goes so clearly in the video. I've got another question for you, that pipe I highlighted earlier in red. One end goes to the other carb, but where does the other end go? If you could post a photo or video of its destination I'd really appreciate it, I suspect it goes to the mysterious charcoal cannister thats missing from my car.

 

Brian M.

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