Fuel leak - SU carb, any ideas?

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Nissanman
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Re: Fuel leak - SU carb, any ideas?

Post by Nissanman »

As per normal, my O/F tubes were trimmed off short when I got the car.

To reinstate them to the original design I made up those two sump supports: -
fueloflowpipegrommets.jpg


Just a small metal tab with a grommet one end and a 1/4" spacer on the other.
The spacer allows the tab to clear the return on the pressed metal sump.

Bending up the new rigid pipes to fit was quite an exercise because I did it with the engine in the car :roll: :roll: :roll:
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Nissanman, just trying to help.
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Re: Fuel leak - SU carb, any ideas?

Post by purplehaze »

Wow, those are awesome!

Very clever Nissanman

And jayhayden, why are the plastic ones better? My originals seem fine, seem to float ok....
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Re: Fuel leak - SU carb, any ideas?

Post by purplehaze »

And joe, I did pull open up the piston and saw just a touch of gas near the jet
Float floated well, oil in the pots, tuned it by ear and Uni-syn and already loving it more
May remove the carbs, or see if I can remove the the big jet/mixture thingy from the bottom to clean it out, without removing the carbs
Possible?
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Re: Fuel leak - SU carb, any ideas?

Post by cbez »

was it crud in the needle?
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Re: Fuel leak - SU carb, any ideas?

Post by purplehaze »

I didn't find any crud in the needle (yet) but might dissect the lower mixture 'screw'

Float was working fine, but I suspect some crud jammed up the needle or jet

It's running beautifully now, of course, so I hate to tear it down
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Re: Fuel leak - SU carb, any ideas?

Post by jhayden »

purplehaze wrote: Tue Mar 01, 2022 7:03 pm
And jayhayden, why are the plastic ones better? My originals seem fine, seem to float ok....
The brass floats eventually develop vertical hairline cracks along the sides, allowing fuel to leak in and leading to the "sunken float" Sid mentioned.
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Re: Fuel leak - SU carb, any ideas?

Post by purplehaze »

Thank you Jon, apologies for butchering your name
That makes sense now
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Re: Fuel leak - SU carb, any ideas?

Post by jrusso07 »

purplehaze wrote: Tue Mar 01, 2022 7:13 pm And joe, I did pull open up the piston and saw just a touch of gas near the jet
Float floated well, oil in the pots, tuned it by ear and Uni-syn and already loving it more
May remove the carbs, or see if I can remove the the big jet/mixture thingy from the bottom to clean it out, without removing the carbs
Possible?
This IS a wonderful group of people, and I'm so grateful to have helpful advice on these quirky little cars we all love
Glenn
Some good news Glenn. I would not recommend removing the jet assembly from the carb unless the carbs are removed from the manifold. I have never done it that way and would think it would be a bitch to get it out and back in with all the linkage and such under the carbs.

You said in the original post that it cleaned itself up. It may have been an intermittent condition due to crud somewhere but seems it corrected itself. If the bowls are clean, and banjo bolt filters/screens are clean, you might might be good to go after addressing the fuel overflow tubes.

Have you run the car for any length of time? Does it not leak now?

I had an odd condition with a fuel hose to the carbs. After a short time running, I would smell gas...couldn't find any leaks until I ran my hand on the old, braided fuel hose feeding the carbs from the pump. It felt cold - like gas feels on your hands. Turns out the rubber inner hose had cracked, and the outer braid was hiding the leak - just a thought.
Last edited by jrusso07 on Fri Mar 04, 2022 12:37 pm, edited 1 time in total.
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Re: Fuel leak - SU carb, any ideas?

Post by purplehaze »

Thanks a lot, Joe

Your braided fuel line leak is odd, so rare. Guess I'm 'lucky' to have old rubber ones to see leaks

Yeah, it seems to have cleared up, no leaks. I think it was feeling neglected, wanted some attention.....and I have to admit I feel better after doing some tuning again. It's so satisfying!

Thanks for the tip about removing the carbs to access the jet assembly. I'll keep that in my back pocket for now
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Re: Fuel leak - SU carb, any ideas?

Post by garcia_vm »

Love this site.
My Fairlady is no beauty queen. But when I got her, I did drive her home. She needs a lot of work, but did run. I've only turned her on a few times since I brought her home, just to move her in and out of the garage. Well, on Friday I wanted to take her for a spin, and noticed she was struggling to stay on. don't have a Choke cable so I just had my foot on the pedal.
Long story short, I smelled gas, turned it off and noticed lots of gas. Looked like the water hose was on. I got online and started reading anything I can find on SU carbs.
Looks like i have to clean out the float bowl. Wish me luck
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Re: Fuel leak - SU carb, any ideas?

Post by Nissanman »

Where was the gas coming from?
Make sure that the float bowl overflows extend way down to the sump or they will pee fuel all over the exhaust.
I think you can work out where that would go :oops: :shock: :oops: :shock:
Nissanman, just trying to help.
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Re: Fuel leak - SU carb, any ideas?

Post by garcia_vm »

OK, so I have no idea what I'm doing lol.
the top part where the needle is, looks clean. The bowl has a lot of fuel, is this normal?
When I was putting back together, I noticed that the plunger has a metal dot. Does that dot need to be at a specific position when assembling?
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Re: Fuel leak - SU carb, any ideas?

Post by Gregs672000 »

Think of it as working the same way your toilet does... a float goes up as the fuel level increases and turns off the flow of fuel, constantly refilling itself but not overflowing UNLESS the float does not float (is there any gas inside the float? Shake it!) Or the valve does not seat (worn out and leaks even when closed)... you should not be able to blow air through it when the valve arm is pushed up as it would be when full of fuel.
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Re: Fuel leak - SU carb, any ideas?

Post by Gregs672000 »

The carbs can leak around the brass washers that connect fuel feeds too. I would consider replacing the old floats with the plastic ones as the brass will eventually sink I hear., unless their stupid expensive (never priced them).
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Re: Fuel leak - SU carb, any ideas?

Post by redroadster »

You were lucky with the arcing from the alt brushes so close by I always dreaded fuel inj minor seepage usually a big pain to deal with for the $
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