Fuel leak Weber DCNF 40

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Scalino
Posts: 179
Joined: Mon Jul 24, 2017 7:22 pm
Dino: Fiat Dino 2.4 Spider
Location: The Netherlands

Fuel leak Weber DCNF 40

Post by Scalino »

This afternoon I was tuning the idle circuit of the triple Webers on the spider after rebuilding them and noticed a severe fuel leak from the middle carb. It seemed to come out of the bottom of the float chamber (near the two lead plugs, definitely not above those), though I can't be sure as I was quite busy from keeping the gasoline to reach the hot engine (I had just driven it some 15 kilometers). I'll have a better look soon with a helper, a fire extinguisher nearby and a cold engine.

EDIT: I realised I had just filled the car up, I don't see how it could be relevant, but just in case.

During the rebuild we put the carbs in an ultrasonic cleaner (as seems to be normal with a carb rebuilt); could that make the lead plugs leak? I've searched and it seems the stuf we used (Tickopur R33) shouldn't give a problem.

Could a high fuel pressure cause it? I've been meaning to check it, but hadn't gotten around to it (needed to buy a gauge). As the car didn't run a pressure regulator that seems odd to me, although you never now after 40+ years (who knows what fuel pump might be in it).

Background;

We have been rebuilding the triple Webers of the Spider since it would die after seven kilometers. We completely disassembled them, but them in the ultrasonic cleaner for around 30 minutes and afterwards flushed them with water and thoroughly dried them. A lot of new parts were installed, apart from the gasket set: new mixture screws and springs, air correctors, all other springs, throttle valves, one spindle and the idle jets (stock jets). A bunch of parts were also zinc plated, so the carbs looked excellent. In the mean time we also replaced the throttle shaft running along the firewall with new bushes, the old ones were really tired.

We put it all back together, mounted them and double checked everything; all seemed good to go! So we went on the start the engine. Filled the float chambers and it fired up at the turn of the key, into a smooth idle. 8-) We were surprised to say the least. It went on to run well, but after 15 minutes I noticed fuel near the banjo bolts (quite a bit on the rear carb and a bit on the middle, none on the front one). Long story short, it turned out - it seems - to just the carbs spitting a bit a fuel, though I did replace all of the banjo bolts and fuel filter washers with bonded seals before concluding that.
However I'm also suspecting the lead plug in the top cover near the fuel filter, with todays addition.

With that leak sorted - by the looks of it at least - we went on with synching the carbs and setting the idle mixture. After that it drove great, a lot better than before. That was until the middle carb started draining itself from fuel...

Any ideas and/or similar experiences and advice are welcome!
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doublegarage
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Re: Fuel leak Weber DCNF 40

Post by doublegarage »

Not sure about the lead plugs - I know people who remove those for clean out and then re-solder them afterwards, but I've never head of them leaking after ultrasonic cleaning. They live in a place that vibrates a lot - I know ultrasonic vibration is different to a V6 at 6000rpm, but still I would expect those to be in there pretty tight.

I've had problems with the following things related to fuel leaks on Webers. None of them are necessarily related to your problem but one thought might lead to another...

Stiff tubing - the tubing gets stiff, then the hose clamps can't compress the rubber (or vinyl) like before - so you get a bad seal - replace all tubing and buy good clamps.
Shrunk tubing - the tubes between the carbs shrink and get shorter, this can pull the banjo off its seat - so as you tighten the banjo bolt, it feels like you're compressing the washer, but you're actually stretching the tube. Replace all tubes.
Bad fiber washers at Banjo - always replace these (x2 percarb, 2 different sizes), compress/tighten them well, then come back a week later and tweak them again
Scored surface underneath banjo bolt head - so the fiber washer can't fill the scratch that someone made when they slipped with the spanner.

Hope that helps,

-Richard
Scalino
Posts: 179
Joined: Mon Jul 24, 2017 7:22 pm
Dino: Fiat Dino 2.4 Spider
Location: The Netherlands

Re: Fuel leak Weber DCNF 40

Post by Scalino »

Thanks for the input Richard. We replaced the two hoses (badly needed) and also replaced the fiber washers with new ones. The fiber washers wouldn't seal, even after multiple times retightening. We opted to change them with bonded seals (steel washer with a rubber gasoline resistant insert) and checked the surfaces, which cured that leak.

However the new leak seems to come from the bottom of the float chamber, so that can't be related by washers. We haven't been able to have a look yet, maybe Sunday. I'll report back with our findings.
Scalino
Posts: 179
Joined: Mon Jul 24, 2017 7:22 pm
Dino: Fiat Dino 2.4 Spider
Location: The Netherlands

Re: Fuel leak Weber DCNF 40

Post by Scalino »

Well I've found the cause of the leak:

Image

One lead plug is just gone and it seems the other are leaking a bit as well. So, we'll take them of again and change all of the lead plugs to be one the safe side!
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