Leak - Carburettor Flange

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hiltow
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Leak - Carburettor Flange

Post by hiltow » Tue May 08, 2018 9:55 pm

I've noticed a small leak of what looks to be a kind of light green mix of petrol and oil that leaks from the front offside corner of the rubber carburettor flange and seeps down onto the inlet manifold (will try to get a picture up if I can work out how to).

The problem seems to begin right from cold start-up, when the choke is in operation. It's difficult to tell whether the leak is coming from the upper carb / flange join, or the flange / inlet manifold join below.

I last replaced the flange with a new (genuine) item around 6 years ago and this problem still seems to happen (the car hasn't been used a lot in the meantime). Torqueing the fixing bolts hasn't solved the problem.

Just wondering:

1 - if it's possible to install a new flange without fully removing and disconnecting the carb from the coolant hoses?
2 - has anyone else had this problem / it is a common fault?



mark1gls
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Re: Leak - Carburettor Flange

Post by mark1gls » Tue May 08, 2018 10:18 pm

There is coolant running around the inlet manifold from the head near cyinder 3 and the little rubber o ring can leak coolant, could it be coolant you are seeing?


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hiltow
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Re: Leak - Carburettor Flange

Post by hiltow » Wed May 09, 2018 11:02 pm

No, the leak is coming from the metalastic / rubber carburettor mounting, not the inlet manifold to the cylinder head.

Definitely not coolant - it is fresh oil / petrol coloured (golden).



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unknownmale
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Re: Leak - Carburettor Flange

Post by unknownmale » Thu May 10, 2018 12:40 am

1. Yes, unbolt the three bolts on top of the carb to lift it off the mount, then remove the 4 bolts holding the mount on. (But I would just take the hoses off, it'll be easier to remove the rubber mount/ clean etc, there wont be much coolant in the hoses and you can use hose clamp tools to keep it getting everywhere.

2. Leaking rubber flanges are common, but not fluid, air. It's unlikely to be leaking fluid from the rubber mount to be honest. If it's oil, then perhaps it could work its way down the carb once switched off from the breather/ recirculation...but not much. Petrol could if the needle and seat was not sealing so the bowl overflows, but again unlikely. Coolant is the most likely leak here.

If you're seeing oil around the base of the rubber mount i'd suggest the rocker cover gasket would be the likely cause. Pictures would help!


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hiltow
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Re: Leak - Carburettor Flange

Post by hiltow » Thu May 10, 2018 10:57 pm

IMG_Leak.jpg
OK, now posted a picture that shows the substance of the 'leak' spilling forward of the flange between the first and second inlets.

It's tricky due to the lighting / things in the way to get a close-up of the flange itself, but the leak definitely isn't coming from the join between the flange and the inlet manifold as the thickness of the flange itself has the muck on it (leaks don't go upwards!).

What you see here happens when the car is started from cold and carefully warmed-up (car is currently on SORN, so wasn't driven). Also noticed tonight that the gasket between the upper and lower halves of the carb seems saturated, presumably with petrol - the gasket itself is fairly new and not given problems before.

I had the original Pierburg completely rebuilt with new (genuine) parts 8 years ago by a specialist, and the car isn't used regularly. When it was rebuilt, the round metal bi-metallic strip choke control unit (which is on the nearside face of the carb) wasn't chilled before it was refitted - I think this might be relevant, as the position of the expanding metal strip inside is designed to move (expand) with temperature.

This meant it was refitted set a position of being at room temperature of 20c as being a 'cold' start-up temperature, whereas it should have been chilled down to say below 5c to reflect a cold day when it needs to give more choke on start-up. The Upshot of this now is that in cold temperatures, when the car starts from cold it is being given perhaps too much choke (and hence fuel) through the initial few minutes of the warm-up phase (2000 rpm). However, when I started it last weekend when the picture was taken (and during the heatwave when the ambient temperature the car was in was 24c), the revs during that phase are more normal, at 1500rpm.
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james butler
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Re: Leak - Carburettor Flange

Post by james butler » Fri May 11, 2018 6:55 pm

clean it off with car cleaner then see where it leaks from.
its allready been said but the rubber carb flanges are rubbish unless you can get a genuine vw one so if its split then you will have issues.
the breather from the rocker box has been known to throw up oil so it might be worth giving it all a thoroughly good clean including the mesh gauze in the rocker box to help it stop doing it.
first things first is to give it a clean and see where its coming from, because you say its over the carb body im inclined to think its oil from the breather lining the airbox and coming out around the join between the airbox and the top of the carb thus dribbling down the outside
i used to have a pool of oil on the inlet manifold that came from the airbox joint where the airfilter is fitted, i only found out after changing the rocker gasket for the umpteenth time.


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hiltow
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Re: Leak - Carburettor Flange

Post by hiltow » Tue May 29, 2018 9:41 pm

Spent some time on this over the week and, good news - I've managed to solve the problem.

I'd have been surprised if the flange gasket was split, as I replaced the original (which was fine) with a new genuine item for preventative maintenance 8 years (though only 800 miles) ago. New rocker cover has been fitted, so the breather side of things is fine.

After removing the air cleaner and checking it and the side of the carb, I could see that the leak was coming from between top join between the carb and flange gasket. I loosened the three bolts securing the carb to the flange and was able to lift it up off the flange to carefully clean the mating faces with a paper towel. The inside of the flange seemed quite wet with petrol.

I refitted the carb bolts and retightened, but not quite as tight as before and the problem has now gone - it was probably that the bolts had been refitted a little too tight causing the flange gasket rubber to warp slightly in use leading to a gap where the fuel was coming out.



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Re: Leak - Carburettor Flange

Post by mark1gls » Tue May 29, 2018 11:00 pm

Good to hear you managed to solve the problem. :-D


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hiltow
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Re: Leak - Carburettor Flange

Post by hiltow » Mon Sep 03, 2018 9:22 pm

Old thread - new problem! The leak of the oily petrol substance (as per the photo above) has now unfortunately, returned.

On tickover yesterday, after noticing that the golden-coloured staining on the top of the manifold had returned in the same place, I leant over to take a closer look but was shocked at what I saw.

For a second, a pulse of the stuff squirted out (seemingly under pressure) between the bottom of the carburettor body and the rubberised mounting gasket and then evaporated. That only happened once. Engine runs fine.

I'm surprised by this because the carb is bolted tight against that gasket. Of course, there's no visible gap in the seal, so for the liquid to be pushed out like that would have to be under quite some pressure to force its way past the seal. Another clue is that the cardboard gasket between the upper casting of the carb and the lower appears to be saturated.

Obviously, this is probably based on petrol, but what's causing it to happen and how can it be sorted out?



mark1gls
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Re: Leak - Carburettor Flange

Post by mark1gls » Tue Sep 04, 2018 10:44 am

The engine does vent it self from the rocker cover into the air box then into the carb which is normal, have you cleaned out the metal gauze underneath the rocker cover as that can get blocked and possible the engine is having trouble breathing until the pressure is high enough then it pushes past any blockage?

Other option is fit a oil catch can from the rocker but check the breather 1st.

I remove the rocker cover, block up the breather hole then pour in some GUNK engine de-greaser and leave it to soak over night then blast some water through the breather hole to wash any dirt out then leave in the sun to dry out. Good time to give the rocker cover a quick coat of paint.


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hiltow
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Re: Leak - Carburettor Flange

Post by hiltow » Wed Sep 05, 2018 9:37 pm

Thanks mark1gls. I put a brand new rocker cover on a few years ago now, though the car has probably done less than 1000 miles since then, so should still be clear?

When I get chance, I'll take the air cleaner off to see whether there's any signs of oil being sucked through into it.