leaky carb

[stevo1980]

Hi i have found that one of my carbs on my 2 litre Aircooled is spraying fuel out from the top seal when i rev, this is why my bus stinks of fuel and the consumption is "pooh". How easy is it to replace the seals, i have never even looked at a carb until i went from diesel to petrol Aircooled. Been studying haynes but it dont really tell me much it only appears to be the top one but i might do them all as i can only buy a set.

[ghost123uk]

I don't know much about Aircooled, but a carb is a carb.

By "top seal" do you mean where the air filter connection joins the carb ?
Or perhaps the gasket ("seal")between the upper and lower halves of the carb ?

[stevo1980]

yeah sorry the gasket between upper and lower part of the carb.

[BOXY]

The petrol in the carb should be being sucked into the engine (negative pressure). If fuel is being sprayed out then something else is probably wrong. You shouldn't be getting a positive pressure in the carb apart from the fuel inlet into the float chamber. Has your van got the original mechanical fuel pump or has an electric one been fitted? If it's electric pump maybe the regulator needs looking at? The other possibility is if the inlet valves clearances are set too tight you might be pressurising the inlet manifold. Either way, fuel spraying out of the carb is a major fire hazard so make sure you've got an extinguisher handy when you're trying to fix it.

[ghost123uk]

Boxy is right I was assuming the spray was coming from the air filter connection and that would be a sure sign of pressure in the inlet manifold = either wrong valve clearance or a burnt out inlet valve (less likely). Fuel spraying from the gasket area is a bit odd.

If you do need to replace the gasket(s) it is easy to do, just take your time when cleaning up the faces after you split the carb. You need to remove all traces of the old gasket but not damage the relatively soft aluminium.

One thing, and someone else will have to answer = some carbs have a spring loaded ball bearing valve that can jump out (and always seem to vanish ) when you split the carb. I don't know if carbs fitted to Aircooled VW's have this "issue" to watch out for.

[stevo1980]

Ok thats a bit worrying.
here is a pic of where its coming from.

[faggie]

just buy a carburettor rebuild kit from the usual suppliers it gives you all the gaskets and diaphrams for the acelerator jets plus the fuel cut of valves

[BOXY]

The place the carb is leaking from is the fuel inlet / float chamber so there should be a positive pressure there from the pump. Check that all the screws that hold the carb together are tight. You might be able to stop the leak just by tightening the screws. It's worth checking all the screws & solenoids are tight every so often. I've had the venturi screw fall out both my carbs in the past.

[Footprint]

That's the float chamber, there should be no pressure there other than atmospheric*, and certainly not fuel under pressure from the fuel pump - the needle valve is the only area that is subject to pump pressure. I suspect the gasket has failed around the stub that supplies the accelerator pump diaphragm, which is in the lower part of the carb body, it's fed with fuel by gravity in the bottom of the float bowl, and when you shove the throttle it pushes it through drillings from the lower to the upper part of the carb and into the thin curved tube you can see in the carb venturi. This is why there is a squirt of fuel when you advance the throttle.

* The straight tube sticking upwards at 45ish degrees into the carb mouth is open and allows atmospheric pressure to act on the upper surface of the fuel in the float bowl, the pressure differential between atmospheric and inlet vacuum is what causes fuel to flow through the jets into the venturi.

[stevo1980]

Cool i think i will get the kit and do it myself. Wanted to ask too if its worth paying out and getting them striped and rebuilt by gasure.

[weimarbus]

If fuel is leaking from that part of the gasket it is likely that the float chamber is too full and the needle valve is not closing the fuel pump pressure as it should, in this case the engine would be running quite roughly as the mixture would be too rich called 'eight stroking' check the fuel level in the float chamber and adjust acording to Haynes manual. Better still to get them rebuilt and set up and know that they are ' right', if the consumption is that bad you will save the cost in fuel bills.

[Footprint]

When you look down the carb venturi with the engine running, is fuel leaking out of the float bowl vent, (the bit I mentioned earlier)? If no, then the needle valve isn't letting by.
The float bowl is NOT pressurised, the vent discussed opens the float bowl to the air intake - if the needle valve isn't shutting off fuel flow from the pump when the bowl is full - whether by being worn out, the float punctured or broken off of the brass arm, the float height set hopelessly wrong or by the needle valve being loose in the carb body, fuel will flow from the vent very easily, as there is no restriction to it at all.
If the gasket were totally goosed, or the screws holding the carb top on so loose as to not clamp the gasket at all, then it may well come out of the gasket as well, but there'll be some out of the vent.

[stevo1980]

Its all gettin a bit complicated for me now so i think im gonna go to gasure and have them overhauled. Only thing is im a bit reluctant to travel 48 miles to get there with leaking carb is there any emergency quick fix i can do to stop it leaking just to get me there.

[faggie]

if your going to the expence of having the carbs rebuilt, it would be more cost effective in the long run to fit a pair of reconditioned 36 or 40mm webbers or dellortos as spare parts are more available and you will gain alot more performance than the single barrel solexes can provide , or a cheaper option a pair of brand new webber 34 ict carbs

[stevo1980]

Just a quick update. Had the carbs refurbed by Steve at Gasure, well impressed with his work , fixed allsorts of problems with it. Drove straight from Gasure to manchester 50 miles or so and it drove like a dream so thanks for that Steve. Just need new engine mounts and thats the bus ready for road trips already.