Petrol leak from air fliters on all three carbs

[jamie101]

Hi everyone.
Me and my dad are having a little problem with the old etype again....
We have a petrol leak form all three carbs it leaks out from the air filters when the cars been at a while and also what seams to be a mix of oil aswell.
Any ideas? Or is a carb rebuild needed? (The carbs are SU's by the way)
We still have the slight misfire aswell on tick over after fitting the electronic ignition kit. Although she revs up lovley.....again any ideas?
Thanks in advance. J

[politeperson]

Have you checked to see if fuel is coming out of the three overflow pipes from the three carbs?

I assume your ignition timing is OK? The 123 tune green light is set to 10 btdc from memory so worth checking.

It sounds a bit like your float valves are not closing/ needles are not seated properly causing the petrol flood. When were the carbs last rebuilt? The diaphragms dont seem to last too long, The rebuild kits are £60 a carb from memory. Well worth doing if not for piece of mind, to stop the whole thing catching fire. Also some floats maybe failing as they are attacked by modern fuels. New plastic floats sound like the answer.

The oil sounds like it might be from the crank case breather. I find a bit of oil in the plenum chamber normal as these engines often breath quite heavily.

They seem to produce a bit of gunk and the breather pipe can get blocked. I assume yours feeds back into the air breather. Also I have seen the gauze in the head at the breather fitted backwards, causing excessive oil mist to run dun into the breather tube as opposed to drip into the timing case.

I fitted a catch tank!

[mgcjag]

Hi Jamie.....take off all 3 dashpots....remove each piston with the needles attached.....do not mix these parts up make sure each piston and dashpot goes back in the same position.....look in at the jet...the small brass tube the needle goes into.......if set correctly fuel should sit below the top....you need to blow into it to see it move.....all the settings are in the service manual.....if you switch on the pump the bowls should fill the floats rise operateing the needle valve and the fuel pump stop......the level should be as mentioned above......if fuel floods out you then need to investigate further....re oil......yes it can get messy if its never been cleaned..things to check as James mentioned.....Steve.....PS take care....if you have an extinguisher have it handy

[christopher storey]

You also need to check that the holding down cap for each float chamber lid has been correctly assembled. The correct order of assembly , working upwards is

Float chamber lid
Serrated Fibre washer
Overflow Banjo
Aluminium washer
Holding down cap nut

If these are not in the correct order, various untoward effects can occur including in some cases pressurisation of the chamber . However, my favourite would be leaking needle valves - either because they are defective, or because you are using an aftermarket pump such as a facet which may be producing excess pressure - the SUs need only 2.5 to 2.8 lbs/sq.in, and some aftermarket setups produce 5 or 6 which can cause flooding of the type you are experiencing - if this is the case a FilterKing pressure reducing device is the answer

[rfs1957]

The washers to which Christopher refers, serrated or internally splined, are indeed critical components as their cut-outs are what communicate atmospheric pressure to the float chambers - the thin pipes are meant to be air feeds as much as overflows.

So if they have been replaced by plain washers there will be all sorts of bizarre behaviour, as I can attest from experience.

If the original brass floats dont leak, keep them, they're better than anything plastic you will ever find.

[cactusman]

Agree 100% with Rory and Chris.... check the vents do vent. Check the float chamber valves are sealing. Check the floats float. Fish each out and shake. If anything slops about inside they are leaking. Get new ones...brass are available. If you are using a modern pump you will need a pressure reducer...what ever you do get the issue fixed though. Petrol gushing about is a recipe for catastrophe...

[JerryL770]

Agree, it sounds most likely either sunk float or sticking needle valve, but this reminds me of a problem we had with my carbs. I rebuilt my carbs with new parts from Burlen. Towards the end of the job I reported this in another forum

"Engine was running fine last week but we found an interesting problem this week when the ignition was turned on for some electrical testing. The front carburettor was flooding badly. The carbs had all been refurbished with a complete rebuild kit from Burlen including new floats and main jets with diaphragms etc. Had the float chamber top off to check the needle valve, all looked OK. Put it back, still flooding.

Took cover off again, fuel level was low, float at the bottom. Took the float out, seemed OK but swapped it for another - still flooding. Swapped the front float chamber lid with the centre one, front carb still flooding. Indeed we took all the dashpots off and achieved fountains of petrol from the front carb main jet. Took the float cover off again and still the chamber was empty but fuel had been flooding through. So question was: why had the float not risen?? Answer must be that the air above it was not escaping via the vent pipe. So removed that (the only item not swapped) and found it was blocked with solder where the pipe had been soldered into the banjo. Dismantled that and re-soldered but it was still blocked - the pipe was blocked too. So when that was sorted and refitted, problem solved! Phew!!"

We had all the correct washers in place but that did not allow sufficient air to escape from the float chamber whilst the petrol pump fed the fuel.

Also, with respect to the breather pipe from the front cam cover to the air filter plenum, there is a small hole in the underside of this which should be kept clear to allow any liquid (oil/water condensate) to drain out rather than get into the plenum.

[jamie101]

Thank you everyone for your replys help and advice.
First thing im going to check is the vent pipes as im sure they are pinched up on the ends for some reason!!??
See how we go from there. Im sure we will be able to sort it now with all the ideas here to go through and check. Thanks again everyone. Will update post when we hopefully get it sorted........