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Saloon float chamber overflows

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Alpine Daimler
Posts: 189
Joined: Thu Feb 18, 2016 2:17 pm
Location: A tad west of Hamburg on the Elbe River

Saloon float chamber overflows

Post by Alpine Daimler »

Back again!

Following fuel tank relining, top end overhaul, rebuild including minor carb refurb / components check all is quite ok except for a persistant minor drip / incontinence from the overflow pipes onto the cross member, following shut down, I have since extended these tubes to spot this more easily.

When running or just with the ignition switched on the pump turns off when the chambers are full and all is fine, so the new Burlen supplied needle valves seem to be doing their job ok.

Twice now I have removed the float chamber caps, reduced the float/ fuel level a little to reduce possibility of fuel expanding and slowly getting out of the chamber and into the overflow pipes following shut down, removed the needle valves to check for cleanliness, all ok.

Where can the problem be? any ideas?

Regards
Rob C.

Christopher Storey
Helpful Person
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Posts: 404
Joined: Wed Mar 16, 2016 6:40 pm
Location: Cheshire

Re: Saloon float chamber overflows

Post by Christopher Storey »

It sounds like a leaking float . If you take them out and shake them, if there is a leak you will hear a rattle which is the fuel inside the float. I had persistent hot start problems because of this, so I bought a pair of the non-metallic stay up floats from Burlen, ( they are well worth the extra cost ) and have had no trouble since .

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Alpine Daimler
Posts: 189
Joined: Thu Feb 18, 2016 2:17 pm
Location: A tad west of Hamburg on the Elbe River

Re: Saloon float chamber overflows

Post by Alpine Daimler »

Hello Christopher,

I forgot to mention that I checked the floats, there seemed to be empty as I could not hear any sloshing around in there when shook and I sank them in fluid for a while and no bubbles escaped.

Strange that its both sides.

Regards
Rob

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Alpine Daimler
Posts: 189
Joined: Thu Feb 18, 2016 2:17 pm
Location: A tad west of Hamburg on the Elbe River

Re: Saloon float chamber overflows

Post by Alpine Daimler »

Well, having driven about 700 kms during the past week, half of which in, around, up and down the Alps and the old boy did pant a bit above 3000 feet in the temps and air humidity we have been almost enjoying and they were both still dribbling a tad on shut down causing onlookers/smellers/passer Byers to ask their companions if they too could smell petrol "Pfui!! kannst du Sprit riechen?"

The car performed wonderfully, I was pleased to have spent so much time lying under the car last year in a chemical warfare suit flushing out the cylinder block for what seemed like hours as the temp is a lot steadier, he still gets a bit hot under the collar , 90° c, when sitting in a high altitude traffic jam but no more. I have since compared the gauge reading with an infra red gauge reading and the team gauge in dash seems to over read a little.....better that way round!

After 5 years ownership I drove home for the first time ever in the dark, you have to just love those "glow worm" dash illuminations, good job I had a torch which I placed in my mouth most of the way home, heritage motoring, can't beat it.

Where was I? The carb overflows, well took the old boy back to the workshop and its residence, where incidentally one of the other fellows wife has coved 19 just to make life more interesting and much more importantly despite repeated start ups and shut downs the carb overflows don't leak any more and are dry as a bone, isn't life weird?

Keep well all

Rob C.

tjt77
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Joined: Wed Mar 23, 2016 7:01 pm

Re: Saloon float chamber overflows

Post by tjt77 »

if the floats are known to be good, the the issue is weeping float valves.. if you whack the top of the float chamber sharply with smallish brass hammer, it temporarily fixes the problem.. (till next time it happens) .. I have a friend who used to re-build carburetors for the 356 porches.. he 'bench tested' every pair of rebuilts on an engine he had set up for that purpose.... he had issues with new OEM float valves SOMETIMES being unreliable.. and had small drum full of 'new' duff float valves that had been discarded.. He eventually found a US manufacturer to make them to his standard..
The SU float valves come in various styles as thy have been updated over the years ..(originally brass with a solid alloy needle) there are also the US made 'grossjet' replacements.. which work well and last long time as long as not exposed to dirty fuel..
of the SU float valves (now supplied by burlen fuel systems in Wilts UK) the most effective ones are those with viton tipped needles.. but sometimes they dont always work perfectly.. its not always straightforward to determine the cause... and even very close inspection does not always provide answers as to why some new ones work perfectly from the get go, and others sometimes stick partially open.. try and switch your float valves for some 'other' new ones.. you could also check fuel pressure at delivery end.. SU float valve's should shut off cleanly in practice, with approx 8 PSI..
Additional Note..to combat the issue of carb float bowls dumping fuel after shutdown when in hot climates, on US spec Rover P6Bs the Rover factory used insulated float bowls with a moulded black foam about 3/8" thick.. may have been overkill, but the reasoning was that excess under bonnet temperatures were causing extra pressure in float bowls when airflow stopped.. causing the fuel to be dumped out of overflow..

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