Fuel leaking from carburettor vent

T

typonaut

Member
When I say “leaking” I mean positively p*ssing out - it's that much that externally I though it was a water leak.

Anyway - 1975 2200SC: there's a "vent" to the front side of the carb, which is hidden (on my car at least) by a bracket that bolts to the carb and supports the heat shield. Could not really see where it was coming from, but removing the bracket reveals it clearly.

I write "vent", because that is how is it marked in the Haynes manual.

Is this the overflow from the carb bowl, that is indicating that the float valve is not working?

Other symptoms: car has cut out a few times, and/or has no power, indicating fuel starvation. I initially thought this was running out of fuel, so pulled the reserve, but later realised this was not the issue at all (because I put the reserve back, and it still kept running). How much air should there be in the fuel pump glass dome - I only seem to be getting fuel just above the filter.

Also, do I need to worry about using E10 unleaded? Car probably has never had a carb overhaul, and has been in storage for nearly 25 years (so was probably using leaded fuel the last time it was running around).

Should the timing be different with E10 unleaded?
 
Hi, Yes, float valve problem. Be aware that it could also be flooding into the inlet manifold and into the cylinders. Which is why it cuts out and loss of power. You will find the fuel in the sump with the oil, check dipstick for level and smell of petrol.

Colin
 
AC glasstop fuel pump, fuel usually above gauze, air pocket in top of glass.
Flooding will rob power, and cause bad running.
 
I suffered with this, same model and year. The float valve was to blame, was sticking open, and hence fuel kept on coming, and yep, pulsed out the overflow. I freed it at roadside a couple of times, polished the plunger part, would be fine for a week or two, then occur again. Finally replacing valve and float, then setting float as per manual, been fine since. I changed the oil also, didn't seem to much fuel in it, but just in case.
 
Having looked at the Haynes manual, it seems to me that one has to remove the entire carburettor in order to get at the float/needle valve. Is that correct?
 
typonaut said:
How did you do that?
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I tried tapping the fuel bowl, but to no avail. Removed air filter, then fuel line, then carb (hif). Removed bottom plate, float spindle, float, inner plunger of valve. Blew threw it, reassembled. Not very pleasant at roadside, stinking of fuel, knowing my wife wanted to say 'are you sure this old car is reliable enough'. After the second time that was enough for me (at side of A9, car shuddered every lorry that passed, and it rained), and hence replacement valve and float. I still never saw a reason for the old set up to go wrong, but it's not happened since replacement so something was definitely not right! I obtained the new bits from Wins as I recall.
 
Not convinced ethanol was my problem (leastways not the stuff in the fuel!) but hey, only an opinion, I'm usually wrong! Hasn't happened since, and using same fuel. Haven't spotted debris in fuel filters. Only thing that I have found to go to bits, which could well be due to ethanol was the o ring in the fuel reserve tap. It was hard and breaking up, new one easy to fit though and ethanol resistant. It's difficult to say with my car though, as it hadn't had decent long runs for many years until I bought it, so many things failed initially, likely due to suddenly being awakened. Two years now of running, something else going awry, replacing, and I am feeling a lot more confident in reliability, as everything that can leak has, everything that cannot spark when it should has, and all the grumbles and squeaks settled down!
 
Mick Rae said:
It's difficult to say with my car though, as it hadn't had decent long runs for many years until I bought it, so many things failed initially…
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Until July, mine had not moved for 25 years - so I suppose it's to be expected that some things might need attention. :)
 
Similar situation then, same model, same year, same rude awakening. I had to replace radiator, heater matrix, ignition bits, servo, pads, brake light sensor, exhaust box, alternator, all failing one at a time. None with any warning (well, that I noticed). It got a bit of a pain, as I am more driver than fixer, and had sold a really sorted classic I had for a long time to get a P6. But I am glad I've stuck with it, as it's a lovely car to drive, looks great (to me), and is suitably different. And, well, for the last month at least, totally reliable, and really no reason to expect it to not be so long as I keep on top of it all, and most importantly, drive it a lot.
 
Well… I bought and fitted the SU service kit, which includes a new float valve and inlet cylinder (!?), and it all seemed tickety-boo… for about five miles… Then it started pouring fuel from the overflow vent again.

After quite a lot of faffing around I am more than a little disappointed.

Is there anything else I should try?
 
A couple of thoughts.

(1) Have you got a fuel filter fitted between the fuel pump and carb? If you have debris in the fuel system that can stop the float valve from sealing (you mentioned the car was laid up for years before starting - that can cause dirt in the tank from sitting)

(2) Does it happen on hot days? I fitted HIF6’s to my TC a few years ago and had the same problem, flooding when warm after a few miles of driving. I eventually noticed it happened when it was 31°f out. I added extra heat insulation to the original shield. Since then it’s never been a problem. Fuel in New Jersey can contain up to 10% ethanol, ethanol lowers the boiling point of fuel hence the problem.
 
New float as well yeah? Check it's no hanging up on spindle? Set as per manual in terms of height there isn't a lot to go wrong if it's all free. Unless there is much coming through. Strange it's come back again. And a pain in the the backside!
 
sdibbers said:
A couple of thoughts.

(1) Have you got a fuel filter fitted between the fuel pump and carb?.
Click to expand...

There is only the filter in the fuel pump - there's no debris in there, and I didn't notice any when I disassembled the carb to do the float valve and seat, and seals.

sdibbers said:
(2) Does it happen on hot days?
Click to expand...

The first time it happened, I suppose coincidentally, was after I picked it up when having a new clutch fitted. Although the mechanic tells me he took the engine out to do the clutch, I am struggling to think of a connection between the two events.

That day was fairly warm - but I'd first driven to the supermarket, without issues, and the car was parked in its underground car park, where it was reasonably cool. It was probably parked for about 30mins (after being driven about two miles), and cut out when waiting to leave the car park (so was probably running for about a two minutes).

Yesterday (which was apparently the hottest day of the year in the UK - 32 degrees), when it happened again, after the carb had been serviced. I'd driven it about five miles (at about 19:00 - so cooling down), and did not notice any issues. I then left it in a car park for about 90 minutes, drove less than a mile and the power just went, got it along about another half mile to park, and found that it was leaking fuel from the vent again.

So, I don't think ambient heat is an issue, because the car hadn't really time to get hot each time it has happened (or at least when I noticed).
 
I replaced both the float and it's spindle as the spindle was a bit secondhand looking! Old float didn't have and fuel inside,but I figured replace everything and hopefully not have to go there for a while :thumb:
 
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