HS6 carbs Leaking ( again )

[paul staines]

Thought I had fixed this. Carbs fully re-furbed by Burlen at great cost. Paid extra for stay up floats and Viton tipped float needle valve. When first fitted we had trouble with either the front or rear carb overflowing from the float chamber. After swapping parts from one chamber to another we got them to work. Car ran ok for 600 miles. Left for one week and fuel pouring from back chamber again. tried tapping it with no luck. Tonight will strip and check again.I have fitted fuel filters before and after the fuel pump. The fuel overflows straight onto the manifold shield. How bad a design is that !. Could the float chamber bodies be fitted the wrong way round or are they both the same. I know on certain models of Triumph the part no AUD 2140 is fitted to the carb near the rad and AUC 1310 near the bulkhead. I will check the numbers on mine tonight. I have worked at a plumbers merchants for 30 years now and understand how this should work. Not much to go wrong .
If there is an easy fix or I am missing something please let me know. It`s starting to drive me mad . Regards Paul

[pookie]

Have you checked the fuel pump pressure. Much beyond 2.5 lb is not good. Also are the float heights correct?

Salut!

Pookie

[arcturus]

Where exactly is the fuel coming from? Was it a complete refurb' from Burlen and how long ago? Have you lifted the float chamber caps to check float level and checked the float valves are not sticking but moving freely
Check out this useful site.
http://www.gowerlee.dircon.co.uk/Tips.htm#mixture

[Derek UK]

Both float chambers are the same AUC 1310, it's the bodies that are handed. Although you may have problems with rust and dirt, remove both filters and try it without. You can try removing the one between the pump and the cabs first and see how you get on. The valves in the pump rely on back pressure from the needle valve and having another restrictor in the circuit, the filter/s, can compromise how they work. Volvo never fitted any filters other than the screen in the pump.
If you have a rusty/dirty tank, clean it out properly or you'll always have problems. If by chance you have a Quinton Hazell QH pump, they are know to give too high a pressure. Some carbs cope with it, some don't. Adding an extra gasket either side of the spacer can sometimes help as it shortens the pump stroke a bit.

[paul staines]

Thanks for the replies. Bit dark when i got home so will leave until Saturday. Burlen Re furbed the carbs a couple of months ago. I did replace the fuel pump with a new one from Brookhouse. The large spacer/gasket has also been fitted. The float bowls are both the correct numbers. Thanks Derick for the part numbers. The car has run fine for the last 600 miles with both the paper inline fuel filters fitted so far. Do you still suggest removing the one fitted before the pump or do i just leave it. Only other thing i can think of is when i parked it up in the garage over Christmas for a couple of weeks it would not start. This was due to the garage being on an uphill slope and the fuel had evaporated. We sucked the fuel through ( by mouth ) and it fired up straight away. Backed the car back into garage . Next time i started the car i noticed the leak. Regards Paul

[paul staines]

Originally Posted by arcturus

Where exactly is the fuel coming from? Was it a complete refurb' from Burlen and how long ago? Have you lifted the float chamber caps to check float level and checked the float valves are not sticking but moving freely
Check out this useful site.
http://www.gowerlee.dircon.co.uk/Tips.htm#mixture

Hi the leak is coming from the overflow hole underneath the fuel inlet pipe. too dark to check when i got home . Will check on Saturday. Burlen returned carbs 600 miles ago. About 8 weeks. Many thanks Paul

[old fart]

Hi I've had this problem in the past and it has always been the float chamber needle valve,or a porous float not floating.I don't believe fuel pump pressure will cause this problem,because ,if you think about it,a Jaguar e-type for instance,which has an electric pump capable of giving enough fuel to do 150 mph,doesn't overflow when it's doing 40 mph does it?
Also I always have a filter fitted,and the only time they have given trouble is when they have become clogged up causing restricted flow and stopping the engine,not flooding.
Good luck,Andy.

[Ron Kwas]

Paul;

Do you know if new bowl valves were fitted when Carb were refurbed (I don't see where you mention it in thread, but maybe I overlooked it)...but I hope new valves are included as part of a refurb...this would be a big part of the answer...because in my experience, the two biggest factors leading to bowl overflowing are:

1. Nonsealing bowl-valve due to wear, or debris (or even fuelgum) holding it open...that is why I recommend a post fupu filter (even if Derek doesn't recommend this...normally we always agree, but apparently not here...but it is paramount to me to assure NO debris is being delivered to valve and bowl...EVER...so that debris is eliminated as a cause of overflow!)...and because of this susceptibility to debris, work on the fuel system must be performed with a high attention to cleanliness! Inspection of what remains in the bowl sump (on either side of the central out-port), after an overflow incident, may also give a clue to reason for overflow... I also prefer the Grose-Jet brand of bowl valves...these have a dual ball design with a round seat instead of a conical brass or rubber stylus in a round seat...it seems to me that a ball is better at seating (or even self-cleaning) and will rotate randomly to wear better. I have yet to see these leak personally, but I have seen reports where others have...(cause unreported).

2. Overflow due to elevated pressure overcoming the bowl valve. The bowl valve closes as a function of force provided by the float...which is not a lot (I haven't bothered making a scientific study of this to calculate it, or measuring it, but the mechanism seems to be susceptible to being overcome by elevated pressure in the feedpipe and this is obviously generated by the pump. Installing replacement (or electric) pumps which put out a lot more pressure often results in bowl overflows...unfortunately, the typical low pressure fuel regulators which are available are low quality rubbish which seldom (if ever) work as they should. I have no answers or recommendations here...just a warning to beware when fitting replacement fupus!

Additional Considerations:

Vibration. I don't know how much of a factor this is, but we shouldn't discount it...Webers have anti-vibration mounts, so they clearly recognized it as an issue.

Heat. I don't think this is a contributor here.

That's all I can come up with at the moment...Good Hunting!

[Burdekin]

Also a couple of other things to check, check that the float heights are correct and therefore turning off the incoming fuel. Press down on the needle valves and blow through and see if they are working.

[222s]

Originally Posted by Ron Kwas

Vibration. I don't know how much of a factor this is, but we shouldn't discount it...Webers have anti-vibration mounts, so they clearly recognized it as an issue.

This theory gets my vote. When dealing with similar issues in the past on my car, I found that this was the problem after repeatedly cleaning and changing parts in the float chambers... It was eventually solved partly by minor tweaks to the carb settings to get it running smoother, in particular making sure that the idle wasn't set at a particular speed that always seemed to trigger the leaks from the overflows. No idea what rpm that was though as I don't have a tacho.