SU Carbs

[geonecro]

Hi everyone

 

I posted some time ago about a problem I am having with my HS6 Carbs, I have tried the suggested cures but still have the problem, the rear Carb overflows down the overflow tube when it feels like it.

I have tried 3 new needle valves, new grose valve, I have fittted rubber mountings (stop vibrating valve off seat), I have fitted a heat shield (fuel and carbs now nice and cool), the pressure on my fuel regulator is turned down very low, and I have even tried washers under the valve to lower jet and fuel level, and it has plastic float which can not be adjusted.

The carb still overflows, sometimes as soon as you turn on, sometimes after its been ticking over for 5 mins and sometimes after a run the only guarenteed thing is that it will overflow at some stage during a trip out. Does anyone else have any ideas as Im stumped?

[jonlar]

Hi David, only thing I can think of, have you tried comparing the weights of the floats/ or tried swapping them over and see if the problem moves with the float, it's very unlikely, but could the rear one be too heavy and sitting too low..............grasping at straws!

[marvmul]

Perhaps the plastic float is sticking? The upper side of the float , where the needle is making contact and sliding over the float, can be knackered, or the pin can be sticking.

[graeme]

Hi David,

 

Check the plastic float has no holes in it, as it will not float if it fills with petrol and therefore not shutting the valve.

 

Graeme

[Guest nco]

HI David,

 

I once had an old mini that had a similar problem - it turned out to be the cut off valve in the float chamber not sealing.  It caused excess fuel to be fed into the float chamber and then flooded the carb.  There is a little valve operated by the float mechanism.  From what I recollect about 10mm long, tubular and tapered to a point at the end.  It didnt look worn other than a ring of brighter brass where it was meant to be sealing.  It was enough to stop it working though.

 

Leaky floats obvious - full of petrol!  My bet is its the little valve controlled by the float is your problem!

 

Neil

[P.J]

Hi Folks,

 

Just joined the forum and was checking out some old posts and noticed this one and think I have the solution.

 

I had the exact same problem on my TR6 with twin HS6 SU. It took me an age to figure it out, I did all the same things and ended up with grose valves but still it did not cure the problem. It turned out not to be the valve not closing but the float not closing the valve.....the floats were replacement white plastic ones and they had a small square tab coming off the rim behind the pivot point, it looked like there was bags of clearance with the side of the chamber but in desparation filed it down a touch - the problem was cured instantly and has never re-surfaced.

 

Best Regards.

[Guest ron]

I recently bought a pair of float needle valves from Burlen for the HIF SUs in my MG, they have redesigned them quite a bit and they now incorporate a very small filter, don't know if they have done the same with the HS6 SUs but it looks as if they might be acknowledging there has been a problem with the old design?

The float in the HIF can be tweaked slightly to ensure that the valve actually shuts properly, presumably you can do this with an H6 as well, at least the HS6 floats chambers are easily accessible, on the HIFs the carbs need to come off the car every time an adjustment or needle replacement is needed.

Ron

Edited March 7, 2007 by ron