MarkB Posted September 10, 2012 Share Posted September 10, 2012 Hi AllI rebuilt a set of HS4 carbs a year or so ago and fitted them to my Mk3 Spit. I had a problem when on occasion the front carb would start to leak fuel out of the overflow pin hole on the lid of the float chamber. This had a new needle valve assembly fitted that came with the comprehensive SU overhaul kit. I remember on some of the earlier SU's there was a tab you could bend to set the height at which the float acted on the needle valve to shut off the fuel. The valve is working when i blow through it and I have replaced the float incase it had lost some of it's buoyancy. There is no means that I can see of setting the float height on these carbs other than putting a fibre /copper spacer washer on to of the brass needle valve holder before fitting it to the lid of the float chamber. This should have the effect of shortening the movement of the float before it presses on the valve shutting the supply. Any ideas?Mark Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted September 10, 2012 Share Posted September 10, 2012 Yes, float height is set by different thickness washers under the neede valve. PITA!Fuel pressure is also important. SUs prefer around 2psi only. Many pumps supplied today are more like 4 - 5psi.Nick Quote Link to comment Share on other sites More sharing options...
MarkB Posted September 10, 2012 Author Share Posted September 10, 2012 Thanks Nick.I'll have to have a look at what washers I can find. The one thing I didn't get in the "comprehensive kit". Yes, going to be a bit hit and miss I think. I did think about fuel pressure as I recently fitted a new pump from Canley's but I rate there stuff so I think that should be OK. Also I had cheeks like a glass blower when trying to force air past the valve. I have been trying to get back working on my Vitesse rebuild for the past 6 months, but have been side tracked with MOT's and various problems On the Spit, GT6, Van Motorbike, car, car trailer (that I use once every three year's or so) something has got to go!Cheers Mark Quote Link to comment Share on other sites More sharing options...
Chasj Posted September 10, 2012 Share Posted September 10, 2012 Hi.Only a thought having had a similar flooding problem on my Mk.IV Spitfire.The first occasions were cured by new needle valves so fair enough.Later on I got more problems and found tiny bits of black in the inline filter and float chambers. Removing and blowing through the valve cured things for a short time. I then found the throw away inline fuel filter was being dissolved. I was using Tesco 99 octane fuel and on investigation found they achieved this rating by increasing the bio levels beyond 5%.Changing to BP 97 octane, a new glass cleanable filter and a couple of tanks later no more problems.Charles. Quote Link to comment Share on other sites More sharing options...
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