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MG MGB Technical - Better float needles?
|I've just put my roadster back on the road after a lengthy layup and I've encountered a familiar problem, the carbs are overflowing occasionally [HIFs] at tickover, over the years I've replaced the float needles a couple of times but they never seem to last, does anyone in the UK supply a better valve.|
|Are you sure the float is free of petrol? I had two or three bouts of this over the years on my V8 HIFs, changing the float valves semed to fix it for a while, until the last time. It was only then I noticed the float contained some fuel, I could not locate the hole by shaking, squeezing or warming so it must have been minute. It's been fine since replacing that. One bad float valve I can understand, possibly two from the same batch if bought from the same place a short time apart. But normally they are fine, and reputedly better than the mis-named Grose 'jets' that are often mentioned. But if it is happening to *both* carbs then I'd suspect dirty fuel, do you have a filter? If so I'd replace it. I agree with you they are a pain to replace, unlike HSs. Do they overflow if the ignition is left on with the engine stopped (disconnect the coil)? The SU pump should not click more than once every 30 secs like this. Another test is to disconnect the pump and run the carbs dry, then reconnect the pump. The resultant rush of fuel through the wide-open valve can clear any debris, if it happens again immediately then either very dirty fuel or a sunk float or a bad valve, if it only happens again after some time then more likely to be slightly dirty fuel. If it *is* only when idling then vibration is a possible cause, and with the rigid-mounted float chambers of the HIF as opposed to the rubber-mounted ones of the HS I'm not sure what to do about it. However overflow at idle is *not* a common problem, so there must be something wrong with your setup somewhere.|
|Paul Hunt 2|
|SU carbs are designed to operate with fuel supplied at 3-4 p.s.i. (low pressure)|
If you have replaced the fuel pump with one that operates at a higher pressure, that may cause the problem.
Otherwise, I'd check the needle valves for dirt, etc.
|Ron, if you have needles with metal tips, try and get some that have the Viton rubber tips, I have had great success with these. In the US Joe Curto carries them.|
|Thanks for the replies, I'm beginning to think the problem might be with the petrol pump, it's an electronic one which might be too strong for the needles. I've got one of these glass filters which looks clean and the last time I replaced the needles [a couple of years ago] the floats were OK then. I've now done about 50 miles and it seems to be settling down, so maybe it didn't like being ignored for the last 18 months!|
|GROSE JET No 12 here:|
I think people have mixed results from these though.
I'm using a weber now though.
|I found my GT has an aftermarket fuel pump when the float valves failed. I bought a pressure regulator from filter king, which, set to 2 psi, solved that problem and has the added benefit of period looks with a nice glass bowl filter element.|
From experience with my (dead) roadster, I don't think groose jets are any superior to not worn factory standard.
|I've never actually seen Grose jets, what's the difference between them and standard ones? there doesn't seem to be much difference on price.|
A Grose "jet" (as Paul rightly points out, it's not a jet but rather a valve) uses two ball bearings to check the flow of fuel. A large ball sits in the end of the body (visible in Michel's photo). When the float rises, this ball presses against a smaller ball, which in turn sits in a cup inside the body and thus shuts off the fuel.
It is claimed by the manufacturer that this design is more tolerant of dirt than the standard needle and seat. It is claimed by consumers that this design is LESS tolerant of dirt than the standard design. FWIW, I ran a pair for 10 years before one finally failed. I replaced both with standard viton-tipped needle valves.....
|I had the Viton tipped needles in for a while but have now fitted a fuel pressure regulator and gone back to the originals.|
|Having now read a bit more about Grose jets, it seems some people swear by them and some swear at them, so I've ordered a nice pressure regulator and filter by Filterking, as Paul says there must be something wrong with my set up I've changed the float needles 3 times in the last 10 years, they can't all be bad.|
|I forgot the possibility of an after-market pump, but if yours is of the electronic SU type then I doubt a pressure regulator will make any difference. If from another manufacturer then almost certainly it will.|
|Paul Hunt 2|
|Fingers crossed, the Filterking seems to be working, I've now done about 200 miles without problems and an occasional slight hesitation on acceleration when hot has disappeared as well.|
Paul, I'm pretty sure it isn't an SU electronic type, I fitted it about 10 years ago but can't remember what make it was?
This thread was discussed between 27/02/2006 and 05/03/2006
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