SU Slopers

 
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John Murch



Joined: 05 Jun 1976
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I have been a bit concerned that my 3Ltr was running too rich, today I went to a rolling road to really find out what was happening.
The results were most interesting. It was running rich at idle and very much worse at 3300rpm (where it recorded 75hp at the flywheel - not very impressive!), these were full throttle figures, it ran even richer on part throttle.
With the jets adjusted to the leanest possible setting it was still rich at idle - surely at this setting it shouldn't run at all, something is not right!
An investigation into needles, jets float levels etc. is now called for, this certainly accounts for my poor fuel consumption and bad performance above 1500mts.
Any suggestions as to a Sloper expert - Burlen Services?
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Stephen Blakey



Joined: 02 Feb 1995
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The richness is likely to come from wear in the needles and jets plus possible loss of buoyancy in the floats and it sounds from your post that you're on to this already. It's a while since I looked inside an SU. Is the float height adjustable?

I picked up the Burlen catalogue at Race Retro. They do list the 3L and slopers get a mention so they're worth phoning (01722 412500). As Chris may confirm, a lot of the reproduction stuff is of very dubious quality so keep your suspicious hat on.

You will certainly get improved economy from sorting this out but, unless it is going into rich-misfire, the change in power will be small. The surplus fuel vapour will be displacing a small amount of air, but not much. Still, every little helps!

You can get various devices for monitoring AFR, including a gauge for (discretely hiding behind) the dashboard. This might save you repeated trips to the rolling road.

Do let us know how you get on.
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John Murch



Joined: 05 Jun 1976
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Thanks Stephen,

The points you mention are all the ones that I'm thinking about.

I've just had a helpful chat to Burlen Services. The float hight can be adjusted, with the aid of a soldering iron. How to do this is also in the TF's.

There seem to be quite a few areas on these carbs that can be problematical, so I might fit a pair of HD6's (with a different manifold) for the medium term, which should cure my problems. I would keep the G5's which could be easily refitted in the future.

I like the idea of the monitoring device and will research that as well.

I am not that concerned about ultimate power, although I would like it to perform as well as it should. What concerns me with the rich running, is the possibility of accelerated wear caused be an excess of fuel washing the oil off the bores.

john
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Stephen Blakey



Joined: 02 Feb 1995
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This is one way of doing it

http://www.demon-tweeks.co.uk/motorsport/gauges-auxiliary/stack-wideband-lambda-gauge

You'd need to fit a lambda boss, which Demon Tweeks may also be able to supply. There are loads on Ebay e.g.

http://www.ebay.co.uk/itm/Exhaust-Lambda-Boss-Nut-and-Plug-Bolt-M18-x-1-5-Oxygen-Sensor-Mild-Steel-/110873769303?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item19d0977557

Of course, others may know of cheaper ways of doing this.

I think you're right to be concerned about bore-washing. Also, it would be good to reduce fuel usage generally as I am planning on driving my Bentley to the club's centenary and I'm worried there won't be any fuel left by then, particularly since I distinctly remember reading on here that the entire population of China will soon be driving GTC's.
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Christopher Carnley



Joined: 16 Nov 2007
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John,

I was going to suggest, rather tentatively, a pair of HIF S.U,s for the points mentioned,as bore wash and ring/groove corrosion has to be seen to be believed.

Originality is alright to look at, but slopers have always been a NO NO for me.

Chris.
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Dan Suskin



Joined: 22 Feb 2011
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Stephen Blakey



Joined: 02 Feb 1995
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Dan,

Thanks for that. Does yours look like this?

http://www.efi-parts.co.uk/index.php?productID=237

They also have a cheaper one.

http://www.efi-parts.co.uk/index.php?productID=204

It seems many use the same Bosch LSU 4.2 7057 sensor.

Best wishes,

Stephen
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Robert Craven



Joined: 09 Apr 2004
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John,
Where was the rolling road you used? Were they knowledgeable about vintage cars?
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John Murch



Joined: 05 Jun 1976
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Hello Robert,

I hope your car is all back together and running well.

I went to http://www.northamptonmotorsport.com/

They have done quite a number of Bentley's but I think I was the first set of slopers. They were not able to get the 'top' off the carb to access the needle (it had been put together with some sort of sealer, and they didn't want to damage anything) so were not able to check the condition of the jet and needle.

Paul Spencer came with me to Northampton, he knows of another Rolling Road in Somerset that might have greater experience with vintage cars. However I think it unlikely that even they would carry stocks of alternative jets and needles for G5's (or perhaps they are common with other models?)

I have had a look at the various Air/Fuel ratio meters suggested below, lots to think about!

The rolling road people used one that was inserted into the tailpipe, the lambVt results are clearly of different 'type' to the output of some units. But it told me what I wanted to know, namely that the mixture was all wrong and very close to a rich misfire and (probably) as a result well down on power and torque. If anyone is interested I could scan the graph and email it.
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Dan Suskin



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Robert Craven



Joined: 09 Apr 2004
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John,
Thanks for inquiring about my car. I'm sorry to say it's not ready yet, but I hope it won't be long/
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Stephen Blakey



Joined: 02 Feb 1995
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Location: Derbyshire, United Kingdom

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Dan Suskin wrote:
Stephen

I went with this one:
http://www.zeitronix.com/Products/dashdaq/dashdaq.shtml

It is very customizable (not sure if that's a word or not), has a built in GPS, and I can just hide it away when not in use.


Hi Dan,

If you can have winningest, then customizable's a given.

That looks like a fantastic piece of kit. I had a brief period working on EFI in the early/mid 80's. In those days a data logger was the size of a fridge and had very limited memory. To get it in a test car you either had to remove the passenger seat or try and strap it to the rear seat somehow. The idea that you could get hours of data on something the size of a postage stamp would have seemed incredible at the time.

It would be helpful if you could give us some indication of the sort of AFR's you're seeing. Do they conform to the text-book settings of going a bit lean at part load and a bit rich at high load? This was described to me by my boss at Weslake as using all the fuel at part load and all the air at full load. There's a lot more to it than that of course. I think he was trying to make it easy for me.

Best wishes,

Stephen
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Dan Suskin



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John Murch



Joined: 05 Jun 1976
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The AFR's on my car varied from 10 to 12.8 at full throttle and were worse at part throttle.
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John Murch



Joined: 05 Jun 1976
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After some intensive research and listening to a number of knowledgeable people, I have decided to go with a pair of HD4 SU's. The general consensus is that while a 3ltr will run well on HD6's one should get slightly better results with the smaller units. The main reason for this (if I understand the advice given correctly) is that the smaller throats will give higher air velocity resulting in better atomization.
In due course I'll put it on the rolling road and see if things are improved.
Thanks for all your comments and advice.

Edited: an error in the above, it's H4's I'm fitting not HD4's


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Dan Suskin



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John Murch



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Dan, yes I would have thought it could. I do not know if other needles are available for the G5's (or are needles common to many models?) I'm sure a skilled person could make one - which rules me out.
I shall be keeping the slopers and rebuilding them in due course. But I don't believe that they will ever be as efficient as the later models.
One of my prime reasons for doing the change is to improve the ecconomy and thus the range. I could have had a bigger fuel tank, but the reality of the costs of this put me off.
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Laurie Fox
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John

Burlen would know whether needles are special to a particular carburettor or not.

Laurie
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Robert Craven



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Burlen have certainly stocked the needles in the past and I imagine they still do. The spares scheme also lists them. I think there are three kinds for slopers: weak, normal and rich. My notes say (but I'm not sure where I got them from) that normal is CV (Burlen no. AUD 1112) and weak is BC (Burlen AUD 1063).

I think you'd need the skills of a watchmaker to make your own.

PS I've found where I got some of the above from: page 29 of the Technical Facts. But I can't find the needles on Burlen's website, though I know I once bought some from them.
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John Murch



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Thank you Robert for that most important information, I had asked Burlen for these details but the person I spoke to was rather vague about it! When I come to rebuild the slopers it will be interesting to see what is in there at present and the state of the needles and jets. Burlen did say that the fuel flow is remarkably abrasive.

(why did I not spot the info in TF's!)
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Paul Spencer



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I love it when these threads lead to interesting facts. For example, now I know (from the Burlen web site) that SU stands for "Skinners Union" after the founders. Also, the reason for sloping the suction chamber and needle assembly was to reduce the fluctuations of the chamber when driving over the rough, unmetaled, roads of the period. Perhaps the disadvantages outweighed the advantages as it didn't seem to catch on.
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Dan Suskin



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Stephen Blakey



Joined: 02 Feb 1995
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There's a brief explanation of SU nomenclature here;

http://answers.yahoo.com/question/index?qid=20081113051731AAi7oHe

John,

1½" SUs were good for 95 BHP+ on the MGB. I'm inclined to agree that you should get better metering and driveability with these than the 1¾".

The owner of the aspiration referred to elsewhere has ordered a two-channel AFR meter; one EGO for each bank. You could perhaps do with something like that with one sensor for each carb. I saw a W.O. at Silverstone last year that had 4 Lambda nuts in the manifold; one opposite each exhaust port. Somebody obviously wanted to know precisely what was happening. You can get significant AFR variations between cylinders that are fed by the same carburettor, however that may be the least of your worries.

Do keep us informed
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Stephen Blakey



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I came across this photograph whilst looking for something else. This was in the trade marquee at the concours in 2011.

It doesn't say what model H6's they are, presumably off a jag of some sort. Maybe an SU expert could enlighten us. They look a bit big for a 3L, though I appreciate there are more scientific ways of choosing carburettors than by appearance.
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Stephen Blakey



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Here is the dual channel AFR which has been ordered for the aspiration mentioned elsewhere;

http://www.grahamgoode.com/innovate/new/inn3807.html

It's got data logging and all that. I'm not sure it's worth three times as much as the simplest single channel round dial type, which could be hidden behind, say, a clock face to be flipped out, James Bond fashion, when you need an AFR readout.

Anyway, I'm looking forward to playing with it and will report back in due course.

I'm intrigued by the engineering challenges posed by the H6 conversion. The cheapest way of mounting them might be with adaptor plates but making the linkages work may not be trivial. There are cable-operated versions of the carbs, of course, however they might be a bit nasty in such hallowed surroundings.
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Christopher Carnley



Joined: 16 Nov 2007
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You are so right, and a rubber piped push on fuel feed!?

You should see the results of the RG return, the 1/2 thickness thrust washer
was held on with a Seeger (spring) clip!

Not surprising it kept disengaging.

Chris.
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Robert Craven



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I have now had my 3 litre back after extensive repairs following my accident over a year ago. I'm delighted to have it again and very pleased with the work, but it soon developed a problem probably unconnected with the accident (except perhaps the fact that the car hadn't run for over a year). I had entered the Pembrey sprint (my one local event) in anticipation of having the car back, but it ran very badly and I was very slow.

At first I thought it was a faulty magneto, but I now think it was carburation. All the plugs were very sooty and the front carburetter (to adopt the SU Sloper spelling) was too rich at idle however much I adjusted it. The needle was within 1 thou of its specified size according to my micrometer. The problem seems to have been the jet and in particular the cork seals. I replaced the seals (and the jet, as a precaution) with a kit from Burlen (after soaking the seals in oil for 24 hours, as instructed). The new seals were very much larger than the shrunken old ones, but they still fitted.
This seems to have done the trick and I can now adjust the mixture from lean to rich. I think the explanation is that with faulty seals petrol can leak past the jet and enrich the mixture regardless of how the jet is adjusted.

PS the jet kit I got from Burlen contained new upper and lower jet bearings. One was longer than the original and the other shorter, though the combined effect was less than 1 mm longer. I decided not to risk creating another problem by using them. Maybe I'll try fitting them in the future.
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Robert Clifford-Wing



Joined: 10 Nov 2015
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I have just returned from having our 3 litre slopers looked at. Rolling road tests revealed lean mixtures at high revs under load but rich at tick over. Inspection revealed very worn jets which were replaced. The carburettors fitted were for a 4 or 4.5 litre engine, there was insufficient demand from the engine to fully lift the Pistons. New needles were fitted and machined to deliver correct mixtures up to 3500 rpm.

The car now performs much better, being smoother running and delivering more power under load at all speeds. I await better fuel consumption figures maybe?

I used Sigma Engineering in Gillingham Dorset (01747 823270) and was well received and looked after by the proprietor, an elderly gent with masses of experience in restoring older cars etc.

Highly recommended
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John Murch



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Rob, glad that you have the carbs sorted now, thanks for the recommendation.

My foray into H4 carbs was a total waste of time, there was no change in fuel consumption or performance. (17mpg regardless of how driven). I am back on the slopers.

John
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Robert Clifford-Wing



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John Murch wrote:
Rob, glad that you have the carbs sorted now, thanks for the recommendation.

My foray into H4 carbs was a total waste of time, there was no change in fuel consumption or performance. (17mpg regardless of how driven). I am back on the slopers.

John

Before adjustment I was returning 19/20 mpg but in fairness the power loss at mid range was limiting output. I look forward with interest to consumption figures over the coming weeks.

Are there G4's around ever and would my H5's be of use to others if I decided to replace them? Having said that, the performance is much improved.
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Robert Craven



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Rob, sorry if I'm being obtuse, but are you running on Slopers (which are G5 - I don't think there was a G4) or upright H5's ?

Machining your needles sounds quite adventurous, though I know it can be done with care. But if they were ever to wear and need replacing you'd need to repeat the process rather than knowing what to choose from the pretty extensive off-the-shelf range.

PS If you do want to choose from the existing range you can play around with this site: http://www.mintylamb.co.uk/suneedle/
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Robert Clifford-Wing



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Robert Craven wrote:
Rob, sorry if I'm being obtuse, but are you running on Slopers (which are G5 - I don't think there was a G4) or upright H5's ?

Machining your needles sounds quite adventurous, though I know it can be done with care. But if they were ever to wear and need replacing you'd need to repeat the process rather than knowing what to choose from the pretty extensive off-the-shelf range.

PS If you do want to choose from the existing range you can play around with this site: http://www.mintylamb.co.uk/suneedle/


Sorry Robert the car is 20 miles away so I can't check the markings but, they are slopers and not G5 but start with an H, maybe HU5. Either way they are too big for the 3litre as the engine will not fully lift the pistons, hence the reason for machining two needles ( can't remember what no: they were but I was told they were a speck for these carbs'. The taper was shortened of or made steeper to allow for reduced piston lift and to deliver correct mixture.

The above must sound an amateur description, which it is! The results were a much improved and smoother engine and a more even power output. Take your point about the needles but with oversized carbs' there wasn't much choice, so I was told. The magnetos were unevenly timed and too far advanced so that adjustment helped greatly too.
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John Murch



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As Robert says, Slopers are G5 and were also fitted to 4.5 cars before they went over to HV5. HVG5 fitted to the Blowers and I think the Speed six and 4ltr.
[img]
Photo of G5.
The HV5 is a more normal vertical looking item.[/img]
The throat size would be the same, I have a full kit for fitting the H4, complete with suitable manifold. You would be welcome to try them out, but if you are running well now with the HV5's I wouldn't change them.
Edited
I used the wrong word above, it is the bore size that is the same, the throat size on the versions used on the 4.5 is bigger.
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John Murch



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[img]
I think these are HV5[/img]
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Paul Spencer



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John - your engine is far too shiny. You are showing the rest of us up.
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Robert Clifford-Wing



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See the images attached of the carburettors fitted to the car. Any thoughts?
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John Murch



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Paul Spencer wrote:
John - your engine is far too shiny. You are showing the rest of us up.

Paul, that was 12 years ago, it doesn't look like that now!

Rob, you have G5 units, but at some point either the float chambers and/or the lids have been changed for parts from the HV5's.
John
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Robert Craven



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Rob, the first thing that occurs to me is you should be careful not to let your thumb nuts shake off. I've lost a few and I now lock wire them.

As John says you seem to have a combination of G5 Sloper carbs and HV5 float lids and/or float chambers. I'm not sure why what look basically like G5 Slopers are said to be too big. According to the Technical Facts G5 Slopers are 1 5/8" diameter. Perhaps what's wrong is the air suction hole to the piston chamber. See section 1.14 note 2 of the TFs.
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Chris Card
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A useful test you can do, is, with your fingers, block off the air holes in the front of the body, below the piston chamber (just behind the front fixing screw), lift the pistons and then see if they fall at roughly the same rate as each other.

If one falls much faster than the other (they're unlikely to be exactly equal), then there is more wear in that barrel, and the pistons will not lift equally under suction. This, in turn, means that the carbs will never be in balance under running conditions.

I don't know if this can be fixed, but someone like William Medcalf is bound to know the answer.

Chris
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Robert Clifford-Wing



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Chris Card wrote:
A useful test you can do, is, with your fingers, block off the air holes in the front of the body, below the piston chamber (just behind the front fixing screw), lift the pistons and then see if they fall at roughly the same rate as each other.

If one falls much faster than the other (they're unlikely to be exactly equal), then there is more wear in that barrel, and the pistons will not lift equally under suction. This, in turn, means that the carbs will never be in balance under running conditions.

I don't know if this can be fixed, but someone like William Medcalf is bound to know the answer.

Chris

So, to be clear, are there only G5 slopers or were there other sizes made?
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Robert Craven



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According to the recently published history of Skinner's Union ("SU") there were G2 and TX versions of Sloper carburreters. I haven't noticed any reference to any other sizes or versions, other than G5.
Duff used SU carburetters in the 1923 Le Mans. I think it's usually assumed he used G5s, but as far as I've noticed the book doesn't expressly say this and I wonder whether they'd actually started making G5s in 1923.
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Robert Craven



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As to Chris's point about wear in the barrel I suppose you could make an oversize piston or even plate the piston with something, but I suppose like with an engine block you'd find the barrel hadn't worn evenly and you'd have to bore it out and end up doing no end of work.

Last edited by Robert Craven on Thu Jan 21, 2016 10:47 pm; edited 1 time in total
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John Murch



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I don't think that the piston should ever go quite to the top of its travel, perhaps 3 or 4mm off.
If it is way off in its travel, you could lighten the piston, is the housing clean and the oil not too viscous?
Regarding smaller sizes of slopers, I believe these may have been fitted to some Wolseley and Rover cars.
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Chris Card
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Following on from John's point, the barrel should be clean and not over oiled - too much oil will result in sluggish response.

If you lift the piston and then let it free fall, it should seat with an audible click.

Chris
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Paul Spencer



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I know mine fall at different rates but I have ignored it on the basis that the car goes well and I don't know how to fix it other than a new carb.
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Chris Card
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Paul - because there are so many other variables in the "breathing", I think the difference has to be significant before you would notice it when driving.

Chris
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John Murch



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Robert Craven wrote:
According to the recently published history of Skinner's Union ("SU") there were G2 and TX versions of Sloper carburreters. I haven't noticed any reference to any other sizes or versions, other than G5.
Duff used SU carburetters in the 1923 Le Mans. I think it's usually assumed he used G5s, but as far as I've noticed the book doesn't expressly say this and I wonder whether they'd actually started making G5s in 1923.


I was also curious as to when G5 's were first made. So have had a trawl through my Bentley books. In Clare Hay's book on Ch. 141 (the Duff Le Mans car) it says that through out the car's racing life it was fitted with a 'racing Claudel-Hobson carburettor' and that this was only changed to G5's by a subsequent owner.

In the 1923 Coupe George Boillot event in September 1923, Duff entered in 141 and Clement in 246, it is stated that 246 was fitted with twin Claudel Hobson units, and the inference is that 141 was fitted with a single.

So my view is that G5's were not available (or perhaps untried?) in September 1923.

john
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Robert Craven



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In my earlier post on Duff using SUs I was relying on the new book on the history of Skinner's Union. On page 69 it refers to two letters Duff sent to the SU company in 1923. In one before the Le Mans race he said he'd been testing "an SU carburetter" and in one written after the race he wrote praising their "most excellent carburetter" and describing how well the car had run, and the company used these letters in its adverts in 1923.

No details are given of what kind of SU was referred to.

The book also seems to indicate that the company adapted their carburetters to suit particular cars. It says they introduced what became known as the Sloper in 1921, but in fact the book contains earlier pictures / diagrams of what might be described as sloping style carburetters.


Last edited by Robert Craven on Sun Jan 24, 2016 2:53 pm; edited 1 time in total
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John Murch



Joined: 05 Jun 1976
Posts: 1567
Location: London, United Kingdom

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Robert, how fascinating, I havn't seen the Skinners Union book and obviously Caire Hay hadn't been aware of those letters. So perhaps Duff was using G5's or a pre production version.
In none of my books have I been able to find a photo of the engine of the Duff car.

John
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Robert Craven



Joined: 09 Apr 2004
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John, I too haven't found a photo of the engine of the car. I wonder what Hay says in her new book.

PS, I wish this forum had a spellchecker built in to it. I often spot mistakes in my posts some time after I've sent them. I think Firefox may once have had this feature, but if it did it seems to have gone from my computer.

PPS I've got it working again now.
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John Murch



Joined: 05 Jun 1976
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Had a look in the latest 'The Vintage Years' - for ch 141 Clare states 'Dec '23 SU Carb fitted, Jan '26 Twin SU's fitted. - and for 246 1923 model front wheel brakes, twin SU carburettors.
Not sure what was fitted for the 1923 Le Mans now!

I switched off my spell checker as it would change complete words, with rubbish as a result. Now you just get my bad spelling!
John
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Robert Craven



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It's notable that in his letters to the SU company Duff uses the singular word "carburetter".
But whichever chassis he drove, the Le Mans race was in May 1923.
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