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TOPIC: Carburettor Query

Carburettor Query 4 months 3 weeks ago #859

  • Batten
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Dear All

I was looking at my HC4 Carb the other day and I noticed that the connecting flange is not parallel!

It appears that the current flange connection is angled so that the carb is angled about 10 degrees down and 3 degrees to the left. First thought was, that like so much of my machine, somebody may have "adjusted" the flange for some reason. However, I am pleased to say that this doesn't seem to be the case. So dose anybody have any ideas why this may have been done?

Below are some picture to illustrate the query and in particular picture #2 shows the carb flange face which has the same plated finish as the rest of the carb and no obvious home adjustment marks.

Thanks

Phil
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Last Edit: 3 months 3 weeks ago by gioorl.
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Carburettor Query 3 months 3 weeks ago #874

  • Peter Gillespie
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Hi Phil
I dont see any pictures.
I have made new stainless steel float bowl retaining springs and I have a few spare if anyone needs them.
I also have a few return springs
Regards
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Carburettor Query 3 months 3 weeks ago #877

  • Batten
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Hi Peter

Hopefully, the missing pictures are attached now.





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Carburettor Query 3 months 3 weeks ago #878

  • Alan
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Hi Peter,
I hesitate to respond as you have already helped me out with spindle lock washers and other bits, but I was looking at my HC4 last week and wondering how I could get a bowl retaining Spring made - one is ok but the other is a bodged replacement which is too short. By magic your post appeared the following day.
I’d be very grateful to get one of yours, preferably on a payment basis.

Alan
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Carburettor Query 3 months 3 weeks ago #880

  • Peter Gillespie
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Hi Phil
I have looked at all my Claudel Hobson carbs and the flanges all appear to be parallel. Has your inlet manifold been repaired and perhaps modified?
While we are on the inlet manifold ,as you all know the manifold has the heating pipes passing through the inlet manifold. After time the manifold corrodes through either creating a leak into the manifold or through the housing to atmosphere.If there is a leak into the manifold it makes the carburetor impossible to tune.
I have pressure tested all my inlet manifolds and found them all to leak . Four of the manifolds have previously been repaired and one is still original and unmolested.
The inlet manifold tube has 1 mm (40 thou) wall thickness and it is a piece of art. The repaired manifolds are a mess.
I was thinking of looking into making new parts for the manifold including upper and lower pressings of the heating chamber or perhaps a whole complete manifold.The way I go forward will depend on the demand for this. So to steal Alex`s words " Hands up Please if you are interested".
BTW the spare Stainless Steel float bowl retaining springs have all been claimed by members and if we will need more we will have to make more.
Regards
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Carburettor Query 3 months 3 weeks ago #881

  • Batten
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Hello Peter

I don't think the carb has been modified. The reason I say this is that the sealing face is flat in both planes with no obvious saw marks and the finish nickel (?) plate as the rest of the carb. I can understand the carbs slight bias to one side, which could be to provide an even fuel mix to both cylinders. However, droop of the carb towards the gearbox seems to be a bit counter intuitive to me. I am going to try it when the rest of the engine is back together, but I may have to fit some sort of bias gasket to correct the issue.

Thanks the info on the inlet manifold. Once I had stripped the paint off mine I did look to see if there was a clear passage across it for the exhaust heating gases. Mine appears to be blocked, which from what you have said might be a good thing!
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Carburettor Query 3 months 3 weeks ago #882

  • Paul
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In response to Phil's dogeared carburettor flange, I suspect that it came as an attempt to compensate for a sadly-repaired inlet manifold, or to adapt it to a non-ABC machine...notwithstanding the surface finish.
Partly on this theme, yet another carb. that I came across featured a hacked-out port-side flange hole. When I remarked on this to Keith, he said, They are ALL like that! It was a factory mod. to enable carb. removal without disturbing the electric-control gear just aft of the carb., or the inlet manifold in front. I wonder if C-H was ever requested to modify their flange design, to stop the Sopwith factory hacking.
On the subject of inlet manifolds, you are referred to Chapter 3 of my 'Learn Your ABC' series of short articles that appeared in the VMCC Journal in 2013: in this instance, the March issue. Peter is a perfectionist producer of replica ABC components to a very high quality, but in this case, although I marvel at his achievements, I hope he deviates from the aircraft-quality steel tube and sheet used in the originals, to stainless steel!
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Carburettor Query 3 months 3 weeks ago #883

  • keithsams
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what i actually said was
all the carburettors have the cut out,i dont know if sopwith did it or hobson but having looked at them again they were not all good jobs so it was probably sopwith.
if you have lights fitted the blowback on the end of the carb. is very close to the eletrical control box and if you need to removed the carb. for say a bloked jet that they often did you had to remove the box to remove the carb.
with the cutout you just slacken the nuts off swivel the carb. around and take the main jet out.
i dont have that problem i have fitted an inline petrol filter.i once did a run before i fitted the filter had a blocked jet forgot my spanners and had to walk back to the start(4 miles)
what is the serial number of your carb. it should be in the 20000s also has it been bored out the speed men did this,from around 15mm up to 20mm.paul may have a point about being off another bike but still dont know why it is cut that way,i think we have a long way to on this one.
was the carb. cut to make it better for hillclimbs ?but its the wrong way ?
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Carburettor Query 3 months 3 weeks ago #884

  • Peter Gillespie
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Hi Paul, If we get to the stage of manufacture we will try and engineer out the problem. Stainless steel will be a solution.
Your articles " Learn Your ABC" that was published in the VMCC Journal, is there any reason why the article is not on this website? If there is no reason Please would you publish them here. Have I missed them somewhere?
If anyone has an old or leaking manifold please let me know as this will help in the decision on the best way forward.I think, if there are enough leaking manifolds it may be worth our while to only reproduce the heater section out of something that will last long. The original Sopwith bends with their light flanges and spotface are beautiful and I would hate to loose them.
Regards
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Carburettor Query 3 months 3 weeks ago #885

  • Batten
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Hi Keith

The serial number on my carb is 26915 and has a 15mm bore venturi. Apart from the mounting flange the carb looks fairly standard and un-molested. What other bikes used the HC4 carb? I would be interested to see how other machines might have mounted the carb.

Also I have pressure tested my inlet manifold with a bike pump and I am pleased to confirm that I have no leaks. I think I might paint it now.

Phil
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