Carburettor Query

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4 years 2 weeks ago #882 by Paul
Replied by Paul on topic Carburettor Query
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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4 years 2 weeks ago #883 by keithsams
Replied by keithsams on topic Carburettor Query
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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4 years 2 weeks ago #884 by Peter Gillespie
Replied by Peter Gillespie on topic Carburettor Query
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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4 years 2 weeks ago #885 by Batten
Replied by Batten on topic Carburettor Query
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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4 years 2 weeks ago #886 by keithsams
Replied by keithsams on topic Carburettor Query
i dont know what other bike used them anyone out there know ?
your bike is a late model so it may have had a casting fault and it has been machined out
at this point they were giving abcs away (wished i had been there)so not many questions were being asked

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3 years 9 months ago #963 by Batten
Replied by Batten on topic Carburettor Query
Dear All

Just to bring some closure to this topic, I now have a straight carb!

In further discussion with Keith he suggested that maybe the oddly angled carburettor mounting flange was another example of a factory mod. I guess a possible fault in the casting was cut/ground out allowing the carb to be used rather than scrapped. we will probably never know for sure.

Anyway attached are a couple of pictures of the fix.

Phil



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