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stromberg CD150 carbs
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clascar



Joined: 27 Oct 2008
Posts: 83
Location: mid cheshire

PostPosted: Mon Oct 27, 2008 8:00 pm    Post subject: stromberg CD150 carbs Reply with quote

This is my first post and my query is the reason I found this site. I was on line looking for information on these carbs when I discovered this forum.
I have a Sunbeam with twin Zenith carbs. I have bought a pair of Strombergs as I believe they are a better carb. My engine is a 1592cc with an alloy head, I am told the Strombergs are off a similar engine but 1725cc in size.

My query is will these carbs need to be rejetted for my engine or will I be able to turn the mixture down. These carbs are the later ones with no external adjustment and with the plastic cover compensating valve cover.

I know this is a big ask for my first post.
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peter scott



Joined: 18 Dec 2007
Posts: 6212
Location: Edinburgh

PostPosted: Mon Oct 27, 2008 8:34 pm    Post subject: Reply with quote

Hi Clascar,

Welcome to the forum. I think needle profiles are probably determined empircally on a dynamometer. I don't really know about Strombergs but I suspect they will be specified rather like SUs which have their profiles specified by the diameter at either 13 or 16 points down the shank. I imagine that Rootes would start with a guess at a needle and then set the engine to a particular speed and load setting and then wind the jet up or down to find the best diameter for that carb slide opening and continue this process for all of the chosen number of slide openings.

I'm not sure anyone who hasn't tried the change could say what the effects might be. It's likely that other Alpine or Rapier owners have already tried this and you might get a better response from the appropriate one make club. Given that you already have the 1725 setup perhaps it would just be worth trying it and see if you get any flat spots or noticeably different fuel consumption.

Apologies for the rather unhelpful response,

Peter
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clascar



Joined: 27 Oct 2008
Posts: 83
Location: mid cheshire

PostPosted: Tue Oct 28, 2008 4:57 am    Post subject: Reply with quote

thanks Peter, unfortunately the Sunbeam Rapier Owners club site is not very active and I don't anticipate a reponse. From what I have found out on the web you are right about the needle settings and profiles being similar to SUs. I will clean them up, service them and give them a try. I have read an article on the Daimler site which offers instruction on how to balance the carbs off the car. I will try this as well and report back.
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peter scott



Joined: 18 Dec 2007
Posts: 6212
Location: Edinburgh

PostPosted: Tue Oct 28, 2008 11:32 am    Post subject: Reply with quote

Balancing the carbs shouldn't be a problem. You'll be able to set them up for a nice even tick-over but if the shape of the taper on the needles differs from what the 1592 engine requires then at higher revs and under load the mixture strength will be wrong and you will only be able to change this by swapping the needles for ones with more appropriate profile. Or, you'll adjust the jets to improve running at, say 2000 rpm, and it will no longer tick-over nicely.

Having said that, the two engines aren't that different and the 1725 needles might work perfectly well.

If you haven't already altered the jet settings on the Stombergs then I think it would be best to install them as is. Don't attempt to balance them off the car other than possibly the linkage between the two throttle spindles if that looks wrong.

Peter
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Jim Walker



Joined: 01 Oct 2008
Posts: 124
Location: Chesterfield, Derbys.

PostPosted: Tue Oct 28, 2008 5:46 pm    Post subject: Reply with quote

As you are talking about needles I presume you are talking about Stromberg CDs. Stromberg did also make fixed choke carbs.
Since you say there is no external adjustment, I believe the adjustment of your Stromberg Needles is by means of a long Allen Key inserted from the top down the damper tube. However, the diaphragm can be damaged/torn if the correct tool is not used. The Stromberg Tool is an Allen Key with a surrounding (pegged) tube which prevents rotational strain in the diaphragm.

Needle profile IS critical as already mentioned. As for jets - there is only the needle jet in the carb.

Presumably also, the Zeniths will be down draught carbs. while the Strombergs are side draught. Will the inlet manifold from the larger engine fit yours? It may be obvious, but don't try to fit the Strombergs other than as side draughts or gravity will mess everything up!

As for balancing off the car it may be the best way for a novice.
Set both float chamber floats exactly the same by inverting the carb. with float chamber removed so the float arm rests on the needle valve. The highest part of the float should normally be 18mm (but this can vary with type) above the float chamber flange. Cut an 18mm rectangle out of a spare bit of metal to make an 'L' shaped gauge.
Next, slacken the two screws securing the throttle butterfly and close the throttle firmly, making sure the tickover screw is backed off (both carbs). Tighten the screws. Use a piece of wire as a gauge to set both throttle valves open by the same amount with the tickover screw, then back off the tickover screws EQUALLY to firmly close the throttles, plus one more turn. Now adjust both needles to exactly the same position in the choke piston and re-assemble the carbs. As long as you connect up the throttle linkage in situ so that both throttle stop screws show an equal gap with feeler gauges your carbs are BALANCED but NOT TUNED.
As long as you move any adjustment equally on both carbs. you can play about to your heart's content to find the state of tune which is best.

Jim.
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clascar



Joined: 27 Oct 2008
Posts: 83
Location: mid cheshire

PostPosted: Tue Oct 28, 2008 10:00 pm    Post subject: Reply with quote

Thanks for the replies and useful advice. I have had a look at the carbs tonight in the dark, I think they are of the non adjustable main jet type. The information about balancing them off the car came from an expert who argues that the method I use with a suction gauge is not the most accurate. He says that setting them up carefully before fitting them is the way to go. I had never heard of this before. There is also a section which shows how to convert a non adjustable carb to adjustable and how to set the bi metal temperature compensator. The whole thing is 70 pages.

I think my best course of action is to strip clean and service the carbs. Then make sure they fit in their original orientation ie side draft. Then try them. There are sources for some parts but I cannot find someone with a range of needles.
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Rick
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Joined: 27 Apr 2005
Posts: 21130
Location: North-west UK

PostPosted: Tue Oct 28, 2008 10:18 pm    Post subject: Reply with quote

Not sure if its any use or not, I've a book here on Stromberg carbs and it has the following entry in it

Hillman Minx 1500-1725cc
Carb Ref F.6035
2x150CD
Metering Needle Code 7A
Air valve return spring Natural

The Sunbeam Alpine 1725cc (alloy head) and Sunbeam Rapier (alloy head) are both listed as having 2x150CD carbs, ref F.6039 metering needle code 14X. It doesn't list date periods though which would have helped, the book is from 1973 so may refer to later versions?

Rick
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clascar



Joined: 27 Oct 2008
Posts: 83
Location: mid cheshire

PostPosted: Tue Oct 28, 2008 11:14 pm    Post subject: Reply with quote

Good starting point Rick thanks
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Jim Walker



Joined: 01 Oct 2008
Posts: 124
Location: Chesterfield, Derbys.

PostPosted: Wed Oct 29, 2008 12:19 am    Post subject: Reply with quote

Experience does not cover everything, so I could have missed some later carbs, but ALL the CD 150s I have dealt with (which included Hillman Hunters) EITHER had an adjustable jet OR a needle adjusted via the damper tube. Surely a variable choke carb. MUST be adjustable to cope with throttle spindle wear etc? The bi-metal temperature sensor will not compensate for basic mal-adjustment of the throttle valves or mixture.

I agree with your expert that the suction gauge can be mis-leading, especially if the throttles are not balanced first.

Jim.
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clascar



Joined: 27 Oct 2008
Posts: 83
Location: mid cheshire

PostPosted: Wed Oct 29, 2008 11:06 pm    Post subject: Reply with quote

I don't know anything about these carbs Jim just what I have found on tinternet ie this site http://www.pclarkson.plus.com/downloads/Buckeye%20Stromberg2.pdf
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You should have done that, you should have done this. Ray
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peter scott



Joined: 18 Dec 2007
Posts: 6212
Location: Edinburgh

PostPosted: Thu Oct 30, 2008 12:05 am    Post subject: Reply with quote

Some links:

http://mk1-performance-conversions.co.uk/technical_carb.htm
http://www.sunbeamalpine.org/forum/archive/index.php?t-5687.html
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