Lotus Elan

Stromberg CDSE

PostPost by: Gorpon73 » Wed Sep 16, 2020 3:02 pm

Hello,

Question regarding the Stromberg CDSE which has fixed positions for the jet and needle. This is the model for which neither were adjustable.

I've found a wealth of info out there for the Strombergs in regards adjustment of the jet and/or needle, but not for the non-adjustable model. Two questions hoping to get some confirmation or help with in regards to the non-adjustable model.

- For the non-adjustable model are the starting positions the same as for the adjustable models? I've seen jet at 0.100" recessed and the needle shoulder square with the piston.

- For the non-adjustable carb, are these the presumed set-and-forget positions? Or is it recommended that the needle still be adjusted (by assembly and disassembly)?

Thx, DJS
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PostPost by: SENC » Wed Sep 16, 2020 3:14 pm

Google search this forum for stromberg and you'll find a recent thread post with some Lotus Service Bulletins on the topic - they recommended a .120" recess for the jet, as I recall.

It is the air valve/piston itself that defines whether the carb can have an adjustable needle - so you can swap pistons to use them if you wish. Otherwise, assuming jet height is correct, the fixed needle base (as I recall, I'm sure someone will correct if wrong) should be flush with the piston face. To get different results, rather than manually moving the needle you replace with a different profile needle - and there are some tables referenced in the various stromberg threads.
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PostPost by: Gorpon73 » Wed Sep 16, 2020 4:51 pm

Thanks. Looks like the 0.120" is where it needs to be. Should be good to get me going.

Finding a number of broken links for the needle profiles/applications. Any references greatly appreciated.

Cheers.
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PostPost by: SENC » Wed Sep 16, 2020 5:37 pm

I'll see if I saved links etc. this evening, but if you haven't found it Burlen maintains a Zenith Carb section on their website that is very useful in and of itself (looking through parts listing and drawings, etc.), and they offer a printed catalogue as well as a printed needle profile chart. Also google buckeye triumph and stromberg, there is useful article series there, too.
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PostPost by: david.g.chapman » Wed Sep 16, 2020 5:48 pm

I have "non-adjustable" needles in my +2. I vary the mixture setting by removing the piston and adjusting the needle in the piston by slackening the grub screw and re-positioning the needle to suit - up to richen the mixture and down to lean it out.

The effect is similar to the adjustable systems - you just have to keep removing the pistons every time. It does not take long to get the mixture you want - just start with the shoulder of the needle flush with the bottom of the piston and go from there....

Dave Chapman.
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PostPost by: Gorpon73 » Wed Sep 16, 2020 5:56 pm

Great. Thanks for the confirmation. Will have a go with it. Cheers.
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PostPost by: SENC » Thu Sep 17, 2020 2:15 am

A few useful threads and links:

viewtopic.php?f=40&t=43633&start=
viewtopic.php?f=40&t=25714&start=0
viewtopic.php?t=42511
viewtopic.php?f=40&t=21733

One of the posts on the 2nd page of the last thread has a stromberg needle profile spreadsheet.
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PostPost by: denicholls2 » Fri Sep 18, 2020 12:47 am

david.g.chapman wrote:The effect is similar to the adjustable systems - you just have to keep removing the pistons every time. It does not take long to get the mixture you want - just start with the shoulder of the needle flush with the bottom of the piston and go from there....


Yes, and the same is true for the SU. The adjustable method screws the jet up or down on the needle by 1/6 of a turn per flat, while relocating the needle accomplishes the same result but without the control of counting the flats. In my experience, the non-adjustable carbs all came too lean in case somebody actually checked the emissions and prevented setting a proper mixture.

The choke does the very same thing, mechanically moving the jet down relative to the needle to enrich the mixture, as opposed to most chokes which constrain the intake air instead (hence "choke") Really a better way to get there if all of the linkages are working properly because you can enrich the mixture on-demand without choking off the airflow (think high-altitude operation that requires a leaner mixture).
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PostPost by: SENC » Sun Sep 20, 2020 11:17 pm

Came across this while reading the DBE catalog this afternoon - may be useful.
Attachments
DBEneedles.jpg and
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PostPost by: Gorpon73 » Mon Sep 21, 2020 3:26 pm

Thanks for the updated info.

For information purposes, the links for the needle spreadsheet are broken on the GG Lotus webpage. But I did find the spreadsheet after searching around (attached).

Also, its worth noting for the next person searching on this topic....In terms of removal, everything I've ready says all the needle types can be removed (if they are stuck) by pressing them out the back of the piston. I found mine are mounted within the guide rod which is closed off behind the needle completely solid. It can only be removed by pulling the needle out from the bottom of the piston.

Thanks again for the info.
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stromberg_needles spreadsheet.xls
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PostPost by: 69S4 » Mon Sep 21, 2020 4:01 pm

So how's the car going? I must admit the existance of non adjustable Strombergs had got past me but I'd guess the 'slop' in the needle fit might allow a degree of adjustability. It's not as if you need to move the needle much from the datum point anyway - assuming everything else is ok with the carb.

The needle spreadsheet and the Dave Bean info sheet got me wondering what everyone else is using in their Strombergs. My UK spec S4SE came with BIY needles and I've stuck with them through thick and thin. I see on the DB sheet though that it's regarded as being on the rich side. It is what's mentioned in the workshop manual but that was 50+ yrs ago with a somewhat different petrol formulation. Should I be looking at an alternative and, if so, which? The other front runners seem to be the B1G and B2AR. Any feedback from anyone using those? Any others I should be considering?
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PostPost by: Gorpon73 » Mon Sep 21, 2020 6:43 pm

For my two cents:

- I found the spreadsheet somewhat interesting, but have only a basic understanding of it.
- The "Stromberg-Table" was also helpful in a sense that it confirms the few variables.
- Mine is a US spec S4SE. I went with the B1G's for a couple reasons. 1. It was what was there before, which worked reasonably well, even at altitude (I'm at nearly 4000 ft above sea level). 2. They seemed easiest to source new.
- There is a small amount of adjustment, even with the non-adjustables.
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