Lotus Elan

stromberg jet height, what is yours?

PostPost by: saildrive2001 » Thu Jan 20, 2011 9:20 pm

The tools look good & I am sure as you have found out would work. My concern would be the load on the threaded parts of the carbs when using the tools. When I removed the jets form my almost 40 year old carbs I needed a fair amount of force using a press. I also found it ideal to heat the carb body & chill the new jet in the freezer before pressing in the new jets.
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PostPost by: davea » Thu Jan 27, 2011 12:23 am

Been cold and rainy (by California standards) and busy so nothing done.
But now warm and time-sensitive task completed, so perhaps tomorrow
I'll get in some data logging. I was astonished and discouraged that
raising the jets 0.030in only leaned the AF ratio by 1 or 2 points to 11/1 or so at idle
and this with new B1Y needles. Way rich. Is the fuel float level too high (in spite
of it seeming right as measured)? Need to take a full logging run now it's nice out. More later.
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PostPost by: davea » Thu Jan 27, 2011 10:42 pm

With B1Y needles and jets at 0.092 inches below the bridge and fuel floats
at 16mm. It is leaner than before, but not much.

Idle 11/1
45mph cruise 12-14.1
70mph cruise 13-14.6/1
WOT up a hill, in 2nd to 6000: 12.5/1
Continuing in 4th WOT to 70 mph: 13.6/1

Not the pattern one really wants, but not obviously dangerous to the engine.
Accidentally skipped 3rd gear (oops) in
the acceleration.

I really think I need an rpm position sensor to understand the log better -
at least I hope that would help my understanding when the mixture wavers all
over like it does.
The log is 2011-1-27-b1y-jetat092-2chan.log on reality.sgiweb.org/davea/elan.html

I wonder what lowering the fuel level in the float bowl by 1-2mm would do. And I wonder
if Grose-jets as the float-valve would make a difference.
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PostPost by: m750rider » Sat Jan 29, 2011 2:28 pm

can you lower the needles any?
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PostPost by: davea » Sat Jan 29, 2011 5:23 pm

The needles (more precisely --- the needle holders) are at the bottom of the pistons.
There is only a 1/4 turn of adjustment of the needle holder left
before the needle falls off the threads, so it attempting to
push the needle down further is not workable. Of course the needle/holder won't fall out
because of the little spring-loaded screw in the side of the piston extending
into the slot in the needle-holder, but you will
lose control of the location of the needle...
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PostPost by: 69S4 » Sun Jan 30, 2011 10:17 am

I've been following your posts with interest as fine tuning Elan Strombergs using actual data rather than just seat of the pants or information that dates from the "classic era" isn't something I've seen much of and despite a complete rebuild of the carbs on my S4 last spring I'm still not completely happy with the way they're working.

You're probably aware of the Triumph TR6 site that covers the same ground for that car. If not, here's a link - http://www.buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm. He also built an air/fuel monitor to look at what was happening inside the carbs and on the face of it his numbers don't seem that different to yours.

I'm still a bit confused over the interrelationship between a number of the adjustments that are possible with Strombergs. With a "normal" slide carb - the sort found on many motorcycles - you can adjust a number of items to fine tune the response eg main jet size, needle position, slide cutaway etc. With Strombergs virtually all of those adjustments are built into the needle profile. You set the needle to a datum point (level with the bottom of the piston) and if the jet is in the correct position, you should get the response the profile was designed to give. You can fine tune it (+/- 1/2 turn) to allow for individual variance but if it's miles out you need another needle that gives the characteristics you want. Looking at what you've posted, you're running rich and to correct that you've lowered the needle to the limit of its adjustment. It's better but it's still rich. The other half of the combination, the jet, is set .090" below the top of the body, a figure that from the information the rest of us have would seem to be about right but I've not come across any definitive figure for that. If you pushed it up another 0.010" you would have some more adjustment but the jet height would be outside of what's thought to be the normal height range.

Sadly at the end of all that I've no answers, only more questions.

You have a huge advantage in getting information from the data logger but how much of that corresponds with how the car feels? (touchy, feeley tuning - it is a hippy era car :lol: )
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PostPost by: davea » Tue Feb 01, 2011 9:06 pm

Thanks for the link to the Triumph site, I was not aware of it.

Today did back to back test runs, first with b1Y then with
B2AR. The idle (in the logs) is too fast once things
warm up.

The raw logs are available from reality.sgiweb.org/davea/elan.html
(look near the bottom of that page).

In the first two tests the needles were adjusted to just even
with the bottom of the piston (which is almost exactly
2.5 turns from fully up). In Dyno runs a few years ago
with B2AR (but before the carb rebuild) we discovered
that needle location was a bit too lean at WOT for
max power. Which is
data that is supported by the B2AR WOT runs.
Of course adjusting for WOT is going to mean much too rich
at idle and on the highway....

B1Y, needle level with piston (session 2 in the log)
idle 11.5/1
Freeway cruise 14.5/1
WOT 3rd and 4th gear 13.2/1
45mph local cruise 2000rpm 13/1


B2AR, needle level with piston
idle 1500 rpm 11.3/1
Freeway cruise 14.5/1
WOT 3rd and 4th gear 12.5 - 14/1
45mph local cruise 2000rpm 12-14:w


B2AR 1/2 turn of needle -- richer
idle 10.8/1
Freeway cruise 13.5/1
WOT 3rd and 4th gear 12.5 - 14/1
45mph local cruise 2000rpm 11.5-13.5/1
This is pointlessly rich in cruise, but is better
for track use/repeated WOT.

The B2ARs behave oddly at WOT. The mixture strength declines
as the revs go up(to 6000 in 3rd, and again in 4th to 4500rpm).
Whereas the B1Ys retain a constant-ish mixture strength.

The acceleration felt better with the B2ARs, I do not know
if that was the car or the driver, but it felt like there
was a bit more acceleration, the engine was a bit more responsive.

There are some rpm bobbles
in the acceleration, the freeway ramp is upward and easy
but has semi-filled potholes about half way up which cause some
excitement (wheel bounce). Though a bit of swerving about
avoids the potholes.

The log files are fairly simple text files but
not something one can work with in a spreadsheet
without some massaging, and I have not yet written code
to massage the data into spreadsheet-friendly form.
Basically there are 3 data tracks with data: Time in seconds,
AF ratio, and rpm.

All in all, for now I will turn the B2ARs back down to level
with the piston bottom and run with that a while, I think.
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PostPost by: 106500 » Sat Dec 21, 2013 7:23 pm

I have just fitted adjustable jets to the CD2 Strombergs on my S4. I have also replaced the needles. I am experiencing some difficulty setting these up. The jet surfaces are adjusted well below the 'bridge' (to the point that the left hand adjuster is touching the pedal box) and the needle shoulders are adjusted well below the surface of the carrier yet the mixture still appears lean and the car is hesitating when driven. Not sure why this might be the case? Thoughts welcome please.
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PostPost by: 106500 » Sun Dec 22, 2013 12:03 pm

I've switched from B1Y to B2AR needles - would this make a difference - does one run richer than the other?
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PostPost by: oldelanman » Sun Dec 22, 2013 12:23 pm

106500 wrote:I've switched from B1Y to B2AR needles - would this make a difference - does one run richer than the other?


This spreadsheet allows you to compare needles, the B2AR looks richer at idle and top end and leaner in the mid-range than the BIY
Attachments
stromberg_needles spreadsheet.xls
(60.5 KiB) Downloaded 842 times
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PostPost by: 106500 » Sun Dec 22, 2013 1:50 pm

Thanks. What I don't understand is that I have the jet adjusters screwed down so low the bottom of the left carb is hitting the pedal box yet the mixture is still lean (I have also screwed the needles up as far as they'll go as well)! - there are no air leaks either....
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PostPost by: oldelanman » Sun Dec 22, 2013 2:22 pm

I have no experience with adjustable jets but I would think the basic relationship between needle and jet must be the same as with a fixed jet and adjustable needle. If that is so ....and I stress I do not know that for sure... then a good starting point would be with the shoulder of the needle flush with the base of the air valve (piston) and the jet set 2.4mm below the bridge. A small adjustment of the jet should be all that is required from there to get the mixture right, if that doesn't work and large adjustments make no difference it points to a problem somewhere.
I am sure you have done so already but the usual things to check for are air leaks, float levels, sticking air valves, torn or deformed diaphragms, incorrect or missing dashpot damper oil. Also check that the choke levers are returning fully to the off position.

Edit: Sorry. Forget the last check.....I see you are running too lean not too rich !
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PostPost by: 106500 » Tue Dec 24, 2013 5:17 pm

All carburation issues sorted. Had to drill hole in pedal box to accommodate adjusters. Running nicely now. help and advice was appreciated.
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PostPost by: h20hamelan » Wed Sep 15, 2021 2:56 am

https://web.archive.org/web/20110913165 ... /elan.html

Nice the wayback machine is still working
Still cant figure out what’s up with mine
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