Stromberg jet height

Talk about the E-Type Series 3

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nigeld
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#1 Stromberg jet height

Post by nigeld » Tue Aug 04, 2020 7:29 pm

Im trying to get my 1973 UK spec car to run better.

I'm rebuilding the Strombergs. Is there a definitive figure for how far below the bridge to set the jets? The rebuild instructions from Burlen say "as you found them" but mine look different to each other (have not used the vernier yet). I have found 2.5mm mentioned by the experts on this forum. But Is that to the inner face or outer ring of the jet? (the outer ring being slightly raised).

When the car was running it seemed to be running very rich (black acrid exhaust). I have seen mention of adjusting the mixture but (in contrast to SUs I'm used to) there is no mixture adjustment on the standard Strombergs. Is mixture adjustment done by moving the needles? How do i do that? Cant find any instructions for that.

Thanks

Nigel

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rossco_j
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#2 Re: Stromberg jet height

Post by rossco_j » Tue Aug 04, 2020 10:16 pm

pm sent
Ross
1972 Series 3 E Type 2+2
1972 MGB GT
1965 Mini Cooper
https://rossjohnsonphotography.zenfolio.com/

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vee12eman
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#3 Re: Stromberg jet height

Post by vee12eman » Wed Aug 05, 2020 3:40 am

Hi,
It’s a question I’d like the answer to as well. I think it’s 100 thou (0.1”), but I don’t think mine were set to that depth. Unfortunately this was years ago when I didn’t have the facilities to measure accurately and I made a rough and ready jig to do it. The measurements are taken to the top of the shoulder of the jet (the outer ring as you put it).

Can anyone confirm the above?

Adjusting the needle is through the dash pot lid with a special tool, a long Allen Key with a top hat section insert. The insert has a pin which engages in the slot at the top of the piston, to stop it rotating when you adjust, which runs the risk of tearing the diaphragm. The Allen Key goes through and into a nut at the bottom of the dash pot reservoir and rotating it causes the needle to rise (strengthening the mixture) or lower ( weakening it). These nuts have seals around them to keep the damper fluid contained, but most are now leaking so should be replaced. It’s often overlooked or even deliberately ignored as replacement automatically requires tuning.

You have to remove the grub screw from the piston. When refitted, this engages in a slot at the top of the needle and should allow limited up/down movement under the influence of the adjustments using the aforementioned nut. Remove the needle and the brass cylindrical base, they often stick so you have to free them sometimes, gently of course. The nut and retaining clip can be seen below, you have to gently tap them out with a long punch, don’t lose the retaining clip (looks like a spring washer). Seals available from Burlen Fuel Systems amongst others and often come complete with new nuts. Seals are around the outside of the nut.


Image

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Image

Regards,

Simon
Last edited by vee12eman on Wed Aug 05, 2020 8:25 pm, edited 1 time in total.
Simon S-Y
Series III FHC

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Bob.
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#4 Re: Stromberg jet height

Post by Bob. » Wed Aug 05, 2020 1:05 pm

Jet outer land 2.5±0.3mm below the bridge face (orifice is 0.5mm lower). Data was verbal from Burlen Fuel Systems Ltd in Jan 2017 after they had consulted their drawings. It worked for me with factory settings of 16.5±0.5mm for float levels and 1.5psi fuel pressure. (sorry for mixing units)
See also topic viewtopic.php?f=6&t=16075&p=131987#p131987.
Bob
'71 S3

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nigeld
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#5 Re: Stromberg jet height

Post by nigeld » Wed Aug 05, 2020 1:37 pm

thanks all. I will set them at 2.5mm below the bridge to the outer ring. Interesting to see that I am yet another Nigel with a Series 3 ...

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71 V12
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#6 Re: Stromberg jet height

Post by 71 V12 » Fri Aug 07, 2020 9:43 am

Related to this topic, can anyone confirm a source for the spring clip circled in Simons photo. I want to be able to replace the rubber o rings on the adjuster without having to buy kits from Burlen.

Apologies Simon for using your photo, I hope OK.
Image

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#7 Re: Stromberg jet height

Post by Bob. » Fri Aug 07, 2020 12:13 pm

I found Burlen quite happy to provide individual items, give them a ring.
Bob
'71 S3

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vee12eman
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#8 Re: Stromberg jet height

Post by vee12eman » Fri Aug 07, 2020 1:14 pm

No worries in using the photo, they were added to help. I re-used the spring clips with no issues so unless you have lost or damaged them, you should be fine. If they are loose, then very carefully tap them a little flatter with a light tap from a hammer before re-using. Burlen should be fine to supply individual items.

Regards,

Simon
Simon S-Y
Series III FHC

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71 V12
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#9 Re: Stromberg jet height

Post by 71 V12 » Fri Aug 07, 2020 4:42 pm

Thanks Simon, good to know you can reuse them👍👍

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Doddsy
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#10 Re: Stromberg jet height

Post by Doddsy » Sat Aug 08, 2020 8:38 pm

Nigel ( I'm yet another Series 3 Nigel owner), I have been having problems setting the idle on my car, hence all my posts. I eventually measured the depth of the jets (which I had replaced when rebuilding my car). Mine are set a bit too high at .070 inch 1.5mm below the bridge as measured to the outer land of the jet (not to the jet itself). My car is running fine but i am on the limit of the adjusting screw (fully clockwise) and I would like to enrich further just to see what the difference would be. I recall reading on another post that the adjustment screw can add .030 inch so this sort of fits with the correct depth being 2.5mm .100 inch as you suggest.

I was looking for a way to press these to the 2.5mm .100 inch insitu. I dont like the idea of resorting to a punch (suitably limited) and hammer again (this was how I set them originally). I am now resigned to leaving this until next winter and enjoying my car this summer. FWIW.
Teddington UK. Series 3 OTS 1972. Owned since 1982.

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Tbob
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#11 Re: Stromberg jet height

Post by Tbob » Sat Aug 08, 2020 8:50 pm

71 V12 wrote:
Fri Aug 07, 2020 9:43 am
Related to this topic, can anyone confirm a source for the spring clip circled in Simons photo. I want to be able to replace the rubber o rings on the adjuster without having to buy kits from Burlen.

Apologies Simon for using your photo, I hope OK.
Image
Joe Curto sells these and the o rings as a kit.
Bob t

LHD '69 OTS. (Former) basket case

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#12 Re: Stromberg jet height

Post by Norton » Sat Oct 03, 2020 9:32 am

Have been reading with interest. Adjustng mixture with the allen key adjusting tool, is it correct that clockvise will weaken mixture and anti clockwise will richen? ( as seen from above )
All RH plugs are sooty but dry. Will it be a good idea to try weaken mixture on RH carburettors by lowering needle?
Harald
Last edited by Norton on Sat Oct 03, 2020 10:30 am, edited 1 time in total.

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vee12eman
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#13 Re: Stromberg jet height

Post by vee12eman » Sat Oct 03, 2020 10:16 am

Hi Harald,

Clockwise means the needle rises, the nut stays still but the needle is drawn upwards as the nut (effectively) tries to screw itself down the needle carrier. As the needle is tapered, this enriches the mixture, whereas anti clockwise pushes the needle down and weakens the mixture. Hope that’s clear.

Simon
Simon S-Y
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Norton
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#14 Re: Stromberg jet height

Post by Norton » Sat Oct 03, 2020 10:32 am

Thank you, very clear. I had it apart last year to replace O ring but could not remember which part was fixed or not.
All RH plugs are sooty but dry. Will it be a good idea to try weaken mixture on RH carburettors by lowering needle?

Harald

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#15 Re: Stromberg jet height

Post by vee12eman » Sat Oct 03, 2020 1:03 pm

Hi Harald,

You can try, but best to have some way of checking the mixture. I use a Colortune kit or, if feeling lazy, I lift the piston a very small amount, I use a scriber with a taper, push it into the inlet and it causes the piston to rise very slightly, only a mm or so. From memory, if the engine revs rise mixture is too rich, if it falls, too weak whereas if it stays more or less constant speeds, it’s ok. Difficult to get right, it is only a very small lift or the revs will drop anyway and it’s hard to detect on the V12 as one carb has minimal effect.

Using a scriber or long slim flat blade screwdriver makes the results consistent - pushing it in gently Forces the piston up a small and consistent amount. It’s difficult to describe but does work with care.

Regards,

Simon
Simon S-Y
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Norton
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#16 Re: Stromberg jet height

Post by Norton » Sat Oct 03, 2020 7:17 pm

Hi Simon.
Thanks again, I’ll give it a try.
I lowered the needles as much as was possible. About .5mm. But no significant change on spark plug appearence. Still sooty black. I still think the mixture is too rich, how can I make it leaner? I am neww to Strombergs..
Rgds Harald

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#17 Re: Stromberg jet height

Post by vee12eman » Sat Oct 03, 2020 11:22 pm

Hi again

Unleaded petrol sometimes does look rich at the plug, at least in my experience. I find it less helpful than in the days of leaded fuel, although I know others feel that it’s still useful to look at the colour. I think you’re supposed to look right down at the insulator of the plug. Also did you drive the car long enough to clear the old deposits? I still recommend a form of testing while actually adjusting, as in my previous post.

Other sources of rich mixture might include the choke not being fully closed on one or both banks. Check that the fast idle screw is clear on both sides. Choke assemblies can leak or be worn too. If the floats are at the wrong height this can have an effect, but you have to remove the carbs and check that, then you need a seal kit and then you are into a refresh/rebuild process if you feel confident enough.

Good luck with it,

Simon
Simon S-Y
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Norton
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#18 Re: Stromberg jet height

Post by Norton » Sun Oct 04, 2020 1:31 pm

Hi and thanks for advice. Forgot to mention that I fitted new plugs after adjusting needles. And as the old plugs, looking healthy on left cylinder bank and sooty on right side after a short test run ( 20 miles ). Fast idle screws are clear, chokes fully closed at least looks closed from outside of carburettors... Leaks, wear and tear might be a factor but then need to dig deeper.
Harald.

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#19 Re: Stromberg jet height

Post by SESH » Mon Oct 05, 2020 11:51 am

Had my V12 professionally tuned on a rolling road, most of my running problems came from vacuum leaks. Plus I also had a Stromberg carb needle modification done (X4).
Mike
1973 Series 3 OTS Signal Red

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driver
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#20 Re: Stromberg jet height

Post by driver » Mon Oct 05, 2020 8:24 pm

Hi, just reading the previous post,
how were your needles adjusted.
Thanks Rob Gill
v12 etype 2+2

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