Stromberg mixture needle question

[Yellelan]

I have a '69 S4 DHC with all history from new. It had new B2AR needles fitted sometime in the mid seventies, with another set fitted some years later, which are still fitted. It's also had a few new diaphrams fitted. The needles are about the right setting with the shoulder flush to the bottom of the air valve slider. It has many times been decoked throughout the years, far more than I would expect for the mileage (about 90k), and it's running very rich which I suspect is why it's coked-up periodically. Speaking to Zenith technical, they say needle B1Y was originally fitted to 69-71 Elans, and B2AR was fitted to 71-72 Elans.

So I suspect I may have the wrong needles, but what's puzzling is that my B2AR needles measures a larger diameter at the top and the bottom than the B1Y specification which means if I fitted B1Y's it would run even more rich for the same height setting.
Does anyone have experience/first hand knowledge or information on needles for the 69 Elan, along with expected frequency of requiring a decoke?

[SENC]

Where the jets are set relative to the "deck" is also important, as that defines the interaction between needle and jet (and thus the space for fuel flow). If those were replaced, it is possible they weren't set properly. The orifice in the jet also wears over time - if that is the case with yours, jet replacement may be more useful than needle replacement.

The following thread includes several Lotus Service Bulletins (last few posts) on the topic, and may be useful to you. Pure speculation, but these may have driven the swap to B2ARs.

I'm assuming yours is a non-federal, non-emmissions Lotus, since you have adjustable needles. Either that or it has been "upgraded". My recollection is that the B1Y is leaner at idle, richer at high throttle.

[Yellelan]

Thanks so much for your reply Henry. I suspect there's something not quite right about the jets as they do not look identically set in both carbs. I'm afraid a 'butcher' has been working on my carbs in years gone by, and the poor owner (whom I knew) was taken for a ride (with a very rich mixture!!)

[sng]

My Stromberg equipped car was running very rich after a long period of not being used. Adjusting the needle heights did not seem to make a big difference. I took the carbs off the car and set the float heights to the correct specification which were not correct and this seemed to help a lot. Sounds like you have some issues with needles etc. but worth making sure everything else is in spec as well.

[Yellelan]

I think you're right sng, the fact that some butcher in the past thought it'd be a good idea to replace those lovely spigot ended anti-rotation screws with a pointed lock screw (yes I do mean lock screw because that's what he wrote in his notes to the owner) and he actually tightened the point into the brass needle slider, damaging it so that it scraped grooves in the housing as I necessarily yanked it out with pliers due to it being jammed in by said numbskull, and also that there are no retaining clips (star washers) holding the adjusting screw in position.......all this means I can't trust anything about the carbs until I strip them right down and rebuild properly. I'm just feeling my way into the job, learning as I go as I've never stripped a carb before.
Thanks for your helpful comments!

[SENC]

Just noticed I mentioned a thread and didn't actually post a link. Here it is ir you haven't already found it.

viewtopic.php?t=41122

[Yellelan]

Just taken a closer look at the jets through the air valve hole, both are sitting about 3mm down from the 'deck'(?), meaning they'd have to be raised by that amount to make them flush.photos attached . Does this sound right to you?

[sng]

This is a photo of a jet from a spare carb I have. This carb is from a complete engine I bought a few decades ago, it has never run in my ownership but as far as I know it has not been 'reconditioned' since leaving the factory. The jets are sunk about 3 mmm but I am sure others can confirm. If not then let me know as I can take the tops of my running car and confirm.

Stromberg Jet photo

I am interested in how you get on with removing the grub screws, mine too are damaged, the brass is very soft and I guess reacts with the different metal in the pistons to seize.

[SENC]

See the LSBs in the link I posted. The jets should be recessed 0.12", or about 3mm, as pictured in @sng post. It may be an optical illusion, but in your picture it looks proud rather than recessed.

Remember that the needle is slightly offset and rubs on the inner wall of the jet orifice, which can wear. If the orifice looks oblong/worn rather than round, replacing them may be the best bet. Burlens has them.

If yours are seated correctly and look OK, I'd shift from looking at the carbs as the problem and reconsider ignition and timing. What distributor to you have, and has it been serviced?

[Yellelan]

It's an optical illusion, they are definitely recessed by about 3mm.
Have I got an adjustable jet? The fact there's a brass cylinder within a brass 'tubular' component (looking from the carb top) suggests it might be.
The photo attached shows a substantial brass plug which I haven't yet rotated which sticks out through the float chamber 'sump' , sealed in said sump via an O ring. If it ain't adjustable, then why bother exposing the end, necessitating a seal, and providing a screwdriver slot?

[Yellelan]

Aha, I just found a video showing the brass plug is just a blanking plug. Totally pointless to the design function, other than blocking the sump hole.

[Yellelan]

The plot thickens - I've found a stamp on the flange of each carb. I have two "S3296R" carbs. They also both have 920 stamped nearby. I've got the history of this vehicle from new, and there's only receipts for diaphragms, and needles, not replacement carbs.
Anybody got any clues as to what might be going on here, since I understood they should be 'F' and 'R'?

[SENC]

See below, but the F&R appear to have all the same components, so probably doesn't matter. Also note the B1Y needle you mentioned. The only reason I can think of that they'd be differentiated is that at some point (if memory serves), the Elans only included the choke mechanism on one carb, with the other plated off. My 3296 carbs are at my shop, I'll have to check if I actually have an F&R or two Rs... but as I recall mine had choke mechanisms on both.

It could also be as simple as Lotus using what they had or not playing close attention to F&R, particularly if interchangeable.

[Yellelan]

Mine has a choke mechanism on both, but only the front (radiator end) operates from the cable. It had crossed my mind that it might be Lotus using what they had (the two R's).
I can't read the thing you posted but is it saying the 69 Elan with those carbs were fitted with B1Y needles? This might make sense as it would run a bit leaner for the same needle height and jet size. There's no record of changing the jet on my car, only the needles and it wouldn't surprise me to find the wrong needle was fitted.
Thanks for your help.

[SENC]

Click on the image to "open" it and it should be clearer... but, yes, 3296 came with B1Y according to that Burlens manual.