Checking Mk1 Stag carb jets/needles, 4 speed auto

[Triumphman]

Evening All. On my MOT test earlier this year, the emissions were 4.5%, it passed anyway as emissions was tested after the certificate, as I had asked for a check. Fuel consumption is always low 20's even with a very light right boot. I've owned the stag for 4 years, done about 5000 miles & it runs well, idles @ 600, no missing, plugs look good, tappets/timing all good. After the emissions test I thought I'd weaken the mixture by 1/4 turn on each, 1 side was fully down, other side was 1/4 from fully down. Carbs o/hauled by well known company 3 yrs ago. (Before fitting carbs I checked float levels & needle positions, all ok, setting them up with colortune & carb balancer). Thought I'd remove carbs to check things, needles removed to check numbers - B1AQ on 1 & B20261 on the other, which according to Burlen is ok as 20261 is part No for B1AQ & not worn, needles were sitting up in slides by 0.063, shoulder of jet is recessed by about the same.
I've read that the jet should be about 0.100" down, is it that critical? Also that the needle washer should be level with the slide as a starting point & that should more or less run well?
Also, why did the needle that was fully down not drop out of the adjuster?
Sorry for the long post, I've tried to include all the info!
Cheers
Paul

[richardthestag]

Hi Triumphman

4.5% is achievable on even a set of worn Strombergs. However sometimes getting it to run leaner is not always the answer.

Jet depth is important. measurement is tricky because of the ridge around the jet and width of the piston hole.

If the jet is set too low or too high then the mixture will never be right. Remove a piston and meter needle and see how much adjustment you have with the tool running through the top... it isn't a lot

I got my stromberg carbs to run at 2.5%CO fairly easily. I use a CO probe up the exhaust, it is happier at 3.5% but then have gotten used to supermarket fuels. Not used my stag in a couple of years for a number of reasons....

The start point for tuning which I bang on about all the time in my youtube videos is only to aid the tune process.

For example if;
Both jets are new and recessed to the same depth
Both needles are the same
Both needle are engaged to the adjuster and set to me level with the edge of the piston
Both float levels are set the same
Both temp compensators are set to be closed at ambient
Both idle screws are engaged with the stop and wound .5 turn

Then the engine will start. If it starts let it warm and you can tune.

[richardthestag]

This is the latest stag vid that I did

https://youtu.be/JkD8I5IbItY

More recently I had a very expensive stag in that had a sticky LH choke module and bone china fuel lines.

Both left running beautifully

[Triumphman]

great videos Richard.

[Triumphman]

Ok, what I've found is, the needle valve jet adjusters are at different heights from the bottom of the slide, which means they engage with the needle at different lengths, 1 @ 0.567, the other 0.610, this is why 1 of the needles didn't disengage from the adjuster until the grub screw had been removed. Is there a shoulder inside the slide to locate the adjuster?
Cheers
Paul

[trunt]

Yes, the adjuster sits on a ridge in the bore.. Inside the piston bore the adjusting screw is retained by a star washer, if the star washer slips up, the adjuster will be further away from the needle, Try putting a rod or something just smaller than the piston bore down it and tap it down to seat the spring washer and screw right at the bottom. If there's still a difference then maybe push the adjuster and washer out upwards and check for something at the bottom, maybe an old O ring? Good time to replace those O rings!

[Triumphman]

Thanks trunt, but, if the adj was not far enough down, would the adj move .IE between the ridge & the star washer.
BTW, my o rings don't leak, yet!
Just read your message again! Of course if there's an old o ring in there, that would stop it moving & I guess that would measure 0.040 odd, more investigative work tomorrow then
Cheers
Paul

[richardthestag]

If the adjuster was not far enough down inside the piston then it would not reach the meter needle. The star washer is essential to hold the adjuster in place

Happy Christmas

[Triumphman]

Thanks Richard, I realise that. I've now pushed the adj's out & had a good measure of things. after refitting needle & adj w/out o ring, 1 needle is approx 0.040" longer measured from the bottom of the slide. I have found out why, one needle/adj is 0.016" longer than the other & the slide is longer than the other by 0.025, at least I've found where the difference lies.
As for a solution, easiest way is to mill a longer slot in the needle.
I'll update when I get it done, next year now!
Beery Christmas & a New Year with good health to all
Paul

[trunt]

Not sure if the needle is supposed to disengage from the adjuster without removing the locating screw? if it did then you could not pick it up again should you go too far lean..

Can’t you just swap needles/adjusters around to minimise the difference?

[richardthestag]

Sounds like the needles have come from 2 different places, order another from Burlen and make up a matching set would be my suggestion.

The position of the adjuster will allow the need to disengage at the weakest setting, i.e. needle right out as far as it will go. The depth of the slot and the grub screw "should" allow the needle to just be in grabbing distance of the adjuster to wind it back in again.

I always check that I can wind the needle fully in both directions and that the thread does reconnect instantly before setting them at the baseline. Stuff from Burlen never misbehaves.

Beery Christmas to you also

[Triumphman]

Trunt, yes should be able to do that, I would rather keep needle & jet matched together tho'
richard, i think I'll check before getting the needle, I know they're not expensive, as stag things go, just want to make sure it's the right decision.
Cheers All
Paul