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MG Midget and Sprite Technical - midget 1500 mixture lean on accel

Hi everyone,

Hope you're all well.

I have a problem with the transient fueling on the midget.

Everything is spot on, valve clearances, plugs, points, plug leads, compressions, float heights, jet heights, etc etc.

Its a 1974 Midget 1500 with a high flow air filter and a 4-2-1 tubular exhaust with 2 straight through silencers.
The needles are AAQs and are both set at the same height.
I have 20/50 oil in the dashpots and STD springs.

I have my lambda sensor as far forward as is humanly possible (in the 2-1 collector) and the AFR gauge in an easy to see location on the dash.

I know the lambda and gauge are good as it was bloody expensive and I used it on my ww2 jeep and motorbike and they run spot on.

So..
Cruising mixture is dead on but its lean on acceleration and misses a bit.

Any suggestions ?
Raise needles a bit ?
Different springs ?

Would be good to hear peoples thoughts.

Cheers.
Skelly.






Jon Skelly

What colour springs are you using?

For the cost of a little oil wastage you could try straight 20 weight SAE oil instead of 20w50. Easy and cheap to try (if you already have the 20 SAE or someone can give you the small amount required).

3-in-1 white tin is 17 SAE but the 3-in-1 blue tin motor oil is/used to be 20 SAE or purpose sold SU/Zenith or Penrite 20 SAE Damper oil.

20 SAE is of course within a range, as are 20w50 which can be at different places in the ranges to another 20w50 so there can be small differences.

The viscosity chart, of course.




Nigel Atkins

Jon
It shouldn't be lean enough to missfire with them needles
Don't get tricked by your AFR gauge, If you have an electrical missfire caused by faulty plugs/leads,etc, then that missfire will show on the gauge as lean when it missfires
Try getting a bit of load on at the same revs,working around the missfire area and check your mixture there, then make it missfire and see if that is what is making it show up lean

willy
William Revit

A wide band lambda is such a useful tool. I ran one with my DCOE for years and still do with my new EFI system. But it can get a bit distracting and throw a few curve balls...

Ignoring what the lambda says. Are you SURE it is a misfire due to a lean condition?

The lambda is working on the assumption you are achieving "proper" combustion and sensing the remaining O2 in the exhaust gasses. If you have a misfire from an overly rich mixture or other ignition issue, the oxygen is not used completly and properly in the combustion and sent out of the exhaust. The lambda then incorrectly senses this as a lean condition as it is only sensing the oxygen, not unburnt hydrocarbons!

Does that make sense?

Malc.

Edit: really smart looking car by the way :-)
Malcolm Le Chevalier

Sorry, I missed (no pun intended) the very last bit of the post which had " misses a bit".

Rule of thumb, carb ignition problems are more often electric ignition problems. Check your dissy cap and rotor as well as double your plugs and leads and treble check anything to do with points.

Always worth checking for indirect if not direct all electrical wires and connection and switch are all fully functioning and clean, secure and protected.

Earth wires and other wires and connections related to those nasty CB points often come up as curprils for intermittent or problem only at a certain point (to start with at least).

If you've fitted new ignition parts especially CB points, condenser - but I think we went through this before.

I had a problem and decided to follow my own advice for once and start the service checks, tappets etc., sure enough it was the dissy cap which I know was fine not 6 months ago when I last checked.
Nigel Atkins

Jon
,Sorry I've given you a bum steer, AAQ are way too lean (That's a lesson for me -thinking I knew and not looking them up) --you need to try some AAM needles
sorry about that-
willy

AAM
William Revit

I have just been through something similar, 1500, K&N filters, Maniflow LCB manifold, and needed to change from the standard needles to AAM.

On acceleration and towards the upper rev range the mixture was too lean causing a bogged down or hesitation sensation.

Funnily enough it was Willy who confirmed that I needed AAM !!!

Chris Madge

As soon as I saw Willy's correction I thought of Chris's thread and then luckily saw Chris's post before I went unnecessarily looking for the thread.

Willy how could you do it, confuse me more than I already am, I don't know if I should congratulate you or scald you, see you still have me confused, this could go on for quite a while.
Nigel Atkins

Nigel- I'd really really like to be congratulated by you for owning up to my blunderous error, I hate it when i do that , so if you could possibly make me feel better by sending chocolate or beer, then so be it

willy

Jon
AAM needles and stay with the std. springs.
William Revit

Nice idea Willy, it made me wonder if anyone made chocolate beer and of course they do https://www.thespruceeats.com/best-chocolate-beer-353056 , I like both in moderation but I just don't like the idea of chocolate beer. Maybe like green eggs and ham if I tried it I might change my mind.
David Billington

Chocolate beer --Hmmmm - No, I don't think I could-
I enjoy a nice bitter ale and I like chocolate, but both in the same glass, I'm not so sure
William Revit

Willy,
I congratulate you on spotting your mistake and correcting it, I'd gladly give you some chocolate if you were nearer.

The heat of the weather here is making me even more confused than usual, if that's possible.

I never even attempt to remember needle letters and of course if the car's not standard there'd be even more variations to remember.
Nigel Atkins

I like chocolate but not chocolate flavours, and I like ale (rather than beer as I'm a "beer snob/bore") but the last year or so I started drinking (real ale) stouts, some with chocolate flavour or chocolate and something else and some were very nice, can't think of the names now though.

Bottled beer (which is not real ale) may give an idea, or even good idea, of the taste and quality but it's second (or third)) league compared to a well kept and served real ale out of a barrel (not keg).

Bottled beer is like a supermarket made "indian" curry compared to a Bangladeshi "indian" take-away shop curry, they're both curries but a league or two apart.

Nigel Atkins

Had some New England Almond milk coffee stout the other day, it was ok and just a tiddle chocolatey but still not over convinced it should be in one glass though
William Revit

Willy,
that looks a good beer and a good brewery.

Not my cup of tea, so to speak, as it's as they say a carbonated beer but it looks I'm sure as it'd be thre or four leagues up on the mass produced canned and bottled beers and lagers.

It'd be a youngsters beer over here, highly thought of by it's consumers - and highly priced, UK snob values dictate you pay for and advertise the logo/label/brand and the fact that you yourself are able to buy overpriced items.

That's not to take away from the fact that many of these brewers make very good products (fizzy, keg though).

This video with the New England Brewing Co. shows the passion that is in the product - https://www.youtube.com/watch?v=3tLlbgh8800
Nigel Atkins

This thread was discussed between 22/06/2020 and 26/06/2020

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