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MG Midget and Sprite Technical - suneedle program

The Suneedle program is very helpful. I use a V3 needle now.(HS2, 1300cc) It is all right at High RPM > 3500 RPM but too rich at low RPM <3000RPM. Nice at Idle and pick up. How do I find the right needle with Suneedle? There is too much choice.

Flip

www.mintilamb.co.uk/suneedle
Flip Br�hl

A knowledgeable and trustworthy rolling road tune (tuner) would be best otherwise you might be getting a selection of approximation based on how things are set now up now.

Unless you have reliable run date from your car whilst it's actually being driven on the road from some clever electronics.


Nigel Atkins

Nigel,

You are right. I ll go to Peter Burgess but he is not next door. I dislike to use a trailer. To come there I ll have to find a needle that is a little bit rich to be safe.
I use several methods:
-Listening in al RPM (and my nose at idle)
-Acceleration
-Looking at the spark plug
-MPG

-I used to listen to two stroke engines to set the mixture, as a 13 year old, a Webra 2.5 diesel in an airplane, later mopeds, motors, nowadays 55 years later Stihl chainsaws. My hearing is less than when I was 13.... but I can roughly judge and set the mixture by listening.
The 123 has the right software to measure acceleration. I can not set the ignition by listening.
The spark plug looks right after driving >65 MPH, dark after slow driving.
< 60 MPH
- 44 MPH at 130 KM/H, 38MPH at 90 KM/H!!!!!

I am aware the the ignition is not spot on in the low range.
Above are the reasons I am looking for a leaner needle in the low RPM.

Flip
Flip Br�hl

My post was a general one which I hoped would encourage others with much more detail for you.

Not that I know anything about it, I think you've done as much as you can and need the help of another that can read and understand these needle profile charts more.

I expect you already do this anyway but acceleration comparisons would need to be with very consistent circumstances and environments.

I'm not a big fan of looking at spark plugs for other than very wide general condition, surely you'd have to immediately shut the engine off and check the plugs at various points of a run rather than one end reading.

MPG I think is a reasonable overall measure but again relies on very accurate measurements and very consistent circumstances and environments.

I follow -
"The spark plug looks right after driving >65 MPH,"

and do you mean(?) "dark after slow driving < 60 MPH.".

But I'm lost with - "- 44 MPH at 130 KM/H, 38MPH at 90 KM/H!!!!!".

You probably got them but don't you need an SU needle identification chart (which I can't find) or SU needle calculator such as -
http://www.teglerizer.com/suneedledb/

and something like SU comparison chart- http://sucarb.co.uk/needle-comparison

PDF is for HS2.


View PDF:
Nigel Atkins

You could try a pair of "M" needles
They are std 1275 mini needles and just a tiddle leaner than V3 in that lower rev range
They should be safe in your 1300 as it will run a little richer than the 1275 being larger capacity anyway
William Revit

Flip

If I send you a recording will you tell me what I need to do to reset my Stihl?

It wasn't revving as freely as it should last time out.

Colin

PS. No, I'm not being serious! :)
C Mee

It is not just a question of the needle, the springs play an important part and the pistons should only just reach full travel at full throttle. If they reach full travel before full throttle then it effectively leans out the top end.

I would go with Willy's suggestion of a pair of M needles to start with and get it to Peter when you can.
Chris at Octarine Services

I 'll order the M. As I can clearly feel the difference between V2 and V3. I suspect it to be better (I have 8 pairs of needles. I started with the 6, than GC, V2, and ended with V3 as I do not dare to use AN, and Leaner;GX, EB and MOW)
I use the soft dark blue spring.
I always use BP ultima 98 in the Sprite. On a long trip I once had to change to Shell. It worked out well, did run very smooth (but is more expensive)
Yes Nigel you are right; it is VERY difficult to make accurate measurements. I do not trust scientifically publications wit smooth graphics.


PS
Cederic. It is interesting how different batches(and their aging) of mix fuel react on my Stihl's.

I am very serious :(


Flip Br�hl

If you have some red springs try those instead.
Chris at Octarine Services

Agree with Chris--the M needles and your V3 would be better with red springs
You would only use blue if you were running H4 carbs to compensate for the lower air speed
William Revit

The blue spring is the softest 2.5 oz, . A soft spring gives a leaner mix. The red one 4.5 oz will give a richer mix.

Flip
Flip Br�hl

True----but

With HS2's on 1300cc the combination needs red (std) springs
You would only change the springs to blue if your carbs were bordering on too big--not the case here-
If you were running 1 1/2" (4's) then yes blue would probably be better but for what you have I'd say red---and then start on needle selection
The whole idea of spring choice is to reach full piston travel just at or slightly before the point where your engine develops it's maximum power
With the blue springs in your 1300 the pistons would be at full lift way too early-
What else is done to your engine, exhaust, cam ,air cleaners etc
William Revit

I've been beaten to it by someone with much more knowledge and experience that me but I'd just (as I often do) quote from the book, in this case the SU Tuning booklet. -

"It is best to use the red spring but if the carburetters are suspected of being on the large size for an engine then the blue should be tried. Conversely if the instrument is only just large enough, a stronger yellow spring might be required."

The 1275 carbs as standard are light blue springs.
Nigel Atkins

Willy,
you might be interested to reply to the OP on thread 'GM 3.4 SFI' in 'MGB engine conversions'.
Nigel Atkins

Post is slower than before the corona crisis. So I do not have red springs. I did get the M needle but did not fit them yet.

William asked; what else is done to your engine
1275, .60 overbore
Piper BP255
Maniflow 031 LCB and exhaust system
Peter Burgess for more low torque prepared head (big rimflow valves),
123 ignition 31 degrees max
SU HS2
Standard inlet

Yesterday I assembled beautiful 1 1/4 MED stub stacks. There is a big difference! it runs smoother in the low range. I thougt that they would give more power in the high range only.

Flip





PS, I am already 68 years a dyslectic and it is only the spelling chequer that prevents me from more faults. I have no problems at all if you correct me.
Flip Br�hl

My 2 bobs worth--
It 'should' work like this---
HS2 on a 1275--red springs
.060" overbore will make it run just a bit rich-
Headwork, Maniflow and exhaust will lean it-
So your combo wouldn't be far away from needing std mixture setup
The M needles and red springs would, should ,give you a very close to normal mixture, certainly close enough for a visit to the Peter
Every car is different and a roller session with Peter is the way to get the mixture spot on to suit your combo

Just thinking-If the substacks have made that much difference, maybe your aircleaner gaskets or an aircleaner or something might have been restricting the dashpot vent holes and throwing your mixture rich-------------?
You mentioned the ign timing wasn't quite right as well --ign timing doesn't normally effect mixture all that much but if it was way too far retarded it might show as a lean mixture, definately not as a rich mixture
Are your air cleaners nice and clean---
William Revit

This thread was discussed between 05/03/2020 and 21/03/2020

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