What needles with Newman PH1 in 4 cyl TR engine?

[BlueTR3A-5EKT]

What needles with Newman PH1 in 4 cyl TR engine?

If you have a wet liner TR 4 cylinder engine (TR2-4A) plus Morgans

And you are running a Newman PH1 cam  

And are using 87 mm pistons  

And you have minor head modifications  

And are using SU H6 or HS6 carbs with red springs.

 

What needles profile are you using?

I am running RH and find them too rich across the range, even though the tick over mixture is correct.

 

[Drewmotty]

My engine is a similar spec and I found that the SM was too lean at the mid/top end. RH sorted it out. 

[stuart]

16 minutes ago, BlueTR3A-5EKT said:

What needles with Newman PH1 in 4 cyl TR engine?

If you have a wet liner TR 4 cylinder engine (TR2-4A) plus Morgans

And you are running a Newman PH1 cam  

And are using 87 mm pistons  

And you have minor head modifications  

And are using SU H6 or HS6 carbs with red springs.

 

What needles profile are you using?

I am running RH and find them too rich across the range, even though the tick over mixture is correct.

 

You could try the Minty Lamb comparison chart http://www.mintylamb.co.uk/suneedle/

The site isnt as easy to use as it was though, 

somewhere I have an SU needle comparison book that Burlen used to produce, https://sucarb.co.uk/catalogues-manuals-books/su-needle-profile-chart.html,

Stuart.

Edited April 3 by stuart

[TR4Tony VC]

I recall that I was using SW needles with a similar cam years ago in my 4a. SX was richer ? 
 

Regards

Tony

[Drewmotty]

Looks like the SX will be a bit leaner at the bottom end so may suit you. 

[BlueTR3A-5EKT]

All helpful thank you.

 

[Lebro]

Listening with interest !

Bob

[Rob Salisbury]

This tip was given to me by a motorcycling friend who races a Manx Norton 500, carbs don't care if the needles are round or D shaped, take a pair of needles that are too lean and a needle file and progressively form a flat along the length to richen up until you get the desired result, ideally this needs to be done on a rolling road or using a Lambda sensor or a CO sensor.

Cheers Rob 

[silverfox4]

+1 for Bob - I'm listening.  I'm using SM at the moment but have SW and new red springs ready to test for the warm weather.

Cheers, Alf

[Motorsport Mickey]

On 4/3/2025 at 10:45 AM, BlueTR3A-5EKT said:

What needles with Newman PH1 in 4 cyl TR engine?

If you have a wet liner TR 4 cylinder engine (TR2-4A) plus Morgans

And you are running a Newman PH1 cam  

And are using 87 mm pistons  

And you have minor head modifications  

And are using SU H6 or HS6 carbs with red springs.

 

What needles profile are you using?

I am running RH and find them too rich across the range, even though the tick over mixture is correct.

 

Dampen down the piston response Peter, Try a large penny washer dropped inside the piston over the cowl, the extra weight will make the piston rise slower ..ie weaker across the range. Variation of the weight can be done by trimming outside dia as required.

Mick Richards 

[Ian Vincent]

I can’t be certain Peter but I’m pretty sure I have SY needles in my HS6 carbs on an engine that’s pretty similar to the one you describe, i.e. Newman PH1 cam and 87mm liners. 

Rgds Ian

[Chris Hubball]

I am running my Tr4 with 87mm pistons Piper Yellow Cam extractor manifold and Pete Burgess modified cylinder head I have SL needles fitted giving good performance and fuel economy.

Cheers Chris

[Lebro]

I thought I was using SM, but have just checked, & I have RH (TR3 - "rich) fitted at present. I have two sets of SM in stock. 

I am going to try a pair of SW as they seem similar at low vacuum, then weaker in mid range, where most cruising is done, then they richen up at bit when flat out.

This to try to improve fuel economy which I have noticed had gone down since the engine re-build.

Bob

 

Edited April 6 by Lebro

[RogerH]

Can that bottom line be explained - low to High vacuum

I would have thought that at tick over you would have a high vacuum and at WOT it would be a low vacuum.

I suppose it is where in the manifold it is being measured

 

Roger

Edited April 7 by RogerH

[RobH]

 An SU is a constant-depression carb so the vacuum at the jet shouldn't change much over the operating range.  That number must just represent raising of the needle by the piston - maybe the test rig used a vacuum to do that. 

[RogerH]

Thank you.

 

Roger

[Ian Vincent]

On 4/7/2025 at 9:30 AM, RogerH said:

Can that bottom line be explained - low to High vacuum

I would have thought that at tick over you would have a high vacuum and at WOT it would be a low vacuum.

I suppose it is where in the manifold it is being measured

 

Roger

Hi Roger,

I have a virtually identical graph which I produced myself on Excel using data from an old book that I have called Tuning SU Carburettors (including full needle charts).  It was originally published in 1970.  The needle charts list the diameter of the needle against the various stations of the needle, from which it is easy enough to work out the anulus area.  Here is a copy of my chart.

From this you can see that the "Low to high vacuum" has nothing to do with it.

I switched to SY needles from SM after having the car tuned by Revington on their rolling road and Dan advised me that it was running slightly rich at low revs.  I reasoned that with the SY needle having a virtually identical profile at the lower end but being richer at the top end would provide a better balance.  My fuel economy on long runs is up in the low to mid thirties so I'm happy with it.

Rgds Ian

PS I added the lines separating the operating ranges on the needle from data that I picked up elsewhere (I think).

 

Edited April 8 by Ian Vincent

[BlueTR3A-5EKT]

This all very helpful.

This week I turned both jets up by one flat and the car is running sweeter.  The smoke on acceleration has gone too.    So a lot of the issue I had was set too rich.

I have just done a steady 75 mile drive cruising at 3000-3500 rpm and stuffed on  the M25 for 10 miles at 30-50 mph.   Economy is in the high 20’s low 30’s

[Lebro]

SW needles arrived (one as new from ebay (cheap) & one from Burlin (not so cheap, but cheaper than others).

Cleaned up carbs, & did the “drop” test, ok, fitted SW needles (to try to improve fuel consumption).
Found rear carb fuel level rather low in jet, so shortened the float jet housing seat by around ½ mm (no washer to remove).
Wound jet up to be flush with bridge. (front jet was already there). Ran engine till warm, check "suction" on carbs they were well balanced already.
Checked mixture with colour tune, 1 & 4 were slightly rich, 2 & 3 were around correct, so no further adjustment made.

Road check next - watch this space.

Bob

[Lebro]

Road test went ok, seems more responsive on initial movement from rest, The warm up time was quick, (but it had been running less than 2 hours previous, so proper test from cold another day). Drives nicely with no hesitation, so far so good, question is what will fuel consumption be - time will tell.

Bob

[silverfox4]

Thanks for that Bob. Now decided that I too will switch to the SW in a few weeks then. would be interesting to hear about your consumption and plug colour.

Cheers,

Alf

[RogerH]

Hi Folks,

I have Newman PH1

Extractor manifold

87mm pistons

I thought I had TW needles which sounded about right  !!

But upon looking just now I find I have KO needles  - it that good, bad, or ugly.

Consumption about 30mpg (it noticeable dropped upon fitting the PH1)   The plugs and exhaust are always black and sooty.

However it drives well with good response from 60mph upwards.

Roger

PS - just noted on minty Lam that the KO is very similar to the SW and TW needles

Edited April 22 by RogerH
update

[RogerH]

How does one interpret the MintyLamb graphs.

It all looks very pretty but is gobbledegoop to me.

 

Roger

[Peter Cobbold]

A needle that is correct at cruise will AT THE SAME POSITION give a richer mixture when the butterfly is more than 30 deg open.  At cruise and small b'fly angles the pulses from ivs do not reach the jet, so cam profile has little effect on the correct (cruise) needle profile. Under acceleration and b'fly > 30 deg open the iv pulses will reach the jet and will richen the mixture. If the needle is tuned at wot, as on a RR, then the chances are it will be too lean at cruise. Best tune on the road at cruise with a UEGO in the exhaust and a small camera to measure piston lift. Then confirm it richens at wot to say AFR 13 or richer.

More here: https://supertrarged.wordpress.com/2017/07/10/how-does-an-su-carburettor-work/

The pulsing effect is known as 'mixture spread'

Peter

 

Edited April 23 by Peter Cobbold

[silverfox4]

Bob, a small update from my side as I walk through  these needle and general SU setup confirmation.

The first thing is that both chambers seem to fail the drop test, even after interchanging  - they are too fast, maybe 2 secs at best.  

I changed out the old springs for new "red" and find a slight difference in length though both check out at circa 127g as best I can measure, so I'm assuming there will be no difference with the new springs, right?

 

Cheers,

Alf