Which needles?

[Alan Cochrane]

Hi Everyone

I'm looking for a bit of advice on what is considered the best needles for HS6 carbs fueling a tuned 2.5 six. The engine has a gas flowed "stage 2" head, fast road cam and a SS tubular extractor manifold. The carbs have BAE needles fitted.

This set-up has been in my GT6 for the last twenty plus years and has generally been good although I've never managed to get the idle speed down below 900rpm.

I've finally decided to rebuild the carbs and I'm now wondering if these are the best needles for this setup. I'm sure I'm not the only one running this setup, so all advice gratefully received.

Cheers

Alan

[Rodbr]

Hi Alan,

In my experience it is virtually impossible to define accurately what needles to use. Even if someone has the same tuning items fitted each engine will behave in a different way, due to tolerances. There is a guy from my area that Hillclimbs a GT6 that could perhaps help with advice. 

As a first step which is potentially an expensive one but depending on your budget may be effective.

Go to Burlen Services and go through the needle chart and pick pairs of needles close to yours which give the upper range of dimensional values close to what you have. Get a pair of Colourtune units install and go play and you may be lucky and given time, and an uncertain number of needles you may get close to what you want.

I cash is not an issue find an SU company that can put the car on a rolling road pay up and get the result you want reliably. Just do a Google search for this service and suitable Companies will come up. Suggest that you ask for approximate cost and time needed. Before going make sure that all other systems are up to snuff or you may spend rolling road time chasing faults. i.e. fuel delivery, ignition etc etc/

Hope this helps.

Persinally I use four colourtune units to get a picture of the whole system and it works very well to get the closest match. I have always used my ear to set air balance and then check with a flow meter usually get a very accurate result as shown by plug colour.

There is an older version of this book which is worth having as follows :

SU Carburettors Tuning Tips and Techniques
By G.R. Wade

 

Drop me a pm and we can talk it through.

Best regards

Rod

 

Edited October 31, 2018 by Rodbr

[Lebro]

IMO  Colourtune's are very good for checking mixture at tickover, & for checking the balance over the 4 (or 6) pots (I use 4 of them myself).

But, they won't be of much use to indicate the mixture under load, ie throttle open more than at tickover, unless you can arrange for a camera under the bonnet !

 

Bob.

[RogerH]

Hi Alan,

            air leaks around the carb butterflies will reduce you capability to get the tick over revs where you want them. 

Moss and the others do rebuild kits that work well. My SU's had  very worn spindles but the body had no wear. The kit had the desired affect.

How is your ignition timing.  The wrong setting (too advanced I think) may cause a higher tick over.

 

Roger

[DRD]

Hi Alan,

I think these are the recommended needles for that tune of engine. I have have something similar and use BAG needles which are slightly leaner at lower throttle openings but get richer higher. I get a reasonable but lumpy tickover at 800rpm. The 'Minty Lamb' website was great for comparing needle profiles, unfortunately it doesn't exist anymore. However I do have some printouts of several of the SU needles that are suitable. I can copy them and send them to you if you are interested.

BTW I agree a rolling road is a good solution, but I've managed OK by using a %CO meter, carb balancer and timing light. Then driving it a bit and checking the plugs.

Daz

[RobH]

Burlen sell a needle chart pamphlet:

http://sucarb.co.uk/su-needle-profile-chart.html

or there is limited information here (as it is a early version of the book) :

https://tecb.eu/onewebmedia/Tuning_SU_Carbs.pdf

 

There also seems to be some needle selection software available (I haven't tried it so I don't know if it is any good) :

http://www.winsu.co.uk/

Edited October 31, 2018 by RobH
updated

[Alan Cochrane]

Hi Everyone

Thanks for the advice and I agree with most of it. I also use colourtunes(2 of), a flow meter and gas analyser. 

I’ve already found one air leak at the servo vacuum outlet and the rear most carb jet does not return to it’s choke off position when the choke is pushed all the way back in. So two reasons for poor idling already.

I’ve ordered a full rebuild kit from Burlen and new vacuum hose so it’ll be interesting to see what difference that makes. The carbs are a bit of a Frankenstein. The bodies, float chambers and jets are from a 2500S saloon and the bells and pistons from a Rover SDI. Reason being the very tight under bonnet space available for the front carb. Even with this setup I had to cut down the dashpot necks and shorten the dampers!

The piston springs are probably wrong as well coming from the SDI, so I’ve also ordered red springs from Burlen.

Anyway plenty to be getting on with over the winter. 

Thanks again

Alan

 

 

 

Edited October 31, 2018 by Alan Cochrane

[TR NIALL]

Hi Alan what Car are you running that Set Up in?

Sorry I see it’s a GT6.

Edited October 31, 2018 by TR NIALL

[Peter Cobbold]

My solution - not yet implemented- is to tune it on the road while driving. UEGO wideband gauge in the exhaust for mixture and a remote camera to measure piston lift.

Note that the mixture at a given needle position ( piston lift ) is not fixed.  It depends upon whether the butterfly is open more than 30 degrees. Less than 30 deg kills pulsing of pressure from the iv opening reaching the jet. More than 30 deg b/f opening the pressure pulses will richen the mixture. For example with say 3 points up the needle you can get a lean cruise mixture at part throttle and a rich mixture at full throttle and of course lower rpm.   SU Co called this effect " mixture spread"

The effect of pulses is lowered the bigger the manifold balance pipe.

So I would tune the needle by measuring at part throttle with b/f always less than 30 deg open up the rpm range. Then check the full throttle mixture is not excessively rich. There is alot more leeway with rich mixtures.

Peter

[John L]

Do you have Biased needles? and or waxstat jets?

In the Moss parts book they recommend BAE for biased needles, 6AM is listed as a richer one with all the engine mods exhaust, filter,cylinder head, camshaft.

But for a fixed jet they recommend SM needle.

Hope this may help

John

[TR NIALL]

Hi Alan,I’m running a 2.5 CP with hotter Cam in a Sixfire using a 2.5s Manifold and Dolly Sprint Carbs the needles I’m using are BDM with Yellow Springs and the bigger Dolly Sprint KNs with StubStacks fitted inside and it’ll tick over at 700rpm and drive up through the gears up to a very fast max speed.

[oldtuckunder]

When you want to get it right there are only two three options, luck, a lot of time on the rolling road, or buy a wideband sensor(s) with data logging capability. The latter will work out way cheaper in the long run!, and you'll learn a lot in the process.

Alan

Actually I do use a Rolling Road as well, but only to get the final tweak and some real numbers.

Edited October 31, 2018 by oldtuckunder

[DaveR]

A number of years ago I used the 2.5 Litre in my wife's Gitfire, GT6 Convertible she had at the time. I used the S head skinned, extractor exhaust, Mk2 cam and HS6 carbs. After lots of trials with different needles and springs I settled on BAE with green springs. The BHP was around 125 - 130. No problems with tick over and the performance matched the indicated BHP figures.

Dave 

 

[Alan Cochrane]

Well I've not managed to do anything yet because we've now bought a holiday home that needs some TLC. However tomorrow will be a garage day as will next Tuesday so happy days are back, at least temporarily. In the meantime my rebuild kit has arrived from Burlen. 

I have managed to get my spare inlet manifold machined out to accept the HS6 carbs directly. The inlet ports on my manifold have now been enlarged from 1.5 to 1.75 inches. Has anyone else done this in order to get rid of the sandwich adaptor plates?

The machine shop even smoothed out the inner casting, all for £30. The manifold is an odd setup with only two stud fixings available for the original stromberg carbs-

 

The carb mountings are even different shapes for some reason. 

Anyway I will hopefully start the strip down tomorrow.

Cheers

Alan

 

[Peter Cobbold]

8 minutes ago, Alan Cochrane said:

Well I've not managed to do anything yet because we've now bought a holiday home that needs some TLC. However tomorrow will be a garage day as will next Tuesday so happy days are back, at least temporarily. In the meantime my rebuild kit has arrived from Burlen. 

I have managed to get my spare inlet manifold machined out to accept the HS6 carbs directly. The inlet ports on my manifold have now been enlarged from 1.5 to 1.75 inches. Has anyone else done this in order to get rid of the sandwich adaptor plates?

The machine shop even smoothed out the inner casting, all for £30. The manifold is an odd setup with only two stud fixings available for the original stromberg carbs-

 

The carb mountings are even different shapes for some reason. 

Anyway I will hopefully start the strip down tomorrow.

Cheers

Alan

 

Alan, Are you sure that manifold will fit the head?  Early manifolds and heads had ports closer together. Cant recall the details.....but that manifold looks like one I have that wont fit my TR6 heads.

Peter

[graeme]

7 hours ago, Alan Cochrane said:

Well I've not managed to do anything yet because we've now bought a holiday home that needs some TLC. However tomorrow will be a garage day as will next Tuesday so happy days are back, at least temporarily. In the meantime my rebuild kit has arrived from Burlen. 

I have managed to get my spare inlet manifold machined out to accept the HS6 carbs directly. The inlet ports on my manifold have now been enlarged from 1.5 to 1.75 inches. Has anyone else done this in order to get rid of the sandwich adaptor plates?

The machine shop even smoothed out the inner casting, all for £30. The manifold is an odd setup with only two stud fixings available for the original stromberg carbs-

 

The carb mountings are even different shapes for some reason. 

Anyway I will hopefully start the strip down tomorrow.

Cheers

Alan

 

Alan,

That manifold look more like a Triumph 2000 or GT6 with smaller 1.5 inch carbs.

Cheers

Graeme

Edited November 9, 2018 by graeme

[TR NIALL]

That looks like a GT6 Manifold and is made for Strombergs you can fit the 13/4 SUs by enlarging the holes on the Carb Body but it’s s bit iffy your best bet would be to get the Conversion Adaptor Plates that we’re available but I’m unsure where you can get them now you may also need longer Mounting Studs as the Priginal are to short,don’t be afraid to use the Sandwich Plates as they stop heat transfer.

If I was you I’d go on the hunt for a 2.5s Manifold that was originally made to take the 1”3/4”SUs and gives a much better Flow due to its Design.

[TR NIALL]

10 minutes ago, TR NIALL said:

That looks like a GT6 Manifold and is made for Strombergs you can fit the 13/4 SUs by enlarging the holes on the Carb Body but it’s s bit iffy your best bet would be to get the Conversion Adaptor Plates that we’re available but I’m unsure where you can get them now you will also need longer Mounting Studs as the Original are to short,don’t be afraid to use the Sandwich Plates as they stop heat transfer.

If I was you I’d go on the hunt for a 2.5s Manifold that was originally made to take the 1”3/4”SUs and gives a much better Flow due to its Design.

if it’s for your GT6 you’ll have to alter the Bonnet as you’ll have closing issues.

 

Edited November 9, 2018 by TR NIALL

[DaveR]

Due to the location of the throttle bracket mounting threaded hole, it has short inlet pipes, no up angle and no heater valve the manifold shown would appears to be a 2 Litre Vitesse Mk2, not the GT6. It would normally take 150CDs Strombergs. 1.5" carbs. The head porting is the same as the UK spec TR5/6.

When fitting HS6 carbs on a GT6 you have to used the short dashpot type e.g. Used on the Dolomite Sprint.

Dave

[Alan Cochrane]

Sorry for the confusion over the image. It is a GT6 manifold but not mine unfortunately.  I was being lazy since I didn't have an image of mine to hand. I only used it to illustrate the different carb mounting flanges.

The saloon manifold will not fit because it's sloped upwards towards the carbs to counteract the engine being canted over by 9degrees IIRC.

I have the sandwich plates but sideways space is a bit limited once you add in the air filters and fuel pipe. I have now managed to make the sandwich plates redundant by having the inlet holes bored out to 1.75 inches and here's the proof:-

 

I had to to carefully measure all around the rear of the flanges to ensure there was enough "meat" to allow the enlargement.As you can see there was. This manifold rather puts my existing one to shame. It was only £35 off Ebay and someone has spent a lot of time polishing it up!

Cheers

Alan

[DaveR]

Sorry to disagree it's a Mk2 Vitesse manifold as it has a small tapped hole near the left hand water outlet. This takes the throttle bracket. The Mk2 GT6 has a different throttle arrangement and this hole is just not there. It can be used on a Mk2 GT6, you just don't fit the bracket.

Dave

[Alan Cochrane]

Dave 

Thanks for the info. That means that my modified manifold and also the one on my GT6 for the past 32 years is a Vitesse manifold. As far as I know the one that came with the car was original and was still sporting Strombergs when I bought it.

My GT6 was built in 1971 the same year as Vitesse production ended. Triumph probably used up any remaining stock on other models where possible. 

Every day's a school day!

Cheers

Alan

[DaveR]

Alan,

It's not a problem with the GT6. But if you obtain a GT6 Mk2 manifold and try to use it on the Vitesse Mk2 you normally find no hole for the throttle cable bracket.

On my wife's Gitfire I used the blocks and bored out the inlets to take the short dashpot 1.75" HS6 carbs. It's a shame that the 2500s inlet manifold is angled up as it's longer pipes help the gas flow at lower RPM. As you may know the 2500s saloon needles are far too weak with the a high CR and cam with more overlap. The Rotoflex couplers handled the extra power and torque ok. It was/is a very rapid car but with a very hard suspension. After many years of use we sold it as we wanted more comfort due to our age! Hence a TR7.

Keep up the good work.

Dave