tr4 TR4 HS6 carb set-up

[Peter Cobbold]

JFerg,

+1 thats exactly why I like SUs.

With an exhaust wideband ( UEGO) AFR sensor and a camera to report piston lift it should be possible to tune as we drive.

 

Where a compromise is inevitable is between cruise economy at speed and,say, 3500rpm and pulling smoothly at wide open throttle at approx 1500 rpm. These two loads require similar horsepower and hence similar air flows. But cruise needs a leanish mixture for economy, while full throttle neeeds rich. But the carb can only provide one mixture at that air flow. So which one to tune the needle for, cruise or wot? Book profiles try to strike that compromise, so the needle tends to be leaner towards the thick end for cruise, and so too lean to be ideal for full load at low rpm.

 

There is liitle known way around this compromise. Set the needle rich top to bottom at wot. Then lean the cruise mixture with "back suction control" of the air pressure over the fuel in the float chamber. Here is how it is done:

http://www.fbekholden.com/forum/viewtopic.php?f=25&t=18810&start=45#p197886

Note: the description of the fuel level in the jet being lowered is wrong. The level stays fixed by the needle valve and float. It is the air pressure above the fuel that is dropped. Less pressure drop between float airspace and jet the lower the fuel flow.

 

(The rest of that long blog describes the exploits and engineering of Australian TR racer and supercharging guru, the late Eldred Norman )

 

Peter

Edited March 9, 2015 by Peter Cobbold

[JFerg]

Thanks, Peter.

 

SU's are a brilliant piece of engineering, something that should not really work and yet does. My admiration for Mr. Skinner is enormous. I'm intrigued to know how they ever fine-tuned them in the vintage period, when plug-chops were about the limit of technology. And how they got them to work in the first place, of course.

 

On my first excursion to the dyno some years ago, I'd marked off one piston in eighth inch increments in order to try to gauge needle position. I had 15 weight motorcycle fork oil in the dashpots. At full throttle, the pistons were bouncing all over the place, not only limiting performance, but spitting and blowing fuel vapour everywhere. Since then I have always run 50 weight engine oil in the dashpots. I know that this is "wrong" by every source, both credible and otherwise, but for me and my car, it works. My car is my sensible car. Whilst not quite a daily driver, it is a general purpose vehicle and is driven largely around town a couple of times each week. With proper damping in the dashpots, there's no apparent deficiency in performance, certainly no lags or lean spots on acceleration.

 

cheers,

 

JFerg

[TRnorm]

Peter, you mention a wideband AFR meter so i guess you have, or do, use one. Can i ask if you have used one where the lambda probe goes up the exhaust pipe and if so, is it any good.Appreciate that a boss in the downpipe is the right way, but with other problems at the moment I want to know if one up the exhaust is worth the (small) effort or not.

PS. I do have the 4.5oz red springs which i measured at 2.6" compression to be within a few grams.

Finally taken the needles out and these I find are BAM (not the SMs that I thought they were).

 

Booked in for a rolling road carb set-up for early April, but meanwhile have to get enough miles on the clock to get the engine run-in.

 

Norman

[Peter Cobbold]

Thanks, Peter.

 

SU's are a brilliant piece of engineering, something that should not really work and yet does. My admiration for Mr. Skinner is enormous. I'm intrigued to know how they ever fine-tuned them in the vintage period, when plug-chops were about the limit of technology. And how they got them to work in the first place, of course.

 

On my first excursion to the dyno some years ago, I'd marked off one piston in eighth inch increments in order to try to gauge needle position. I had 15 weight motorcycle fork oil in the dashpots. At full throttle, the pistons were bouncing all over the place, not only limiting performance, but spitting and blowing fuel vapour everywhere. Since then I have always run 50 weight engine oil in the dashpots. I know that this is "wrong" by every source, both credible and otherwise, but for me and my car, it works. My car is my sensible car. Whilst not quite a daily driver, it is a general purpose vehicle and is driven largely around town a couple of times each week. With proper damping in the dashpots, there's no apparent deficiency in performance, certainly no lags or lean spots on acceleration.

 

cheers,

 

JFerg

JFerg,

Whatever works well is working well enough! The oil only dampens the piston motion transiently, it wont affect the steadt running lift/air flow relationship. I wonder if the oscillation was not due to cam or manifold reversion flows but to an under-damped oscillation between lift force and the downforce on the piston.

I use EP 140 in the dashpot of my single 2"SU !! it works OK but I have not got round to tuning it properly.

Peter

Edited March 10, 2015 by Peter Cobbold

[Peter Cobbold]

Peter, you mention a wideband AFR meter so i guess you have, or do, use one. Can i ask if you have used one where the lambda probe goes up the exhaust pipe and if so, is it any good.Appreciate that a boss in the downpipe is the right way, but with other problems at the moment I want to know if one up the exhaust is worth the (small) effort or not.

PS. I do have the 4.5oz red springs which i measured at 2.6" compression to be within a few grams.

Finally taken the needles out and these I find are BAM (not the SMs that I thought they were).

 

Booked in for a rolling road carb set-up for early April, but meanwhile have to get enough miles on the clock to get the engine run-in.

 

Norman

Norman, I have one, from AEM, ready to fit ! Its going to be used not only to set up the SU but also to control the lean mixture continually at cruise. You need a wideband UEGO probe not a lambda sensor. It can be used up the exhaust but has to be pushed well in - foot or so - to be completely free form air sucked back in the tailpipe. There must also be no leaks in the whole exhaust run,all the joits must be gas tight. Any air leaks will give spurious lean readings. (This aplies to rolling road tuning too - they stuff a sensor up the tailpipe) Its best to measure nearer the manifold maybe 18 inches from the cylinder head. Weld on bosses are available to weld to an exhaust runner, and there are also clamp-on bosses to fit a drilled hole. The sensor is heated by the control box and will be damaged by liquid water/condensation if run cold. A tail pipe may be wetter site than nearer the engine.

Lots of expertise on here from actual users - Innovate devices seems to be popular, gives readings for a computer. But I think they all use the Bosch UEGO sensor.

 

Puzzling the SU pistons should be so stiff to lift with dampers in place but not with them removed. That needs sorting before rr. The carbs wont work right otherwise - downforce is critical to metering.

Peter

[Kiwifrog]

BAM needles are for the later spring mounted floating needle type SU's, I have a pair of ex Marina HS6 floating needle type of carb on my TR3A.

If the needles are really BAM and they are held in solidly without a spring mounting then it is a bit bizzare. You must have later carbs on your car not the origonal TR4A type. What is the code on the little aliminium tags on the carbs they should be AUD with fixed needles or FZX with floating needles

 

cheers

 

Alan

[peejay4A]

My HS6s with biased needles have AUD tags. They were purchased new. Weird.

Edited March 10, 2015 by peejay4A

[TRnorm]

Hi Alan,

My needles are spring loaded, biased towards the engine. But you're correct in that they are not originals. The car is Ex US and came with Strombergs. The carbs I have fitted were waxstat type - I think from a triumph 2500. They went to Burlin with the request to make them non-waxstat and to be jetted for a fast road tune TR4, and there were no ali tags - so that's their history. But I didn't understand the chronology of the needle evolution - so thanks for explaining that for me.

And Peter, that seems a fascinating project you are undertaking - I do hope you will be sharing it with us all. Even the less auto-technical of us understand how fuel injection and electronics has advanced the performance (in the widest sense) of our cars, but if we achieve a little of this whilst retaining our beloved SUs that's a really satisfying achievement. (Just found the AEM info on http://www.efi-parts.co.uk/index.php?productID=204&sent=yes - looks interesting and a fair price! )

And I wait wait patiently for your explanation as to how you are going to "....control the lean mixture continually at cruise..."! Some form of PID loop acting on the jet nut perhaps?

 

Great stuff

Norman

[Peter Cobbold]

Norman,

The back suction control using feedback from an UEGO sensor is outlined here:

https://supertrarged.wordpress.com/2013/05/06/tr6se-12-electronic-back-suction-control-of-su/

I had help from an expert with the electronics. It should be working in time for the IWE. Shall write it up for the blog, even if it doesn't work - I'm not for hiding negative results. I'm confident it will keep AFR within limits during gradual changes in load, but flooring throttle suddenly from cruise - not sure.

Cheers

Peter

Edited March 10, 2015 by Peter Cobbold

[Kiwifrog]

Norman

 

I have a setup very close to yours 2.2L engine, waxstat HS6's with TR4A head lightly worked and I run BBW needles, leaner than BAM at the bottom end and Richer at the top end. The car runs smoothly and with a good burn across the entire rev/power range

 

Check out the curves on mintylamb.co.uk which is where I simulated a number of needles before deciding on the BBW

 

Cheers

 

Alan

[TRnorm]

Impressive stuff Peter!

Norman

[TRnorm]

Alan,

I'll be looking at mintylamb (mintylamb!) and the finer points of needle profiles. But certainly encouraging to know a similar set up is working well for you.

 

Actually, now I've finally got the engine running (as opposed to stuttering and not running) I'm finding it is responding to the finer tweeking. But it does seem to me that the area of coincidence of the variables that has to be achieved for basic running is a lot smaller than is generally assumed.

Bit of a learning curve - as they say.

Norman

[monty]

Any SU carb queries then ask Andrew Turner, nothing he does not know about them.

Stanton Motorsports near Membury, Wilts have a rolling road & specialise in classics.

[Peter Cobbold]

Norman,

Do the pistons still need excessive effort to lift them manually with dampers in place ( #11) ? If so try running without the dampers in place. Apart from very sudden flooring the throttle the carbs should work reasonably without the dampers, if you feed the throttle in gradually.

I dont know which dampers were fitted to which carbs, but that might be the problem: wrong dampers

Peter

Edited March 11, 2015 by Peter Cobbold

[peejay4A]

Norman

 

I have a setup very close to yours 2.2L engine, waxstat HS6's with TR4A head lightly worked and I run BBW needles, leaner than BAM at the bottom end and Richer at the top end. The car runs smoothly and with a good burn across the entire rev/power range

 

Check out the curves on mintylamb.co.uk which is where I simulated a number of needles before deciding on the BBW

 

Cheers

 

Alan

Out of interest, what springs are you using Alan?

[Kiwifrog]

Hi Pete

 

I have AUC4387 (red) springs in them, I have not removed the waxstats, if they give me trouble I will do the 2 penny conversion on them but at the moment they seem fine with a nice light brown colour to the plug tips.

 

My carbs are coded for a 1750 Allegro but changing the needles and springs bought them into TR7 spec although I found the BDM needle a bit lean so changed to BBW, I guess this is because I run short Ram stacks on them.

 

Alan

Edited March 11, 2015 by Kiwifrog

[Chris59]

Hi Pete

 

I have AUC4387 (red) springs in them, I found the BDM needle a bit lean so changed to BBW, I guess this is because I run short Ram stacks on them.

 

Alan

 

 

Badfrog, get out of Alan, pleaaaaaaaaaaaaaaaaaaaaase !

[Richardtr3a]

Hi Norman

 

Sounds like you need a rolling road, but first a bit of a carb health check. It sounds to me like you have variable air intake, so those carbs aren't airtight ?

 

If you can get it running I recall that Southern Carbs at Wimbledon know their stuff. Ask for Peter if he's still there.

 

Regards

After having problems with some dud fuel, I took my car to Southern Carbs. They left me with the plugs getting very black in a very short time. At the IWE that year, Darryl Uprichard of Racetorations advised me to adjust the jets to almost fully weak position and it has been running much better since then about 4 years ago. i am still looking for an SU specialist in Sussex. There must be someone who still understands these jets and needles ?

[TRnorm]

Just to say Thanks to everyone - I have been reading all the recent help and suggestions, and taken them on board. But other than that I'm in a state of limbo as my Dizzy is away with Martin Jay as I wanted it to be beyond suspicion for when my rolling road session takes place.

Not to my total surprise, I was told with the authority of someone Who Knows, that what I had was the lowest grade of Chinese rubbish yet seen! I did have my suspicions as the timing mark was fluctuating considerably even after i got some form of reasonable tick-over, albeit at high revs. So fingers crossed, this may well make a significant difference once the totally new dizzy is installed and statically set-up.

I'll update on this and the rolling road tune up, as and when.

Norman

Edited March 16, 2015 by TRnorm

[Kiwifrog]

 

 

Badfrog, get out of Alan, pleaaaaaaaaaaaaaaaaaaaaase !

 

:D

[monty]

After having problems with some dud fuel, I took my car to Southern Carbs. They left me with the plugs getting very black in a very short time. At the IWE that year, Darryl Uprichard of Racetorations advised me to adjust the jets to almost fully weak position and it has been running much better since then about 4 years ago. i am still looking for an SU specialist in Sussex. There must be someone who still understands these jets and needles ?

 

I have said before, Andrew Turner knows all about SU's & was a great help to me a few years ago.

Cheers.

[MRG1965]

More interesting stuff - many thanks

 

Chris - I'm now wondering why I thought SM was the needle. I need to review were that came from. Might be that because of the cam.

The engine is number CT20 thousand and something. It has BP270 cam (Piper I think) and the later exhaust header (cast iron 2 into 1 type). I forget exactly what the exhaust is but it was basically a Moss straight through(?) I've measured the head and reckon the CR might have been upped by no more than 0.5.

The needle/jet centralisation seems fine. With the jets fully in (lean), both pistons fall freely at the same rate and hit with that nice "clonk".

(Think I've just remembered why SM. When I sent the carbs away to Burlin 20 yrs+ ago for a full refurb (but only fitted last year) I asked for them to be jetted for a Fast Road set-up. They never confirmed the detail but because of the problems I'm now having I checked the jet dia (0.1") and the needle at 3 stations and concluded that it was a SM needle.)

 

Mark - interesting about what you experienced; similar symptoms yet as I indicated to Chris, I'm certain there is no binding twix needle and jet?!

I was puzzled about "checking the jets are fully up". Are you saying that your car runs with the jets fully up (lean)? Whilst I did raise them to bridge level to check the centralisation, I then lowered by 12 flats (2T) for the initial setting that I understand is the starting point that should allow the engine to run.

 

One other thing I have noticed that doesn't feel right is that with the dampers screwed in it takes quite an effort to manually push the piston up - real effort that I find difficult to think could be overcome by the suction in the upper chamber. Yes - its has Penrite SU carb oil in the pots and of course with the damper withdrawn, or with the oil removed , the piston rises with light finger pressure. (So no binding there i think.)

Recollections anyone on the force needed to lift the pistons?

 

Meanwhile - off to Halfords for some Wynn carb cleaner for a leak-test later today.

Thanks again

Norman

Hi Norman, found the cause of my carbs needing more than 12 flats.

 

Needles in my carbs had been incorrectly installed and needed the tophat soldering on to the needles and to stop them dropping out of the pistons, soldered them in this afternoon, adjusted to 12 flats and started perfectly.

 

Mark

[TRnorm]

Thanks Monty and Mark,

After managing to get it running only with >12 flats I too have now got it back to the 12F, but still have the very high idle. I don't think its an air leak as seems the most popular diagnosis, but this weekend I fit my Distributor Doctor dizzy and will see Whats What after that. Now it is running I'm happy with a slower incremental approach.

Norman

[CliveG]

After having problems with some dud fuel, I took my car to Southern Carbs. They left me with the plugs getting very black in a very short time. At the IWE that year, Darryl Uprichard of Racetorations advised me to adjust the jets to almost fully weak position and it has been running much better since then about 4 years ago. i am still looking for an SU specialist in Sussex. There must be someone who still understands these jets and needles ?

Just over the border in Hampshire is Tom Airey. Old school, very knowledgeable. Did a great job on my 3A.

http://aireytuning.com

Clive

[TRnorm]

Today my errant car visited the talented Peter Baldwin and his amazing rolling road in Wimpole, Cambridgeshire.

 

Followers will recall that I did get my TR up and running, of sorts, with the help of the contributors to this topic. Nevertheless,It arrived still running rich, unable to idle at less than 1450 rpm, and gave an initial CO2 of 8.5%.

After a few adjustments to get it running and idling more sensibly (700rpm) it was indicating about 105bhp.

After a fair bit of further refinement and running under various loads and speeds, and a change to slightly weaker needles, it was giving 118bhp with the rather small and nasty air filters as fitted. But it was still running a tad rich. Despite that, the CO2 was 2.5% and the Hydrocarbons a really low 180.

All the timing was tweaked and it was good to see they gave the BTDC figures claimed by Matin Jay for his rebuilt Dizzy.

Next, removing the air filters upped things to 125bhp but it was now a tad lean. So for now the filters are back on.

 

The next visit to Peter will be with some decent air filters - and an on-load "tune-up" of the timing might get us nearer the 130bhp level (it was said). (Perhaps without a change to needles or perhaps a very slightly richer pair.)

 

The engine now pulls more strongly and over an extended rev range (most noticeably at lower revs). And, as I had hoped, it felt smoother and quieter (although still masked, I think, by some remaining propshaft vibration).

 

For this crucial part of my cars fettling I have to thank Mike M-D for recommending Peter Baldwin and providing the other half of our two car convoy! Not forgetting either, his reassuring body language (of one who's car it isn't) when it was hitting peak power and sounding like the engine room of the Great Eastern.

 

In conclusion I would like to be able to say I now understand why I had so much difficulty setting up the SUs - but in reality I cant, other than to say it seems you need a rolling road and someone with a vast history of setting them up. Then it appears relatively simple.

 

Still loads more to do - but getting there.

Thanks everyone.

Norman