SUs and needles for 87mm pistons

[anotheralan]

Many years ago I rebuilt my early TR3 engine with 87mm liner/piston upgrade, a hi-port head from a 3A (unmodified) , H6 carbs and fast road cam from Moss TT1004.

It has always run rich. It is way beyond time to do something about it!

I start from the position of ignorance so please feel free to chip in. I have put some thought into it though.

By my calculations the cc is increased to 2188 from 1991 and the compression ratio calculated 9.8 or thereabouts. The carbs now have 10% more CFM whistling down the throat with a consequent increased depression (not in me, in the carb) for any given engine speed. So I can't really expect the same needle to be right. Evidence is I need something to weaken the mixture through the range.

I have considered trying the SL needle, but that is a stab in the dark.

My car is closer to TR4A CFM, although exceeding 4A displacement CFM by approx 2.5%, but without the HS6 carb and its metering needle.

I have compared the standard needles, SM in the H6 with TW in the HS6, and with H6 SL as shown in the metering tables. The size difference at each of the 14 points in 1/10000" is as follows, +ve difference being leaner.

TW SL

01 00 00

02 00 00

03 10 05

04 10 05

05 15 12

06 27 08

07 36 05

08 40 05

09 40 05

10 40 04

11 32 05

12 30 06

13 30 00

14 30 00

 

All three needles are the same low down (idle) but the TW (4A) needle is a far greater difference (leaner) at increasing piston rise compared with the SL. At full throttle the SL is also no leaner whereas the TW is still considerably leaner.

There is more to it than my simple observations but I have to start somewhere. I considered swapping to HS6 carbs and manifold but I understand the S stands for short version of H6. Is this really necessary expense?

So, I am open to suggestions, experience that might be out there. I can't think I am the only person to have fitted 87mm pistons. I did see one member had fitted HS6 with 87mm.

 

bring it on.

 

Many thanks in anticipation and a little trepidation

Alan

 

 

[Lebro]

The HS6 carbs have a much better choke arrangement. but, as you say they are shorter, so really the longer 4A inlet manifold should be used to bring the total inlet tract length back to where it was. Can't help with the needle choice though.

 

I run a standard 3A engine (1991cc) but with HS6's using SM needle's & 4A manifold.

I get 30 MPG "around town", & have had up to 41 MPG on a long run.

So it can't be far out.

 

Bob.

[Mick Forey]

Since you have a non-standard cam and carb set up I recommend you take the car to a rolling road, preferably somebody with lots of experience with SUs. They will set up the mixture across the rev range and the timing to go with it. It is worth every penny to have a car producing lots of torque with no hesitation and good fuel economy. I took mine to http://www.mg-cars.org.uk/peterburgess/indexstart.html. Yes, he is an MG man but he tunes TRs and anything with SUs. I know he is too far away from you but it gives you a clue as to the type of person you need.

 

Mick

[anotheralan]

Thanks both

Bob, you seem to have the obverse of me, HS6 with H6 standard needles for 1991cc engine, so maybe i will try the standard TW HS6 needles in my H6 carbs. I would think your economy is down to the needle choice being right for the capacity. Will the obverse work? watch this space.

Mick, I may end up there but will see if something simple solves the richness issue without compromising performance. Last time I went for rolling road set-up was with Cambridge Motorsports, just after completing rebuild in 2000. They ran it up and said that it was set up exactly as they would have done. Perhaps i was not specific in identifying mixture as an issue but you would have thought............

 

Thanks for your responses. Perhaps somebody with 87mm change is yet to come forward.

Alan

[Hamish]

Alan

I have a 3a with 87mm with a 4 head and intake manifold with h6 carbs without filters and very old (1970s) cam and 4 branch manifold.

 

But Im not near the car ( 250miles away) to tell you the needles.

But also this spring my rolling road chap sorted the mixture as I went from carb trumpets with gauze to without thus he hand polished the needles for a smooth torque curve.

 

I also cant tell you about economy as I never check it esp as I do the odd sprint and hillclimb Reving the ars# off it.

 

The red line is the gear change indicator isnt it ?!

[anotheralan]

Alan

I have a 3a with 87mm with a 4 head and intake manifold with h6 carbs without filters and very old (1970s) cam and 4 branch manifold.

 

But Im not near the car ( 250miles away) to tell you the needles.

But also this spring my rolling road chap sorted the mixture as I went from carb trumpets with gauze to without thus he hand polished the needles for a smooth torque curve.

 

I also cant tell you about economy as I never check it esp as I do the odd sprint and hillclimb Reving the ars# off it.

 

The red line is the gear change indicator isnt it ?!

HoHo

Out of my league really Hamish. I just want any friends following me to not need the ventolin. I don't have any friends in front of me, by definition.

Alan

[Hamish]

Alan

Its not at all. Its very modest.

I have 116bhp at the flywheel thats all.

Keeps me in the <130bhp/tonne class.

 

Its not like these 150 - 180 bhp tr4 s that I lust after

 

Ps

Just a thought after my gauze / no gauze experience.

Do you have air filters ?

Are they restricting the flow.

Try it without as that would lean out the mixture

And a no cost test.

Edited June 4, 2018 by Hamish

[Peter Cobbold]

Alan, Principles of operation are here: https://supertrarged.wordpress.com/2017/07/10/how-does-an-su-carburettor-work/

Note that the depression is constant, fixed by the piston spring and weight, so running more air through simply lifts the piston more.

However you wont use more lift unless you have started driving harder as air consumption depends upon hp demand. Your concern about more air flowing will only affect the tip of the needle. So, what to do. I'd check the pistons fall correctly ( not stciking) and the correct srpings are in place ( kitcehn scales if the paint has worn off). Then start with weak road needle and see how it goes mpg-wise. If it stumbles upon opening the throttle fast from cruise at say 1500-2000 rpm try a thicker oil in the dashpot. If that doesnt work take about 1 thou off the needles over the first 3/8 inch of an inch ( micrometer , drill, emory paper.. And try again. That region is critical for mpg The mixture is much more forgiving at wot and higher rpm. But a road car uses the pointy end of the neelde for only ca 5% of the time so mpg hardly touched if its rich up there.

And the old adage, to tune the carb first set the timing is also important for best mpg. If the vac adv capsule isn't working you cant get the best from a leaner mixture.

Peter

 

all the above assumes the fuel level in the jet is a few mm below overflowing.

[ianc]

Alan - you are some 13 miles from Revington TR in Middlezoy. A couple of hours with Dan & Carl should sort out your car - they have the rolling road and SU needles, and an immense amount of experience. And it's not necessary to flog the car on the rolling road to sort out the problems.

Ian Cornish

[greasemonkey]

Alan - have a look at this previous topic - may be useful..

 

https://www.tr-register.co.uk/forums/index.php?/topic/64097-4-pot-carburetter-needles/

 

Phil.

[Richardtr3a]

After reading this thread I had my carbs and ignition set up by a local classic car workshop. They found that the vacuum adv/ret had petrol in it. This must mean that the fuel level in the carb is too high and this must contribute to my low mpg. I have stay up floats and viton tipped valves.

 

Is there any other problem that could cause fuel in the diaphragm and will it be damaged ?

 

Thanks

 

Richard

[Peter Cobbold]

After reading this thread I had my carbs and ignition set up by a local classic car workshop. They found that the vacuum adv/ret had petrol in it. This must mean that the fuel level in the carb is too high and this must contribute to my low mpg. I have stay up floats and viton tipped valves.

 

Is there any other problem that could cause fuel in the diaphragm and will it be damaged ?

 

Thanks

 

Richard

Richard, There should be a vapour trap in the vacuum line that will condense petrol vapours before they get to the v-a capsule. Peter

[Richardtr3a]

New parts ordered Thanks Peter

[Fireman049]

Hi Richard ~

 

Here's the vapour/fuel trap as fitted to my 3A. Make sure the trap is fitted pointing upward towards the distributor

as near vertical as possible.

 

Tom.

Edited June 16, 2018 by Fireman049

[Richardtr3a]

Thanks for the photo. Will this make a new capillary make a difference to my mpg.I have never had a trap but my mpg has never been very good.

 

Thanks

[Fireman049]

Hi Richard ~

 

As far as I'm aware this modification should have no real effect on your fuel consumption but will safeguard your distributor.

 

Tom.

Edited June 16, 2018 by Fireman049

[Fireman049]

Anyone contemplating fitting an Albertronic '123' distributor, then fitting a vacuum pipe with the vapour/fuel trap is essential.

Any fuel drawn into the '123' will render it useless.

 

Tom.

[Richardtr3a]

Sorry to be back on a subject started by someone else. But this evening I removed the plugs to check the mixture and they were covered in black deposit. They are Iridium and the car was running well, but it is much too rich. I put two gallons into an empty tank. I have driven 17 miles and there is only one gallon left. I use a home made dipstick. I am pressed to get it ready for Lincoln.

 

I cleaned them all off and will give it a trial run tomorrow morning.

 

Please give me some advice on a weaker needle than the SM.. The only upgade to my 3A is the new pistons 30k miles ago now 2,138 cc The book supplied by Burlen shows a weak needle SL. Has any one used this needle.

 

Thanks

[Peter Cobbold]

Sorry to be back on a subject started by someone else. But this evening I removed the plugs to check the mixture and they were covered in black deposit. They are Iridium and the car was running well, but it is much too rich. I put two gallons into an empty tank. I have driven 17 miles and there is only one gallon left. I use a home made dipstick. I am pressed to get it ready for Lincoln.

 

I cleaned them all off and will give it a trial run tomorrow morning.

 

Please give me some advice on a weaker needle than the SM.. The only upgade to my 3A is the new pistons 30k miles ago now 2,138 cc The book supplied by Burlen shows a weak needle SL. Has any one used this needle.

 

Thanks

Richard, Has mpg got really bad since the classic garage worked on it? if so what did they try to do ?

You should check fuel level in jets. And check the pistons drop freely with a clunk ( damper removed).

It very mcuh doubt tis the needle.

The garage msut have messed with the sparks to see the va capsule was wet. So check points gap and static timing. To give 17mpg the sparks would have to be badly out....

Check the airway from filter housing to the underside of the pisotn is nto blocked by gasket - see page 13 and 12 of talk

https://supertrarged.files.wordpress.com/2017/07/final-pdf-how-does-an-su-carburettor-work-iwe-2017.pdf

That can easily give 17mpg ! maybe garage fitted new gasket set and did mot knwo to puncture those holes......????

 

 

Peter

Edited June 17, 2018 by Peter Cobbold

[Richardtr3a]

Thanks for the advice. I will check out the air filter this morning and maybe I need a rolling road. I am very tempted to try the weak needle SL in the Burlen book.

 

Thanks Richard

[anotheralan]

Since you have a non-standard cam and carb set up I recommend you take the car to a rolling road, preferably somebody with lots of experience with SUs. They will set up the mixture across the rev range and the timing to go with it. It is worth every penny to have a car producing lots of torque with no hesitation and good fuel economy. I took mine to http://www.mg-cars.org.uk/peterburgess/indexstart.html. Yes, he is an MG man but he tunes TRs and anything with SUs. I know he is too far away from you but it gives you a clue as to the type of person you need.

 

Mick

On the other hand, I do like the Peak District

Alan

[monty]

I tend to agree with Ian C, take it around the corner to Revington & get it sorted with TR people.

[Richardtr3a]

Hi Richard ~

 

Here's the vapour/fuel trap as fitted to my 3A. Make sure the trap is fitted pointing upward towards the distributor

as near vertical as possible.

 

Tom.DSCF1740 - Copy.JPG

I have just bought one 1H919 in the Moss catalogue. Does it matter which way up and how near it is to the carbs. It comes with a hanging bracket but I cannot see any suitable stud to use.. It will take some alteration as each end has a tight bend. Thanks for the picture. Week end in the garage with luck.

[anotheralan]

Good news. I have succedded in getting a result with the mixture. No more sooty plugs and without the need for a rolling road. Result!

I worked through the system checking everything. Replaced the points which were in need but not the problem. The only other thing changed was the piston springs which I replaced as the old ones were only 3oz. New ones 4.5oz. Invested in a litre of 20W for the dampers which has worked fine. Carbs were still in perfect balance when I restarted the car with Jets 12 flats down. Colortune on no1 and no4 weakening mixture equally in tandem. Final test with gas analyser 2 -2.5% CO through range to 3000rpm. Nicely tanned plugs after a run out but some popping on overun deceleration so i tweaked the jet down a flat

I have never been able to tune at idle without getting a rich mixture before now. I can only put it down to the springs as that is all i changed.

Runs and pulls really well but then it always has. No doubt I should get better consumption though.

No doubt a rolling road could refine the needle profile but i will review the value of that decision when i have monitored over a period.

Thanks for all your contributions and support

Alan

[Tonyloz]

So what needles dis you end up with?