SU Hs6 Carbs on a GT6

[Upriis]

??)I am after a little bit of help / advice. ??)
I have brand new HS6 carbs fitted using Triumphtune adaptor plates on a standard GT6 Inlet manifold, these are fitted to a 2.5l TR6 Engine.
The problem is the  fuel level on the rear carb is far lower than the front. (this is plainly evident when looking down upon the top of the jets)
the only reason i can find for this to happen is because of the angle of the engine instalation.
I have tried using spacers under the float valves and increasing the length of the float needles to make the fuel levels different in the front & rear float bowls / carb jets, but there is not adjustment to make them level >:(
I have a wideband air/fuel meter that i can connect to both collectors on my 6-2-1 manifold.
on the front carb to get a fuel ratio of 13:1 at idle I nedd to lower the jet from flush 11 flats while the rear carb nedds to be turned down 20 flats.
this obviously makes both carbs operate on a different part of the metering needle throughout the entire rev range or am I reading too much into this? :-/ ??
anyway any help would be greatly apprieciated. (before I have to look into dellortos ;D or electronic fuel injection ;D ;D)

[James]

Check your float levels etc - and adjust accordingly - that is what allows you to adjust fuel level in the bowls.

[JonB67]

Can't be down to the level of installation. The fuel level in the bowl is directly regulated by the float and jet - its entirely independent of the other carb. Shouldn't matter if the difference in height is 1/8th or a foot! (assuming both are upright enough to operate correctly)

Like james says... check the float height.

Jon

[Upriis]

I have adjusted them to the max (lowered the front float by adding spacers under the valve and elongating the needle in the valve)
Thanks for the suggestion though james :)

[12 point 75 to 1]

On a slightly different tack have you tried letting your front tyres down alittle!!!!!

Sorry could resist - there's always one!!!!

[Upriis]

Didnt think of that one but the wife did suggest tractor wheels on the rear ;D

[Upriis]

hopefully the following basic picture might explain my problem better than i can explain it :B

It appears that the fuel level is lower on the bottom left float bowl but it is just an optical illusion (that or sunday drinking :o)

[Deleted User]

upriis sorry but i have no idea how to solve your problem, but im just wondering if thats the car i think it is? BAM something? met blue with recaro seats etc?

[Upriis]

yes jony I have spoken with you before.
How is life with the yellow one?

[Deleted User]

its gd mate! good to see you on here. i thought for a min there that your custom engine bay SS plate things (too early in the morning to think hhaha) had gone global ;) and i also now know what you mean by saying having the triumph logo put in the seats costs almost as much as the seats themselves! lol

[JonB67]

So presumably the options are; make spacers to correct angle of installation, which then gives problems with throttle actuation or do what steve downing did and instal a spacer on the rear and deck the front bowl a little:

http://members.boardhost.com/GT6-Spitfire/msg/1174009303.html

or do as nick jones suggested and run a pair of HIF's... which would probably be the best solution, and maybe the easiest too.

Jon

[99176]

To get that much disparity I would have thought it would look more obvious in the picture.
I dont think the adaptors would both be drilled wrong to give the slanted effect, besides the linkage would tighten up.
I can only suggest going back to basics, are the needles

[99176]

Sorry got cut off;
Are the needles straight and do both dashpots drop firmly onto the bridge?

[a turner carbs]

Hi, check which float chamber you have fitted ( there is a number cast near the connecting boss ). The one nearest the radiator should read AUD2140 and the one nearest the bulkhead AUC1310. If you have these fitted it will solve your problem. 

[willcolumbine]

I wouldn't have thought being at a slight angle like that would make any meaningful difference to anything. Sidedraught SU carbs are old, old, old school technology and as long as they're not vertical or upside down they should be fine. Surely if it made that much difference we'd all have problems when we braked or accelerated and the petrol sloshed forwards or backwards?

Also the needle will always provide the same restriction in the jet whatever the height of fuel. If both needles are filling 50% of the area of the jets then the fuel height dosent matter. Fuel is drawn into the carb by capilliary action and it is the restriction of the needle in the jet that provides the metering of fuel. So at any slight angle it wont make a bit of difference.

If I were you I'd be checking out other aspects of the carbs!

[a turner carbs]

Will is right and the car will run but if you want it to run correctly try following my advice. Triumph recognised this problem and so did Stromberg. The Stromberg carb has been approved for use on light aircraft because of it's ability to provide correct fueling despite being inclined. This is also the reason why Land Rovers use the Stromberg or the horizontal integral float chamber ( concentric jet ) SU carb.

[Deleted User]

I knew it! No one listened!

The stromb IS better than those poxy SUs!

[99176]

When I want to loop the loop I will convert straight back to Strombs.

[Deleted User]

SU's for MG's, Stroms for Triumphs. Triumph took a 30 year old design from SU and made it better with the Stromberg. 1961 wasn't it Andrew with the TR4 when Austin Morris were holding ST to ransom over SU deliveries?
Having to work on the things day to day certainly makes me prefer the Stromberg for it's longevity, and abilty to hold a tune longer than a SU. I see SU's wearing out every 30,000 miles, yet Strombergs rairly need major work until they have gone over 100,000.

[Upriis]

Many Thanks for all the replies.
The above basic picture is obviously exaggerated, however the principle remains. The metering needle is not the same difference in thickness throughout its length The needle i am using presently is BCH  990, 950, 920, 892, 863, 833, 800, 772, 745, 722, 700, 678, 656, 634, 612, 592 so theoretically if fuel is being delivered from mettering point 6 on the front carb (863) and point 9 (745) on the rear carb on lifting the throttle to the next metering point the difference in fueling will be 30 on the front carb and only 23 on the rear carb. (again i may be well out of my league with this!)
the car has always run very well and has a lot of power. I am trying to seek the best as possible from this engine (the problem has only been found after using a wideband air/fuel ratio monitor)

I have attached a simple spreadsheet that I have used to try and make sense of this confusing subject (it may be of use to someone)

[Upriis]

Quoted from JonB67 do what steve downing did and instal a spacer on the rear and deck the front bowl a little:

http://members.boardhost.com/GT6-Spitfire/msg/1174009303.html

Many Thanks for that link it explains my problem precisely

so solutions so far
machine the HS6 float bowls
Obtain AUD2140 & AUD1310 float bowls
Obtain HIF 6 carbs (can HS6 needles be used? dashpot height issues?)
Obtain stromberg 175 carbs (aren`t they more difficault to tune with less parts available and less metering needles available)
Obtain webers/dellortos + manifold+ linkage+etc etc
find a way of fitting fuel injection mechanical / electronic

[Upriis]

Quoted from a_turner_carbs Hi, check which float chamber you have fitted ( there is a number cast near the connecting boss ). The one nearest the radiator should read AUD2140 and the one nearest the bulkhead AUC1310. If you have these fitted it will solve your problem. 

;DMany thanks ;D
have checked the numbers and I have AUC1310 on the front and rear float bowls.
I have also just checked one of my spitfires which has number AUC2140 on both the front and rear.
am I correct in thinking I can change the bowl over :D and get a new 2140 bowl for the spitfire as and when?
I have not measured the bowls but I presume the 2140 is taller ??)???

[Upriis]

I have swapped over the float bowls and shimmed the valves as appropriate. The adjustments on the main jets are now 12.5 flats down for the front carb and 14 for the rear one to give a reading of 13.5 A/F ratio on each (close eneough for me ::)).
many thanks for all the help and suggestions ( ;D particularly a turner carbs ;D)
I have attached a photo of the float bowls to highlight the difference and help any others who may have the same problem (1310 on the left 2140 right)

Anyone on here know of anyone that can gas flow inlet manifolds and aluminum weld? I would like to replace the adaptor plates so that the carbs will fit directly to the manifold. (i understand that the TR6 / T2500 tc dont fit under the GT6 Bonnett)

Once again Many Thanks (due to the help freely given on here I have become a fully paid up member of Club Triumph 8))

[Clive]

I have one a simple conversion. I tapped the existing holes in the manifold to 12mm and cut a thread on some 12mm ali rod. Wound it in/cut and filed flat. Then just redrilled new holes and tapped for the HS6 carbs. Much neater than the adapters.
As for gas flowing, I scribed a mark inside the carb gaskets, and used a "cone drill" to grind the manifold out and get rid of the step. I never bothered polishing any further, or attempting any other flowing.

I know Chris Witor has worked on saloon manifolds, but I do not know if he has any knowledge of "our" manifolds. He is honest about these things if you ask him!

Clive

[Upriis]

I shall try Chris Witor. I really want to mount these up on all 4 studs.
does anyone know if gasflowing the inlet manifold has major benefits to performance or am I better off looking for performance gains with different type of carbs.
for info the engine is 2.5 st3 unleaded, fast road 89 cam, roller rockers, etc