Please help - Do I have the correct carb fitted???

[Dean]

Sorry about this, but I wish to know if I have the right carb on my car:

The tag says AUD 13
SU website says this is for a 1098cc.



My car is a recon 948cc Goldseal, I haven't a clue what year this was fitted.
My car is running a bit rich even when set to the weakest setting.

The reason I am asking is.. with a few bits and bobs can I get this carb to work correctly on my car. Or will I be wasting my money and be better off getting a different carb for my car.

You see the SU website lists numerous other HS2 1"1/4 carbs for the 948cc, so as you can see I'm finding it a bit of a technical overload...!

[bmcecosse]

The later carbs are much better - so yes - it will work ok. You may need to change the needle - but first make sure the fuel level is not set too high.

[Dean]

As simple as that... brilliant, cheers. When you say fuel set too high are you talking about the float in the float chamber allowing the chamber to overfill?

[bmcecosse]

Possibly - check by removing the 'bell' (two screws) and lift out the piston with needle attached. Switch on ignition and observe the fuel level in the jet - it should be about 1/4" below the top of the jet. If not - adjust the float. Look at the jet - is the little hole round - or does it look worn oval ? If so - new jet would be ideal. And - take the needle out of the carb - and report back the ID markings on the shank.

[Dean]

Thank you, with a capital "T"

[mike.perry]

Looking up my needle charts again, the correct needle for an HS2 carb on a 948 M1000 is an "M". If the carb is fitted with an AN needle it would previously been used on a 1098.
If the engine is running rich on it's weakest setting I would suggest that either the needle or jet (or both) is worn since there is very little difference between most needles at the tickover setting.
Check also that the needle shoulder is flush with the bottom of the piston and also check for wear in the butterfly spindle.

[Dean]

Just updating and yes Mike, after speaking with SU, I ordered an 'M' needle... fitted it and it runs great now.

AUD13 carb on a 948cc = M needle.

[Alec]

Hello all,

a general comment on S.U. problems.
Commonly it is advised that the jet or needle may be worn. How can this be a common fault as there is no mechanical contact between the two components and I doubt that fuel passing through will cause it? Certainly an off centre jet will cause contact but the car isn't going to run well enough to run for long like that.

Alec

[mike.perry]

Apparently petrol is abrasive.

[Alec]

Hello Mike,

but how abrasive? I still don't believe that worn jets\needles is common. My Triumph has Lucas mechanical fuel injection with very fine clearances in the metering unit and I have never heard of anyone saying that it has worn out due to abrasion from the fuel? (The fuel is also a lubricant for the M.U.)

Alec

[bmcecosse]

No! the fuel is not 'abrasive' or 'errosive' - any jet wear would be caused by contact with needle. This does happen in the later swing needle carbs - the needle is in constant contact with the edge of the jet.[frame][/frame]

You can see here - that the M needle is actually considerably RICHER than the AN needle !

[Alec]

Hello BMCE,

"This does happen in the later swing needle carbs - the needle is in constant contact with the edge of the jet."

True but I'd forgotten about that because it's too new for our cars. Why did they go to that design, it seems rather odd?

Alec

[bmcecosse]

To save having to 'centre the jet'' - it gives a consistent effect without any fancy setting up. Downside is - over the years - the jet goes a bit oval. And - on the HIF carbs - when you adjust the idling mixture - it is just that - it has no effect on the running mix. Older style carbs - the idling adjustment effects (only v slightly!) the whole running range, because it moves the jet up/down. The HIF has a separate idling circuit and doesn't move the jet.

[Alec]

Hello BMCE,

thank you for that, I have no experience of the later S.U. carburettors.

It does seem that as S.U. developed their products that they created more potential problems, such as the waxstat and the over run valve in the throttle plate. By having a separate idling circuit gets away from the basic simplicity of the original design. I suppose the ever stringent emission regulations had a large part in these complications?

Alec

[bmcecosse]

Both waxstat and throttle valve are emissions driven - for the US markets at the time. My TR7 has both - and surprisingly they are ok and it has so far passed it's MOT emissions tests ok! Although It still has the older jet adjust for mixture - and it is set nice and weak for the test!