The Triumph Dolomite Club - Discussion Forum

Hi Group,

Does someone know what type of needles are used in the Sprint carburettor. Rimmers catalogue gives CUD 1141, CUD 1159 and NZX8015. I suppose that CUD1141 is BBT but what are the others? My '76 Sprint engine vibrates by slight acceleration or gently opening the throttle and hesitates to accelerate. By full opening it runs perfectly.
I suppose it could have something to do with fuel mixture.
Any ideas...

Thanks for all suggestion, Eric

Eric wrote:Hi Group,

Does someone know what type of needles are used in the Sprint carburettor. Rimmers catalogue gives CUD 1141, CUD 1159 and NZX8015. I suppose that CUD1141 is BBT but what are the others? My '76 Sprint engine vibrates by slight acceleration or gently opening the throttle and hesitates to accelerate. By full opening it runs perfectly.
I suppose it could have something to do with fuel mixture.
Any ideas...

Thanks for all suggestion, Eric

It's most likely to be the ignition system IMO. Make sure the bits and bobs in there are all in good nick first.

Eric wrote:Hi Group,

Does someone know what type of needles are used in the Sprint carburettor. Rimmers catalogue gives CUD 1141, CUD 1159 and NZX8015. I suppose that CUD1141 is BBT but what are the others? My '76 Sprint engine vibrates by slight acceleration or gently opening the throttle and hesitates to accelerate. By full opening it runs perfectly.
I suppose it could have something to do with fuel mixture.
Any ideas...

Thanks for all suggestion, Eric

On the carburettor float chambers there shold be little tags to identify which carbs you have.
The codes are for different years of manufacture
1973/4 AUD545........needle CUD1141 (BBT)
1975/6 AUD680........needleCUD1159(BCM)
1976 AUD663.........needle NZX8015 (BDQ)
1976on FZX1257........needle NZX8015 (BDQ)
This information I have obtained from the SU Catalogue.
If there are no tags fitted Eric, then you could post a photograph of the carbs showing their jets, and we should be able to determine which type you have.

As Dave has already said, start with the ignition system.
The rotor arm to distributor connection, through the spring loaded centre contact, is a weak point that gave me bother in the past.

I've just recently wheeled my Sprint out of the shed after 18 months and it ran as rough as guts. Filled it up with nice new BP Ultimate petrol (98RON) and took it for a good half hour run - still terrible. I was tempted to start with the carbys as I know that they were out when I stored it, but resisted by repeating over and over to myself the old saying '...95% of SU carby problems are in the electrics' Especially when you're dealing with Lucas - The Prince of Darkness.

Went right through ignition sysem...Sure enough, faulty main lead from dizzy to coil, plus points gap had closed up....running much better now but still not right, so new set of spark plugs....even better still, but then it actually had similar symptoms to yours. Decided to change the coil, not sure of my reasoning but I know that its well over 10 years old and I'm on a roll with the ignition sysem, getting improvements every time I adjust or replace something. In goes a new shiny red Bosch GT40R.

Problem disappears immediately!

Why - who knows? It should give trouble at high revs or under heavy load, not mild acceleration. Yes, my carbys are still to be adjusted and will make a substantial difference, but I'd definitely do as the others say and check the usual suspects in the ignition system first.

David

Hi Group,

Thanks for Help. I had BBT needles in my AUD680 carburettor I changed to BCM. On the electric side, I have an electronic ignition (retaining my points) and a Super Gold ignition coil. I already use NGK Iridium spark plugs which improved idle a lot. I hope that the needle change will improve things...

Eric

Eric wrote: My '76 Sprint engine vibrates by slight acceleration or gently opening the throttle and hesitates to accelerate.

As the throttle is opened the carburrettor pistons rise. If they rise quickly they are inclined to travel a little too far, this will then weaken the mixture briefly until pistons get back in sync with the throttle, hence the hesitation before accelerating.
To slow the pistons, oil is used in the dashpots - make sure it is the correct grade.
There are springs fitted inside the carburrettors against the pistons - these may need replacing (Sprints use AUC1167 in all models).

Hi Ian,

Thanks for your explanations I replaced the springs some time ago and I use 20W50 Comma Oil. Should I try with gearbox oil?

Eric (I also legaly use a black number )

20w50 was originally specified for the dashpots, gearbox oil will be too thick I would imagine. You can also buy SU damper oil from various places though it's probably quite expensive for what it is.

Use light machine oil or ATF. That's all I've ever used, been instructed to use, and have had no issues with it in several engines.

May as well use 3 in 1, thats what i used in my SE many moons ago based on what an ex canley chap told me, worked fine

Eric wrote:Hi Ian,

Thanks for your explanations I replaced the springs some time ago and I use 20W50 Comma Oil. Should I try with gearbox oil?

Eric (I also legaly use a black number )

Hi Eric, I suggest you try gearbox oil as a comparison will be worthwhile. You could then let us know what difference you find.

Gear oil is pretty similar viscosity wise to 20w50.

I use whatever engine oil I have laying around, something around 10w40 or 20w50 should be fine, Using something really light will lessen the effect of the damper so the piston will shoot up and it'll go really lean when you stamp on the throttle.

Hi Eric,

If there's no ignition problems, then take of the airfilter(s) and get someone to rev the car while you watch the carby pistons. They should rise the same amount at the same time. If they don't, check that one of the damper rods isn't slightly bent and also that the pistons aren't rubbing at all on the sides of the suction chambers as they rise. Also if the suction chambers have been swapped and put back on the wrong carby you can get odd problems.

Interesting to see if heavier oil makes any difference. I use 20-50. The proper SU oil is 20 weight. Transission fluid is a bit lighter. I tried 70 weight once and didn't notice any difference, although it would have made it richer under initial acceleration.

David