SU HD8 needle recommendation

Saloons
1

I’m in process of rebuilding a pair of HD8 carbs to use on my 3.8 liter Mk2. The carbs were off a different size engine so I have no reference for which needle to run. Engine is in process of being rebuilt and will have larger intake valves, slightly higher lift cams and I plan on running pancake type filters. Car is manual with OD and I live at sea level. Hoping someone else has gone down a similar path and has a reference needle to start with. I don’t expect to get the needle 100% correct as I get the car running… but something close would be an excellent starting point. Any advice from the forum?

2

I think the general consensus is UM or UO. That would be a good place to start, and for the price of needles, I would just get a pair of each.

3

Greetings All,

Tapped, there are about 300 different needles for your SU’s.

Are you running the original air cleaner assembly, etc?

There are far too many parameters here to write a brief answer.

Moss Motors site has a primer you should read on “fine tuning SU’s”.
There was a better one but can’t find the link.

I exclusively run triples on mostly Jaguars. I have a set of exhaust manifolds with six ports welded that allow me to fit an O2 sensor to measure each cylinder.

While you don’t need to go that far, might be worth mounting two ports, that can be plugged once testing is done. That will allow you to see how each set of three cylinders are for each carb.

The bad news, make sure your tuning specs, regarding valve clearances are correct, and your distributor is up to snuff.

4

Thanks, Andrew and Lovell. Looking for a starting point and Andrew’s advice may get me needles that are in the ballpark. I realize there are hundreds of needles and hundreds of variables and would like to be able to get as sophisticated as O2 sensors eventually to pinpoint the perfect needles. Something workable in the meantime will get me out of the garage and I can adjust from there. I’m fully expecting this is not a ‘one and done’ exercise (like most everything else with these cars :slight_smile: ).

Tom

5

Tom how did this work out in the end, Its always nice to have a conclusion.

6

I would go to the Burlen website and use the needles from a 420 saloon as a starting point.

7

Hasn’t ended yet. Engine is still with my rebuilder. Might be some time before the car is back on the road. Based on input received though I think I’ll be starting with UM needles.