What kind of needles should I be running in my HS6 SU carbs? They had DX needles in them.

What's the difference between these and the recommended KB's?

thanks

I ended up putting DX needles back in (two new). Maybe I'll play around with a couple other ones at some point. The carbs are back in and purring and the car sounds great! I'm waiting until I get the car tuned up, new ignition stuff and spark plugs in, and timing adjusted before I declare victory but I sense the car is going to run A Lot better.

My new exhaust system is also on its way. :)

Hello Belinda,
There is an SU guru living in Sweden, that probably could sort out your problems, but it seemes that he has no homepage.
However, We (if we can, could get you in touch with him.)(of cause with no charge).
BrG, Dennis.

The springs should be the same in each carb. The sticky piston would have definitely caused you to have backfire issues on overrun. It isn't critical to have identical floats in each carb but it would eliminate one variable.

The DX needle is the higher performance needle. The KB was reccomended for the B18D version of the motor. The SM was recommended for the B18B version.

I have posted a graph of needle diameters on the photo gallery FYI.

Mike!

p.s. Chasing issues around on carbs will drive you crazy. Make certain you re-tune the entire engine after any alterations so you have good gaps, timing, lash, etc. I suggest getting a full rebuild kit (gaskets, throttle shafts, butterflies, jets, needle valve) and a replacement spring and two new needles. It is nearly certain that the needles in those carbs you have are worn and only "resemble" whatever they are marked at anyway.

--
Mike!

Unless you are accurately measuring horsepower, elapsed times and top speeds,
there is probably no detectable difference. Both were used in various models
of Volvos with B18 engines.
--
George Downs Bartlesville, Heart of the USA!

Gratzi. I have another question, maybe you can answer

When I pulled the carbs apart I noticed one of the floats is all plastic. The other is plastic except for a metal clip on the top. The p/n of this float is AUD9202, but I haven't been able to find it (and I even called the guy in NY, Joe, the SU guru)

I figured it was probably important to use the same kind of float in both carbs, to ensure the valve closes in each at the same fuel level. I tried to find the one with the metal clip, if for no other reason than it seemed more elegant design--the body of the float is exactly perpendicular to the valve when it closes the valve. The plastic one is cocked at about a 30 degree angle when it's closed.

Is there a difference?

When I asked Joe about that he was unaware of the all-plastic model.
I believe if both of the floats are good (no gasoline inside them, not
broken, etc) and if you set the float level correctly on both carbs it
should be OK.
I've used them both ways and they seem OK.
--
George Downs Bartlesville, Heart of the USA!

I think having the proper needles makes a big difference. It depends on what motor you have. B18? B20? Any known hot-rod stuff, or just a regular one of those? Which one (it's cast into the block on the left side)?

The plastic float with a metal tab on top is the standard one we see these days. I've had very good service and parts from Rhys Kent, who posts on this board often. (No affiliation, blah blah blah...)

www.sucarburetors.com

He could also recommend what needles would work well with your motor.

Burlen Fuel Systems in the UK supply only the all plastic float for all HS type carbs - they describe it in their catalogue as non-adjustable and say that it supercedes all previous HS floats. As George says though, the important thing is the float level in the bowl - once the floats achieve the correct level then there's no problem.

As far as the correct needles are concerned, if the car is not running lean or rich on the current needles then the current needles are probably ok.

Aidan
--
1967 131, 1969 131, 1973 Triumph GT6

I noticed another problem. The springs are not the same in the two carbs.

Joe Curto sold me the all plastic float. I think I did contact Island Automation. Can't remember if I asked them about DX vs KB needles.

What are the symptoms, exactly, of the carbs not being synchronized?

Bad synch results in noticeably rough running at small throttle openings. This refers to airflow through the carbs, though, not mixture imbalance.

Remove air filters, put your head down in the engine bay and listen to the carbs at idle. You can hear quite accurately if one is drawing more air than the other. Balance them out with the idle speed screws at the outboard top on each carb, maintaining a civil idle speed, until they both sound the same.

Then work the throttle gently by hand. You want to see the pistons on both carbs rise at the same instant. Adjust the cranks on the shaft that goes between the carbs so they do that (8mm nut driver is handy here).

Your best indicator of mixture is to examine the spark plugs. Look at the center procelain insulator -- electrode color has zero meaning, contrary to eons-old popular belief. If there's any soot on the insulator, you're running too rich for both best power and best economy. Richen until you get a little ring of soot at the base of the insulator, then lean until it just goes away.

If it doesn't look like that in all situations -- gets sooty at idle but look right after a freeway drive, for instance, or vice versa -- you have the wrong needles.

A stock B18 does well with ZH needles, and a stock B20 SM needles. KD and DX are more for high-performance motors, and will run rich on the highway in a mild motor if adjusted properly at idle.

Of course it does help to have the fuel level the same in both float bowls. Not saying you don't, but it's hard to have confidence in it if you have two styles of float that adjust differently.

Thanks Phil, I'll do that (look at the plugs after different driving conditions)

Exactly --the floats are different, and so are the dashpot springs. So it's hard to believe the carbs will be synched when there are differences between them (parts-wise)

Also, another problem that was obvious when we pulled them off was the dashpots "fell" at different rates. At first we were thinking about trying different weight oils in each to even them out (we ended up using 20W 2-cycle motorcycle engine fork oil in both). But that wasn't the problem. The problem was one of the dampers was bent. So instead of sticking straigt up, perpendicularlly, it was 2 or 3 degrees off. This caused one dashpot to take almost twice as long to fall as the other one. Once straightened out there was a big improvement in the rate at which they fell--they went from 5 seconds difference to ~1 second difference.

The car was backfiring a lot when in gear only when my foot was off the accelerator, in other words when slowing down. So I used to shift into neutral and coast to stops to avoid this. Do you think this was a symptom of carbs not balanced?

It's a B18.

Belinda, if the bent damper was causing a piston to hang in the up position, that would surely get you some raw gas lighting off in the exhaust. Be sure they drop cleanly after you push them all the way up by hand (and any oil that comes out the top vent when you do this is excess, BTW -- that's as much oil as they need).

20W oil is a reasonable choice. The heavier the oil, the more enrichment you get upon initially opening the throttle. This is what SUs do instead of having accelerator pumps.

Ideally the springs should be the same, of course, but it's not super-critical. You can try stretching the weaker one out a bit.

If you set the mixture for best idle (fastest, smoothest), DX needles will surely be quite rich at speed on a stock B18. I'd try ZH needles (this is off the top of my head, but I think those are stock for B18D).

I got two new springs (red), two new floats (all plastic) and the holes are being machined in the butterfly shafts. Overall, I think I'm coming out ahead because I've only spent ~$150 on misc parts (floats, needles, etc) and a kit which included new jets, float valves, shafts, butterflies. I decided against trying to press new bushings in there. If they wear out in a couple years, I'll machine them out, and press Teflon or steel bushings in then.

The carbs get reassembled tomorrow :)

The last rebuild kit I got from Burlen had the plastic/metal floats, go figger. The only replacement throttle shaft bushes from Burlen are the teflon coated steel so they should be the last bushes those carb bodies ever need as the shafts will wear long before the bushes do!

My biggest issue was getting that darned taper pin out of the throttle shaft and replacing it. I ended up drilling oversize and using a common sized roll-pin locally sourced. Try to get as small a gap between the bell-crank and the carb body without causing binding... Install the butterfly first before drilling the shaft!

I'm with ya, as I've always just redone my own.

--
Mike!