Su Waxstat Hs4 Carbs

Let me start by saying that my Mini has dual HS2s and will keep them.

However, I just bought a used HS4 Waxstat carb off eBay. My intention is not to build it for the Mini, but use it (eventually) on our project Spitfire as it has a 1296cc engine in it.

I don't want to leave the Waxstat in place. I understand a method of converting the carb is to disassemble the jet tube, remove the thermostat, and re-assemble it with two pence coins inserted in place of the thermostat. Since pence coins aren't common over here... would one of you put some calipers on a pence coin and tell me how thick they are and what diameter they are? Thanks.

I'll be looking up the common needles and springs used with HS4s when they were used on Minis. However, if any of you can tell me what color springs and which needles were used on 1275 Minis I'd appreciate it.

Thanks in advance.

19mm in diametre and 1.27mm thick.

25.95mm by 2mm

Red spring 90thou jet
AAV 3.5 to 4.5% CO
ABB 3.0 to 4.5%
AAT 3.0 to 4.0% all from 1275GT

AC is standard, BQ rich, HA weak on early fixed needle carbs


Seeing Mike's reply did you mean 2p or 1p coins? the 1p coin in front of me is 1.5mm by 20.28

Thank you both.

I meant two 1-pence coins. It looks like I need to plan on something a little over 19mm diameter and close to 3mm thick. I don't think it's critical as the parts are crimped back together and this will allow some tolerance. The coins just fill the gap where the removed thermostat once sat.

Ethel, thanks for the jet and needle info. I looked in my SU book and while the spring and jet seem to be standard across the board, a plethora of different needles are recommended. Within the BMC 1275 engines... there were at least 4 possible "standard" needles for various cars. Then I checked the 1296cc Triumphs. Not one needle was specified the same as those on the A-series and like the A-series, there were at least 6 different possibilities.

When I get the carb from the seller I will have to change needle and possibly the spring as he was running this carb on a 998 A-series. I'll have to research this further and ask on another board in the U.S. what people have done when they've replaced their Stromberg like I'm planning on doing.

I really don't have a problem with Strombergs. Our GT6 has them and I don't find them any harder to work on than dual SUs. However, the Spitfire has a single emissions type Stromberg that requires needle adjustments using a special tool reaching down through the carb's dashpot. I'm not comfortable with that yet... and may never be.

Thanks again.

Edited by dklawson, 01 December 2008 - 01:24 AM.

Update and follow up.

The eBay carb and parts carbs arrived today. Apart from the pleasant surprise that they got here so fast... I was delighted to find that the parts carbs vacuum pistons had needles installed. One was bent and had to be straightened by careful tweaking in my lathe. The other needle was reasonably straight. One needle is an "ADD" and the other an "AAC".

The ADD turns out to be a lean needle and the AAC a rich needle. The AAC was apparently used with some inline 1275 A-series applications. It looks like all I may need to do to use the complete carb is swap needles and reposition the float bowl for the Triumph's horizontal manifold.

Christmas may have come early for me!

Thanks again all.

What did you end up using in place of the 1-pence coins as I live in the US as well.

I haven't worked more on the waxstat yet. (I'm still on Christmas vacation... so maybe this week).

Just before Christmas I bought another pair of HS4 carbs in addition to the carbs (and related parts carbs) which prompted this thread. One of my project cars is a '72 Spitfire. A local guy was desparately trying to get rid of a parts car and get Christmas money. He sold me a complete HS4 setup for a 1500 Spitfire (manifold, linkages, carbs...) I've been working on that set of carbs as they have traditional solid jets. That said, I still plan to fix up the single HS4 waxstat and change it's needle for use on the Spitfire. (The duals will go on once my sons leave home and no longer drive the car).

Basically all you need is something that will fit inside the jet assembly in place of the wax thermostat. This could be ANYTHING close to 3/4" diameter and about 1/8" thick. Coincidentaly, our penny appears to be about the same size as a 1 pence coin (3/4" OD x 0.06" thick). So my first attempt will be to use 2 pennies.

The last post inspired me so I worked on my HS4 carb today. I have documented in a brief PDF what I did to convert the waxstat jet to a fixed jet. Those interested can read over the procedure at:
http://home.mindspri..._Conversion.pdf

I've got a spare carb in the garage so thought I'd give this conversion ago.

Think I've spotted why the original conversion Doug links to only used 2 x 1p coins. They also used the steel button out of the waxstat unit. That button plus the 2 coins would be enough to put the jet back in the original position.



But just how does the unit work ?? I was expecting the steel button to move, but there is nothing under it except a hole. So does the whole of the copper section expand ??

I think you have a great explanation for why my conversion went differently. I didn't see that metal pin as a separate part from my Waxstat... it was stuck in the copper part. Good catch.

I haven't tried any experiments with the copper cartridge. I assume the whole thing is filled with a "wax-like" fluid and that it expands when it heats up. The idea is that the length of the cartridge increases as it heats, lifting the jet tube against the spring in the housing. This would lean out the mixture as the engine compartment heats up.

I bought a Waxstat Conversion Kit for £12 approx. It was a full new jet to replace the entire WaxStat Jet assembly

Have a look at -

http://www.calverst....3d6e6127be8ac22

states -
This is to convert the Waxtstat type jet to non-waxstat type. Why do this? Because the Waxstat jet is great for mpg and road driving economy, but not great for best power. When the waxstat jet detects under bonnet temperature at a certain level, the jet is raised, leaning off the mixture. This is not at all good for best performance. So rather than have to change the choke linkage drop rod as well as the jet, this jet comes witha small bracket that connects to the origininal waxtstat choke linkage. Very useful for such as Class One Grasstrack racing. It will only fit the standard single SU as fitted to Minis - with the float bowl on the right side of the carb.

The jet I've converted looks new, so its only cost 2p to convert to a fixed jet

Edited by lrostoke, 21 January 2009 - 07:15 PM.

Very weird, wondering if there are different types of waxstat unit.

Today I removed my jet assy and replaced it with the modified jet assy. Then I stripped the old jet assy and noticed following

This one does seem to have a waxy substance that expands into the cavity. You can sort of see a grey jelly in the bottom



But the other assy I stripped doesn't , tried heating it on the stove no sign of any expansion of waxy substance.



The other thing I noted was this, the one on the left was on my car, the one on the right was on the spare carb,
left one did have waxy substance, right one nothing



But appart from that converted jet is working a treat, cars running fine.

Edited by lrostoke, 24 January 2009 - 06:58 PM.

just out of intrest, whats the benefit of converting to a fixed jet?

From what I've read waxstats main purpose is to reduce emmisions and improve mpg, it does this by weakening the mixture once the engine bay reaches a certain temperature. This can rob the engine of some power.
I converted mine because I'd been having trouble with it cutting out at junctions once the engine was nice and toasty, appart from junctions it was fine, so as a long shot I figured the mixture was weakening off when hot, causing low rev problems.
After I removed my original waxstat I did notice a dent in the bottom, I don't think that would be original so that could have been my problem that it was damaged. No idea how though had a look round the bulkhead and nothing there to cause a dent.

Edited by lrostoke, 24 January 2009 - 07:15 PM.