HS2 carbs

[CliveChafer]

Does it matter which AUD number HS2 1.25" carb I use I use on a 1098cc Minor? My dashpot is sticking horribly and I can't seem to make it run smoothly up and down in its channel. I can get a AUD359 off eBay for £40. Is there any reason I can't use it? I just rebuilt my old one, so I have all the rebuild parts I can put on the new one (including an AN needle) if they are needed (although it looks very clean in the eBay picture).

[philthehill]

Unfortunately it does matter which carb you do use.
You should select a carb from the link below and which is cross referenced to your vehicle.

http://sucarb.co.uk/cf/vehicle/list/?ma ... icle=Minor

Have you tried centralizing the jet in the carb body?
See the technical section of the above link for centralising details.

If you could please post a link to the 'e' bay item it would be of benefit.

If it is this item or similar http://www.ebay.co.uk/itm/SU-CARB-CARBU ... Sw0xRZmIiG
Whilst it will fit the float chamber will be at the wrong angle so not suitable for a Minor as is.

[CliveChafer]

Thanks, Phil. I thought centering was only necessary for the spring-loaded needles. I see SU give a procedure for fixed also. I rebuilt the carb a couple of months ago, but did not pay attention to this. Looks like the carb's coming out again!

So I really can't use even an earlier SU carb for a Minor (eg AUC924 or 944) if I replace the needle and jet? If the centering doesn't do the trick and let the piston move freely (I'm afraid it might not because there is some damage to the keyway on the side of the piston), a recon carb is about £150! Money I'd rather not spend. Let's hope the centering cures it.

Thanks for your help on this.

Clive

[philthehill]

You should really use the correct carb for the engine/car/year.
You could use the 924 or 944 as they have the float chamber at the right angle but you may have to change the needle and the dash pot spring.
Without looking at the fine detail they may have the engine breather pipe on the rear side of the body which if not going to be used can be blocked.
Centralising the jet is most important. Give it a try and see how you get on.
The piston (when the jet is centralised) should fall and hit the bottom with a nice clunk.
The anti rotational groove can always be fettled if required to give a clean rise and fall.
Phil

[CliveChafer]

Progress has ben made, and then not! I centred the needle in the jet, which took some doing. Every time I tightened the locking nut, the piston got hung up and wouldn't fall cleanly. I eventually manage to get it to work properly, by not tightening the locking nut too vigorously. I put it back in and it ran like a charm. I then adjusted the mixture using a Colortune and all seemed to be fine, until...

It suddenly started to misfire and stall. I checked the piston by putting my finger through the inlet, and sure enough, it was stuck at the bottom again. I took the piston cover and damper out, cleaned the inside, cleaned EVERYTHING, oiled the outside of the damper tube... and it ran ok again. But the idle still wasn't stable. There was misfiring, and I couldn't get the Colortune to give me a consistent reading as to whether it was running weak or rich. Then I found if I grabbed the bottom of the needle housing (the black plastic bit at the base), I could move it quite easily back and forth, and every time I did so, the engine started misfiring and running rough. Not surprising, since I was altering the position of the jet around the needle and making the fuel flow uneven. (There was more play when it was set rich, because there was more room around the needle; but even screwed in further I could still waggle it a bit.) I can't "set" the jet in one place. If I try to find the best spot for it, it quickly moves again, and the ragged firing starts again. Surely the needle should fit snugly in the adjusting nut and not allow any free play? Otherwise centring the needle is useless! Is this a sign that the housing is so worn that it doesn't hold the needle any more? I recently rebuilt the carb, so it has a new needle, jet, etc. I'm at a loss as to what to do next.

[philthehill]

The needle is secured in the bottom of the damper piston with the step/shoulder level with the bottom of the damper piston.
If the screw securing the needle is tight the needle cannot move or be displaced.
Once centralised the jet should not move other than when the choke pulls the jet down to allow more fuel into the engine for starting.
Once centralised screw the mixture screw right up and then unscrew 4 flats. This is only the beginning and can be used as a datum point.
Start the engine and screw the mixture screw down until the engine runs smoothly and when the piston is lifted slightly with say a small screw driver the engine speeds up and then dies down.
I personally would not put too much faith in the Colour Tune but look at the colour of the plugs after a run. If the mixture is correct they should be biscuit brown. If they are lighter richen the mixture, if they are dark weaken the mixture. Road testing is the best way to set the mixture.
Make sure all the other items that enable the engine to run are working or correctly set i.e. ignition.
Phil

[CliveChafer]

The problem is not with centring the needle anymore. As I said, I finally managed to get it centred ok. But as soon as I adjusted the mixture, the engine started running rough again, and when I hold the bottom of the jet housing (the black plastic bit), the jet moves around quite easily. So the needle cannot stay centred and the fuel flow is uneven. I'm trying to figure out if there is a reason for this looseness, and if I need to buy a new carb body to get the needle and jet to stay where they are put.

[philthehill]

The body of the carb does not have any bearing on the centering of the jet.
The centring of the needle is fixed by the damper and damper dashpot and therefore cannot be adjusted radially only adjusted vertically relative to the bottom of the dash pot piston.
It is the centering of the jet that you should be concentrating on.
The jet has a lever attached to it which connects with the choke linkage whilst the jet can move up and down the jet is not supposed to rotate or move radially in the jet holder.
There has to be something missing from the jet holder for it to move excessively as you describe.
Read this link and you should be able to determine if all the parts are there.
http://sucarb.co.uk/technical-hs-type-c ... djustments
Page 2 para 3 refers.
Can you please post a picture of the underside of the carb.

[mowogg]

Looking through this are you sure thr needle is centred. I would worry when you say you did not tighten it up when centering the jet and you can still move it

I have found IT very helpful to disconnect the choke mechanism while doing this.This normally allows easy centering and enabling into tighten down.

The other issues I have had is worn needles and jets. I always replace if I do not know the history as it saves you time in the long run.

[philthehill]

The needle as I stated above cannot be centred as it datum is fixed - only the jet can be centered relative to the needle.
If you think that the needle is bent and to determine if the needle is bent or not roll it on a piece of glass and if bent will easily show up.
As regards worn needles - the SU is very forgiving as regards wear to the needle. The main area of concern as regards wear is the throttle spindle holes which if worn excessively can draw air in past the throttle spindle but the SU will normally go some way to compensate for the extra air.
If you follow the instruction in the link http://sucarb.co.uk/technical-hs-type-c ... djustments to the letter and there are no missing or damaged parts the carb can be easily set up.

[CliveChafer]

I'm pretty sure I understand how the SU carb works, and how the needle and jet interact. After I had successfully centred the needle in the jet and consistently got that satisfying metallic click when the piston was dropped – and this was happening both before and after I installed the carb on the car – the engine ran quite smoothly. I then followed the usual procedure by richening up the mixture (until the Colortune turned yellow/orange) and then gradually weakening it to get the fastest and smoothest idle. But instead of running better, it started to misfire and idled very roughly. I realised that I could affect how it idled by moving the base of the jet (the black plastic bit) laterally. As you would expect, since I was effectively changing the relationship between the jet and needle, the roughness of the idle changed significantly as I moved the jet from side to side, which it was quite easy to do. So I could not keep the perfect centering of the needle in the jet that I had achieved before reinstalling the carb.

I can see the jet moving at the base of the carb as I apply a light sideways pressure on it. The locking nut does not move against the base of the carb, only the jet and spring. I have looked at the diagrams of the carb, because I too thought there might be something missing that would keep it firmly in place, but the carb is complete. The only thing I can think is that the hole that the jet passes through in the locking nut has somehow become enlarged, and this now allows too much free play between the jet and the nut. I realise there has to be a fractional amount of movement there to allow for centering the needle in the jet, but I assume once the locking nut is tightened in the right place, the possibility of lateral movement should be completely eliminated. So the question is: am I missing something? If not, the only thing I can think to do is to buy a new carburetter body and see if I can get the needle to stay put in it.

[philthehill]

You have not mentioned the jet tube that the jet sits inside.
It is not itemised in the SU diagram link above.
If the jet tube is missing the jet is able to move radially around the needle more than it should.
The jet tube is shown in the SU diagram but you have to look closely to see it.

The parts you should have are:
The jet.
The jet tube.
The locking screw/nut.
The spring
The jet adjusting nut.

Buying a new body will not alleviate the problem.
Para 3 in the attached link shows an explodes view of the jet assy,
http://sucarb.co.uk/technical-hs-type-c ... ismantling
Items listed as 12 & 13 should be fitted to your carbs.

[Sweeny]

I hope this helps and I'll throw in my 2 cents, it was recommended to me to polish the inside of the Piston Unit to give a really smooth operation when the piston moves inside its housing. After doing this I found it made a surprising difference. What grade of oil are you using in your oil well?
Cheers,
Tom

[philthehill]

A photograph of the jet assy disassembled and the underside of the carb in the area of the jet holder would be of great benefit.

[CliveChafer]

The jet tube is present. Here are a couple of photos of the underside of the carb, although I'm not sure what they reveal.

P1030738.jpg (10.13 KiB) Viewed 4753 times

P1030736.jpg (10.73 KiB) Viewed 4753 times

[philthehill]

Thank you for the pictures. I did ask for the disassembled jet assy to be photographed as that would tell me what is there or is not there and most likely give me a pointer as to what the problem is.
See post below:-

[philthehill]

I have blown your picture right up and I think I have found the problem.
The jet adjusting nut is upside down.
Being upside-down it will not therefore hold/secure the jet tube so allowing the jet tube to float
http://sucarb.co.uk/technical-hs-type-c ... ismantling
See the link above for the correct orientation of item No 12.

[CliveChafer]

Wow! You have very good eyesight!! I will turn it round and let you know what happens.

[philthehill]

It does help when you are able to enlarge the picture.
It does make me wonder that if the jet adjusting nut is the wrong way round what else is not assembled correctly.

[CliveChafer]

Well, all was not what it seemed. When I got the carb off the car, the adjusting nut was the right way round. I think the shiny metal at the top of the jet base might have looked like the top of the adjusting nut. In any case, that wasn't the cause of the lateral movement in the jet. I took some pictures when I had the jet etc. disassembled. I think you'll see there is nothing amiss with the carb. I reassembled everything again, and the piston stuck firmly at the bottom of its travel. I recentred the jet and it was good - until I reattached the arm for the choke. Even that little bit of lateral pressure was enough to make it bind again. I slackened the lock nut slightly and recentred it with the choke arms car and I may not be bosom buddies...

P1030755.jpg (228.63 KiB) Viewed 4671 times