14 replies to this topic

[thebullet]

Hi guys, bit confused.

I am rebuilding a set of twin hs2 carbs. The plastic jets currently fitted look cheap, don't go into the float bowls properly and when I got them had sealent gunked all over them.

Now I have seen on many HS2 twins before the braided pipe with brass ends. Such as... http://bullmotifmini...rge/aud9098.jpg

Minispares don't sell these. Are their plastic ones any good? they sell ones for each ends of twin carbs, why is this?
Also, what jets would be suited to my car, 998, 12g295 head and Stage 1?

Thanks.

Edited by thebullet, 10 February 2012 - 10:11 PM.

[bmcecosse]

A large single HIF 38 will be best for your engine ........ You don't change 'jets' - you change the needles -what's in the carbs at the moment?

[thebullet]

Ah right, well I have a HS4 currently, flat spotted and just wanted a big more torque and as mine has the cooper head it will almost be the same spec as the coopers.

Oh I understand that, I just noticed they had different coloured bands on.

http://www.minisport...fo_AUD9141.html

This says it is for single but if i get 2 of them for my twins, will it work?

Not sure what they are, black, with a plastic nut on the end. Really cheap by the looks of it.

Edited by thebullet, 10 February 2012 - 10:22 PM.

[Dan]

Where have you found any jets with a plastic nut? The ones sold by both Mini Spares and Mini Sport are genuine AFAIK. They aren't braided, they have a steel spring protecting the Nylon fuel hose and a brass tube nut with sealing washers.

There are indeed different colour coded jets for SU HS carbs, and many small niggling problems with the setup of SU carbs are caused by people assuming that they don't need to change the jet (and other details) when moving a carb from another car or building a pair from singles. Jets (like carb bodies) are handed, so no you can't just use two Mini single carb jets. The tube connects to the base of the jet at an angle from the linkage, the left and right carbs are the mirror of each other so a left carb body need a left jet and vice versa. SU call them front and rear rather than left and right because everything is named based on an inline engine (same as the cylinders, front plate, back plate etc). The jets for singles are a different length, I believe they are longer but I'm not certain I'm remembering that right, but they are different. I understand it's because the singles and twins have different amounts of choke travel, goverened by the jet rod and the choke lever. If you setup the wrong length of jet with a given choke lever and jet rod the jet will never be at the proper position. There are also two different bores of jet, but all Minis use the same size. SUs are all about the jet and needle relationship under a given amount of manifold depression and it's all designed into the physical parts so you have to get the right parts for the application. Having said that, you don't choose jets based on the exact engine tuning, as Roy says that's what the needle is for. You choose jets based on the broad application, you just need a pair of twin carb jets for a Mini. They are a green and a pink.

[surfblue63]

You could always buy your parts direct from Burlen/SU, it's where Mini Spares will get them from.

http://www.sucarb.co.uk/

[thebullet]

Amazing answer, thank you very much!

Now, David Vizard's carb chart suggests I use the blue jet. Why do Mini spares only sell pink for twins?

Edited by thebullet, 10 February 2012 - 10:53 PM.

[thebullet]

You could always buy your parts direct from Burlen/SU, it's where Mini Spares will get them from.

http://www.sucarb.co.uk/

Good idea actually, struggling to find twin jets on there for the cooper car, I have put that because of the head I have.

[surfblue63]

The blue colour that Vizzard referes to is the piston springs within the carb, not the jets.

Edited by surfblue63, 10 February 2012 - 10:59 PM.

[thebullet]

AH, my mistake! *continues to read*

If anyone could head me towards what I nee for my twin HS2's with my cooper head on that site, I would be ever so thankful!

Edited by thebullet, 10 February 2012 - 11:05 PM.

[surfblue63]

This is the link for the 1964-69 998 Cooper

http://www.sucarb.co...ProductId=10835

Also if you read Vizzard, he has some suggestions for the needles for differring engine specs.

[thebullet]

I did find this, just wasn't sure if those jets were suitable for twins.

[Dan]

Not many people will need a larger jet, so they wouldn't sell many. Mini Spares have both the pink and green but if you want the fatter one and its pair (can't tell you what colour that is just now, can't find my Burlen book) then you can get them from Burlen. You won't find parts on Burlen's website if you are tuning, unless you know the part number. Their online system only deals with standard setup, it has to as there are way too many possible options for tuning. Just phone them and ask, they are very helpful.

I should also point out that I'm not certain the difference in jet lengths is for the reason I mentioned above, that is just something I have been told. It's also possible it could be determined by the mounting angle as that changes the fuel height in the jet, but I think HS2s are always mounted at 30 degrees in the Mini whether they are single or twin. I think HS4s are at 20 if mounted as a single. Or it might be just the fuel pipe that is different and not the actual jet. But there are dozens of different choke levers that are all different so there must be differences. I just know that I have fixed many small problems by using the prescribed parts when presented with a set of twins that were built just using what someone thought was universal.

[surfblue63]

If you're unsure you could always email or phone them for advice.

[thebullet]

Might give them a call yes, thanks very much guys!

Very helpful info Dan as always.

Taken some notes and ill do some more research :)

[oltonlad]

as for the needles, put a pair of gy needles in the carbs and get the car to a rolling road to optimise them, its bad practise to "guess" needle choices, everyone uses different specs on their engines, even 2 identically tuned engines could very well need different settings to make them run at their very best, a session on the rolling road is the only answer.