6 replies to this topic

[JCP]

I have a set of twin SU HD4's that I'm contemplating using on a 1275 (+20 thou over bored) bare shell rebuild,
Does anyone else have these fitted, if so what fettling is required? If you have a pic you could share that would be great.
Or if you have had experience with and don't recommend them, can you share why please.
Thanks all.

[carbon]

The HD4's are quite a rare beast. From what I have read they are like an upmarket H4 without the leaky jet seals, but also subtly different in how the idle mixture is adjusted. Might also be worth checking if the HD4 rebuild parts are all still available, Burlen are normally very good but some of the rare SU carbs may not have all parts off the shelf.

 

Main area to check is for clearance between carbs and bulkhead when fitted to the inlet manifold. There's not a lot of space and would be a great pity to do full refurb and then find the jet housings clatter against the bulkhead.

[JCP]

Thanks carbon, have checked the Burlen site, and they still supply overall kits and a majority of replacement parts which is good.
I'll have to do some measuring before I start welding the shell together, will be far easier making some adjustments to the bulkhead (if needed) while the panels are off, as you say don't want to do a full refurb then discover they foul up on the bulkhead.

[carbon]

There are some good dimensional drawings of HD carb on the Burlen website: http://sucarb.co.uk/...su-carburetters

 

Looks like the distance from carb centreline to bottom of the float chamber assembly is 3 inches. Not too different to the H4 or HS4 carbs.

 

Other consideration is that to clear bulkhead you will probably need inlet manifold with 30 degrees downdraft, if your float chambers are not already set for this angle then replacing them may start getting expensive.

[JCP]

That's most helpful, Appears I've overlooked some important but essentially basic stuff, more than just a quick measure and some cutting.
Will have to take a step back and make sure I take everything into account before spending any money, and potentially cause myself a lot of grief. Won't lie, I got a bit excited about having a set of twins under the bonnet, think they look great.
I shall do some in-depth research, (cost, labour, modification req. etc) and providing it is viable, install them and post up a build and cost list, or if not viable I'll post up here why it wouldn't be a good idea to fit them.
Hopefully I'll get some positive results and be able to build a cheeky little engine with them, well fingers crossed anyway.
Thanks again carbon :)

[carbon]

If you want a set of twin SUs for a fast road 1293 then I would recommend getting a set of twin HS2s and then rebuild following Vizards instructions on carb and inlet manifold modifications to get flow rate close to HS4 level. Use with pair of decent K&Ns and you won't go far wrong.

 

If properly modified the indications are that vizarded twin HS2s are not going to lose you more than a couple of hp at around 85bhp at the flywheel compared to twin H4 or HS4.

[JCP]

An update so far- the carbs I have came off an MG magnette, and were used between 1961 and 1963, the float chamber angle on them as standard is 45 degrees, and to buy a 30 degree float chamber will cost approximately £100 each, on top of that I would want to buy a full overhaul kit with replacement needles (no.3 or 4, a rolling road session will determine which is more suited) and springs (red), so all in all the cost so far is edging up to £500, this is before having to modify and adjust them to sit on a suitable inlet manifold.
Now if money and or time is no object (and I'm certainly not in any hurry at the moment) yes they can be fitted, however for the time and money I believe it would make more sense to buy a full working set of twins with manifold that are already suited for the mini. As stated above by carbon a set of twin HS2s rebuilt to vizards instructions will be more suited to mine as it will be a road car.
However if you've got the funds and are building a track car/ hill climb etc they could prove to make a punchy little motor.