Spitfire HS4 Carb

[dunketh]

Righto, after being given a Mini 2in1 manifold I've decided to dig out my spare Spitfire 1500 SUs.

Here's what I want to do.

Fit a single Spittie 1500 SU to the mini manifold then attach to the minor.
Due to reasons of cost I'll still be keeping the standard morris exhaust and attaching it to the mini manifold in the normal way.

The needle in the spit carb is an ABT.
Will this work OK with my standard 1275 engine?

I can rob any fittings missing off the old spit SU from my old HS2 so thats no problem... its just the needle that concerns me.
Also, the spit SU has a large plastic 'vent' pipe attached. Should this go to the breather pipe from my chain cover?
And.. theres nowhere to attach the dissy vauum pipe to. Does this matter?

[Kevin]

I thought that twin SU`s were designed to work in pairs one left and one right handed are they really suitable for single use ?, a second hand 1 1/2" HS4 - HIF 38 or 1 3/42 HS4 - HIF 44 isnt going to cost that much, has the giver of the manifold something more suitable.

[RogerRust]

There is a program called WinSu. You put all the details in -engine - head - cam - carb - air filter - exhaust etc and it tell you which needle is best. Its only £10 but I keep hoping someone here will have a registered copy.

[d_harris]

I'm just waiting for my CD to arrive! Had a play with the demo and seems really useful.

[RogerRust]

Dan let me know when it arrives I'd be interested as to how it goes?

[Welung666]

I have a copy somewhere, just not installed it back since my last format

[Packedup]

The needle in the spit carb is an ABT.
Will this work OK with my standard 1275 engine?

Pass. It's suitable for a 1500 Spit, so I'd imagine it'll be wrong, but how wrong I don't know.

I can rob any fittings missing off the old spit SU from my old HS2 so thats no problem... its just the needle that concerns me.

No you can't - The bracket for the cables is different, the Spit carbs won't even have one (because they have the linkage bars) and the HS2 one won't fit... However, one suited to the carb you use should be easy enough to find (Mini for the HS4).

Also, the spit SU has a large plastic 'vent' pipe attached. Should this go to the breather pipe from my chain cover?

Pull the pipe off and you'll find the normal brass pipe beneath it. Use whichever setup suits your exisitng breather pipes

And.. theres nowhere to attach the dissy vauum pipe to. Does this matter?

That's cause the dizzy take off is on the other carb on those!

I might be able to find a single HS4 (off a Dolly 1300 so should be a closer match) somewhere - Might be interested in working a swap for the twins?

One other thing, if you have waxstat HS4s, then go the 2p mod route on the one you fit as waxstats are nasty little things.

[dunketh]

I might be able to find a single HS4 (off a Dolly 1300 so should be a closer match) somewhere - Might be interested in working a swap for the twins?

I'd be interested but won't have anything to swap.
The other 1500 carb went in the bin (long story, parents shed..etc)

The choke linkage on the carb is the same but the accelerator one is different. I'm sure something could be made up.

I've been comparing needles in WinSU and the ABT needle is a close match to several used by 1275GT owners elsewhere online.

Unfortunately WinSU is completely useless without registering. I have Version 1.5 which doesn't need registering but that suggests completely different needs to the new 2.5 version.

Still unsure about the vacuum take off for the dissy. Could I run without it?

Oh and thanks to 'packedup' for the manifold in the 1st place!

[Packedup]

I've been closely aquainted with twin Triumph carbs recently, can't picture it in my head properly though

The rear carb has the vacuum take off I think, and the float is on the left as you look at it from behind. So that's the "wrong" side on an A series install. The choke cable also has nowhere to go as the little bit of metal tube to locate it isn't there, is it? Though that's an easy fix.

You can run without the vacuum (let's face it, a lot fo cars do when the advance unit packs in! ;) ) but it's probably better to run with it if you have the option. Shame in a qway about the manifold, as there's some performance A series ones with the take off there instead of the carb.

Accelerator linkage - As far as I can remember the levery bit won't be fitted to the Spit carb (due to it using the linkage rods when normally installed) but you should be able to remove the cupped spindle nut and fit a normal HS4 lever/ bracket thing. You then need the big bracket that the cable is located by, which is where finding a Mini comes in handy

Shame I don't have my old HIF bits, a 38 would go nicely on that manifold and give you a nicer setup - Not sure how much the local breakers would charge for one, or if you'll even find a 998 Metro in them anymore!

[bmcecosse]

ABT looks horribly weak to me - AAA is more like it. And yes - you really should get a vacuum connection. Drill in and fix a little tube - good drive fit should do it - then attach the vacuum pipe.
The float bowl needs to be dead vertical when bolted on the manifold - is it ?

[Packedup]

The float bowl needs to be dead vertical when bolted on the manifold - is it ?

Unlikely, and good point.

Can't the little positional washer be replaced with the one of the HS2 to achieve that though?

[Alec]

Hello Dunketh,

have a look at the www.Burlen.co.uk website in their section for S.U. spares, you should be able to identify suitable throttle levers, float chamber mounting adapter etc. The float chamber will bolt either side but you will need a new adapter. (the HS2 one will probably suit anyway)

Personally I wouldn't worry about the vacuum advance as it is for economy. It will only benefit you if you get the carburettor set up for it using a rolling road. It's benefit is for long periods cruising at steady speeds which is rare on our roiads these days.

Alec

[bmcecosse]

Yes - you can usually either modify (or just turn over) the existing spacer for the float mounting - or buy another. Sometimes the little flexible fuel pipe is not long enough in the new position - I have had problems with this. The vacuum advance on the dizzy 'brightens' the whole engine - makes throttle response better going from off (high vac) to on (low vac) smoother as the ignition is held advanced for that second or so. It also comes in to play as soon as the car is started - pulling the timing up with the high vac in the inlet manifold at idle - without it you will need to set more static advance which in turn could lead to starting problems with the engine kicking against the starter, and pinking when slogging under load. Try your best to get it connected - it's really not difficult. And it does help economy.

[Alec]

Hello Bmce,

personally I have never noticed any difference and my current Triumph 2.5 doesn't even have one, i.e. the bellows assembly on the distributor.
Bear in mind that you need to set the carburettor on the weak side at cruise for it to have any economy benefuits, otherwise its may even over advance which is why I refered to setting up on a rollling road.

Remember the MGA twin cam, it was the vacuum advance at high revs that knocked the pistons out.

Alec

[bmcecosse]

Well - it would only advance on a closed throttle - so surprised it would do any harm running like that. Never heard of that problem with the TC MGA (plenty others though!) - maybe just one of those stories that comes and goes. Most cars have tha vacuum advance - it's by no means essential - but it is there for a purpose.

[Alec]

Hello Bmce,

no, that was the problem, it used to advance at high revs (it was not designed or meant to) doing the engine no good at all. It gave the MGA a lot more performance than the basic 1500 or 1600 'B' series engine and was also a lot faster than the MGB that followed it. BMC gave up on it because of the engine troubles. Unfortunately, at that time strobe timing lights were not available or they might have solved the problem.

I do realise that it is there for a purpose, but is less relevant to someone who drives hard, as I assumed Dunketh is, as he is modifying the engine for more power.

Alec

[bmcecosse]

Yes - the twin cam head gave much more power - but have not heard the advance story before. Nowadays - they fit the Vauxhall dohc engine in B's - now they really fly!! Way more power (and revs) than any B series can manage.

[Packedup]

Vauxhall engine in an MG. Philistines.

What's wrong with putting an M or T series (or even 8 valve O series, maybe in EFi form) in there, at least it's pretty close to what the makers intended!

[bmcecosse]

I know I know - but let's face it the Vauxhall engines are terrific - and the O/M/T engines are pretty cack!

[Kevin]

Back to the topic it looks like it will be much simpler and cheaper to get a mini or similar 1 1/2" or 1 3/4" SU to solve your issues rather than spending money modifying a carb that is not really suitable in the 1st place.