27 replies to this topic

[MIGLIACARS]

Nothing beats the look of twin hs4's :)

I beg to differ h4 s

[AlexMozza]

Nothing beats the look of twin hs4's :)

I beg to differ h4 s

Fair enough, got twin H4s in the MGA,
The linkages do look the dogs bits though !

[Chris1992]

I had twin HS2s on my 1275 and they were an absolute nightmare. Never have I hated something more than those damn carbs... switched to a nice big HIF44 and not only is it so much simpler and more reliable, but I actually have more power too. I do miss how the twins looked but that was the only advatage 

[InnoCOOPER]

What do you want close ups of?

Any pictures of the Throttle assembly and choke assembly if poss.   Fixtures of cable etc  just to give me an idea of how the best way is of fixing them.  I plan to use std throttle linkages and shorten.  But you mention the throttle butterflies open the wrong way?   Any help appriciaited

[GraemeC]

Sorry - forgot to reply to your PM.
Ive got a couple more pics, just need to upload them.

[Minigman]

Ive found you get better throttle response from twin set ups. Go for it I say.

[carbon]

+1 for above, I have found twin HS2s work very well with a 1293.

 

All I would add is be careful about how crankcase ventilation is plumbed in with twin carbs. Using the original PCV (clack vave) with a modified motor may draw too much air, and makes setting up the mixture a bit tricky. I have stopped using the PCV and gone to the later set-up where the crankcase vent pipes connect to the sides of the carbs.

 

And check the thickness of the inlet manifold flange at cylinder head face is the same as the exhaust manifold flange.

[hhhh]

HS2s on an otherwise stock 1293 might work well, but above 70HP you're going to be running out of breath.

[Shooter63]

HS2s on an otherwise stock 1293 might work well, but above 70HP you're going to be running out of breath.

Behave.

Twin hs2's will make 100bhp, all it means is you are losing a few brake up the top end over a bigger set of twins but you gain snappier throttle response over the twin 4's which are still better than a hif44.

Shooter

[Shooter63]

This is how I modified my hif4 carbs that came off a mgb
Take the nut and 2 levers off the throttle spindle, reverse the way the 2 levers go on ( you need to file the hole out a bit on the lever that now goes closest to the carb ). File down the nut to give you more clearance,do this to both carbs obviously cut down the spindle to fit.
Finished
As I don't like to be cramped up I moved the throttle lever to the end of the R/H carb
Cap off the breathers

Shooter

[InnoCooperExport]

I think Vizard also mentions that twin HS2's can be made to flow better than a single big carb with some minor mods. These include modifying the inlet manifold which has some big square edges inside which cause vortices as well as a few small tweaks inside the carb IIRC.

[carbon]

There's quite a bit of detail on this topic of modifying SUs and the twin inlet manifold in Vizard's 'Tuning the A-Series'.

 

Modifying the HS2 can help them flow better - thinning the throttle spindle and cutting the throttle plate screws off flush gives quite a bit more flow without upsetting the mixture. Any mods to the HS2 throttle or piston with improve flow but also change mixture settings.

 

The standard BMC twin inlet manifold is not great, follow the instructions in Vizard's book. Or get the suitably sized Maniflow twin manifold.

[Spider]

There's quite a bit of detail on this topic of modifying SUs and the twin inlet manifold in Vizard's 'Tuning the A-Series'.

 

Modifying the HS2 can help them flow better - thinning the throttle spindle and cutting the throttle plate screws off flush gives quite a bit more flow without upsetting the mixture. Any mods to the HS2 throttle or piston with improve flow but also change mixture settings.

 

The standard BMC twin inlet manifold is not great, follow the instructions in Vizard's book. Or get the suitably sized Maniflow twin manifold.

 

That's true enough regarding the internal mods to any Carb, however, I found some time ago that those, particularly to the shape of the Bridge, affect the characteristics of the Carb and the zones of the needle that it uses between Wide Open Throttle & Cruising where the 'designed' balance between these is lost.

 

Also, after having tried this, and reflecting on it, it's easier to just go up a Carb Size.