replacement for twin suhs2 carbs on my 1275 midget

Post by **ssnjimb** » Tue Sep 29, 2009 11:04 pm

Hi

Iam looking at replacing the troublesome twin su hs2 carbs on my midget he is the 1275 version.

Iam looking at the single carb version as trying to tune those two is making me angry.

I dont want to lose any power really so will the hif38 be too small

James

Post by **PSL184** » Tue Sep 29, 2009 11:09 pm

Ideally you will need a 44 although it will probably only be top end that you'll loose running a 38.....

Post by **ssnjimb** » Tue Sep 29, 2009 11:19 pm

thankyou psl. trying to get the mixtures the same and the air balance the same then having to adjust them GRRRR lol lol

I want it simples

Jamie

Post by **PSL184** » Tue Sep 29, 2009 11:33 pm

yep, twins can be a real PITA

Post by **bmcecosse** » Tue Sep 29, 2009 11:50 pm

They shouldn't be - easy to set up twin SUs. Use the lift pin to set mixture and a length of hose for the idle ! But you are right to think a big single will be better for power - HIF44 on an MG Metro inlet manifold. BDL needle - and it will be fine!

Post by **MarkyB** » Wed Sep 30, 2009 9:16 am

They would be easy to adjust if the mechanism wasn't so crude.
I found the rod and clamp set up very tricky to do fine adjustments to, takes ages to get it right and a little to much pressure and they are miles out again.
If they had included something with a screw and locknut it would be easy to do accurately.

Post by **ssnjimb** » Wed Sep 30, 2009 9:57 am

Another drone is if one isnt acting how it should its hard to tell which one it is.

Iam going to replace them with a hif 44 on the metro bmc has prescribed

Jamie

Post by **mike.perry** » Wed Sep 30, 2009 1:16 pm

Twin SUs look better. Mine are somewhere near balanced, I used a colour tune. I must admit that I have been tempted to swap them

Post by **bmcecosse** » Wed Sep 30, 2009 2:28 pm

To balance the carbs - just slighty slacken the linkage between the carbs - then set the idles on both carbs so they sound the same when listening to the intakes with a short length of 1/2" bore hose held in one ear. Then gently and carefully tighten the joining link - small spanners obviously help here. Mixture is tested with the 'lift' pin - until both carbs react the same. Very probably need to reset the idle speeds after that! People say the carbs go 'out of tune' - but that has never been my experience with twin SUs. Why would they ?! The single HIF44 will give better performance - but keep the twins safely - because when you eventually sell the car - the new owner may want the originality of the twin carbs.

Post by **MarkyB** » Wed Sep 30, 2009 6:30 pm

Why didn't I think of that?
Even when not balanced to perfection the performance of my 1275 was much better with the twin carbs fitted than with an HIF44 but then I never changed the needle in it so maybe it was miles out.

Post by **bmcecosse** » Wed Sep 30, 2009 9:36 pm

The HIF 44 must have been bad! Should be much better than twin HS2s