8 replies to this topic

[Cheeser]

I have mildly gas flowed a pair of HS4s that I use successfully on a 1380 , just genenerally smoothed, removed the valves on the butterflies and fitted a good stubstack.
Just about to build a similar size engine and have aquired a pair of Hif 4s from an MGB, started taking them apart and suddenly found a groove in the bottom of the piston together with a 'channel' on the bridge behind the jet.
Should I continue with these carbs and modify them in a similar way to the HS4s, do I leave the bottom of the piston as is and also leave the area after the bridge behind the jet?
Any of your thoughts and experience of twin Hif4s will be most welcome, I know the linkages will have to be shortened/modified
Thanks

[DeadSquare]

I suspect that SU know quite a lot about their carbs and probably didn't include those features in error, so before you obliterate them, try the MGB carbs on your car to compare them to the ones that you have improved, and let us all know your thoughts.

[Spider]

Given that in stock form, twin HIF44's are suited to Engines in the 110 - 180 HP Range, on that alone, fitting them to just about any road going Mini wouldn't be the wisest move and even for Competition, there's better ways of getting the job done.

 

I've never been in favour of 'gas flowing' SU carbs, in particular the Piston and Bridge, as the shape and design of this area of the Carb works hand in hand with the Needle Profiles & Dashpot Springs so that when the Tune of the Carb is sorted, the Fuel / Air Ratio is right not only for Max Power but also on Cruise.

 

If one really finds they need more Air Flow through the Carb, go up a size in the Carb.

 

'Gas Flowing' SUs is done for some classes of competition, where either the original Carb had to be retained, or the original make of Carb. Clearly, for this purpose, we are not concerned with how the Carb performs on the Cruise.

[GraemeC]

He’s asking about HIF4 not 44 Moke - they’re 1.5”

I ran these on my 1380 with no mods and they’ll be going on my 1460, again with no mods.

[Spider]

He’s asking about HIF4 not 44 Moke - they’re 1.5”

I ran these on my 1380 with no mods and they’ll be going on my 1460, again with no mods.

 

OK cheers there Graeme.

[nicklouse]

Never having seen any HIF4s I would ask is this a factory groove you are talking about or has someone got the hacksaw out? If factory I would not be concerned.

[Fastorq]

Never having seen any HIF4s I would ask is this a factory groove you are talking about or has someone got the hacksaw out? If factory I would not be concerned.

I agree with above
Been modifying and rebuilding Webers and DellOrto twin duals for over 20years for road/race/DT turbo use etc and only recently started playing with the SU family.
to be honest I’m surprised that in stock form they punch so well above their weight, performance wise (maybe HS2 twins are a wee bit disappointing and limiting)
Although carbs are quite old technology they do a very simple job and SU knew what they were doing.
You have a wider range of “bolt on” tuning modifications with Webers and Dells so don’t really need “fettling”
Best just to leave factory as is with your SU carb.

Regds
DavidR

[carbon]

Never having seen any HIF4s I would ask is this a factory groove you are talking about or has someone got the hacksaw out? If factory I would not be concerned.

Some HIF4s have this groove in the piston, have only seen in photos as the HIFs are a bit modern for my liking.

 

This groove looks about 6mm wide by 1mm deep and may be to improve mixture under light load conditions - help prevent lean surge.

[nicklouse]

 

Never having seen any HIF4s I would ask is this a factory groove you are talking about or has someone got the hacksaw out? If factory I would not be concerned.

I agree with above
Been modifying and rebuilding Webers and DellOrto twin duals for over 20years for road/race/DT turbo use etc and only recently started playing with the SU family.
to be honest I’m surprised that in stock form they punch so well above their weight, performance wise (maybe HS2 twins are a wee bit disappointing and limiting)
Although carbs are quite old technology they do a very simple job and SU knew what they were doing.
You have a wider range of “bolt on” tuning modifications with Webers and Dells so don’t really need “fettling”
Best just to leave factory as is with your SU carb.

Regds
DavidR

 

good you have seen how good the SU is and also how simple it is. it will out perform most carbs in every day use but as it cam as standard most people dont rate it. more fool them.