SU HIF6 carb

Paul Goldsmith

Paul Goldsmith

0
I've just picked a NOS SU HIF 6 carb quite cheaply, it seems a good 'un on visual inspection.

I made the big assumption that subject to a suitable manifold that this should be suitable for the 1725cc engine - hopefully our aluminium headed block waiting to be transplanted :D

I'm no expert on these things but I guess that the needle / jets (wow, I almost sound like I know what I'm talking about ;)) might need replacing to suit the Commer application, so my questions are ;

How do you do know if a different needle / jet is required ?
If so, where to start in identifying which one ?

I've found some NOS Hillman Hunter SU jets and wondered if they are generic enought to suit the HIF 6 and whether likely to be appropriate for the Commer

Any advice greatly appreciated


th_Commer_carpark.jpg

Commer 'Hi Tor' by TorCars
 
Look back a few pages (page 36) on BOTG to see the set up I'm using. Tim made up a manifold for the ali head but there is a bit of chopping and modding to get it in the engine bay - but it will be worth it. The mod for the Iron head is a bit simpler but needs inlet and exhaust manifold work (bronze welding) but commeracer can help you there - check out 'Jessica's Xmas Pressie' to see bigmonkeyman's progress on that front.

'Harvey the RV'
 
I started with a HIF6, the type with a fixed needle - or it should have done - I had terrible trouble trying to get one to fit, in the end bowed to Tim's advice and got a HIF 44[8)].

'Harvey the RV'
 
right lets start at the beginning, hif6 is perfectly suitable for commers [^]
jets are not changed on su carbs, all the tuning is done on the needle, so forget jets.
best starting point is whatever you have got in the carb.
the needle is divided into 13 segments each of which control different parts of throttle opening, i.e the first 3 control idle the next 5 mid range, the next 5 top end.
there is something like 120 different ones available, so what you do is try one, see where it is rich or weak and then check a needle chart looking for one that is fatter or thinner in the appropriate area. they generally change in size by about .002". so it can actually have more "metering sites" than some fuel injection systems :p. a good rolling road guy will sort it very quickly and precisely, or blast up and down until it feels right :I
what you had panky was a hs6, the hif 6 is 1" bore plus 6 1/8ths of an inch = 1 3/4". the hif44 is just a later metric version 44mm bore (about .020" smaller)
so that should clear it up or confuse even further :D

"you were only supposed to blow the bloody SLIDING doors off"
 
Burlen Fuel supplies a needle guide with the width of different needles at the various points of measurement. I think mine came free with some parts when I asked for one - it maybe on their site somewhere. With a good micrometer you can start with a thick needle and taper it down gradually with a nailfile (they are only softish copper compound).
Just remember that you can make it thinner not fatter, once you have filed too much away its hard to put the filings back on [B)]. Then you have to start with another needle. Saves buying needles to experiment at £9 a go. Worth doing if you're as tight as me:I


The springs should be matched to the needles too. They cant be hand modified but fortunately there is a only a choice of about 5 of them ;)



Cheers
Jules

RatSport www.ratsport.co.uk
 
Thanks for all that useful info folks - good to know I've got a good base position to start from :)

I'm learning loads all the time that's to this forum - cheers !

th_Commer_carpark.jpg

Commer 'Hi Tor' by TorCars
 
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