Correct position of the needles on HIF6 carbs (1974 V8)

DamianZ28

DamianZ28

Active Member
Hi All,
Car has been running good but not great, carbs are just not set right & I think it's the needles not located correctly in each piston, fitted new needle holders a while ago as once was missing before I bough the car! Improved heaps but still sounds like it doesn't have the right balance of fuel/air, I took these pics and you can see the outer collar (?) that the each holder sits it isn't the same setting, the right hand carb piston has it proud of the groove while the left hand piston has it flush with the groove, I have tired to get both needle holders level with the bottom of each piston which improved running but what is the correct setting? any pics will help,
I guess new needles help as these are possibly originals so 49 yrs old.
Many thanks Damian.
 

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Hi Damian,

The collars are supposed to be flush with the base of the piston, not proud of it. The guide marks on the collar and piston align allowing the needle to receive the correct bias. The reason why one collar sits proud is most likely due to being incorrectly positioned initially, the grub screw tightened scoring and indenting the collar. Now each time you place the collar correctly, upon tightening the grub screw it returns to the incorrect position owing to the prior damage. The best way to correct the situation is to replace the collar, or better still replace both collars.

Ron.
 
Hi Ron,

Many thanks for the reply :), I removed both grub screws to remove the needles and the new holders I fitted last month but the collar that is proud of the recess will not move any further back into the base of the piston which is PIA, are they meant to move easily or are they fixed in anyway ?

Cheers Damian.
 
Hmmm, that is certainly a pain! Are both collars the same length? I seem to remember having seen two collars of different lengths but maybe I am imagining it.

There is nothing within the piston that is preventing inward movement of the collar? The collar needs to be flush else your needles are at different heights which means your air fuel ratio for all engine speeds will be different for both carburettors.

Ron.
 
Hi Ron, its possible, I'll measure them individually, possible the pistons are not original seems the car is 49 yrs old. I've tried to adjust the needle heights but it's just not happening as its all over the place lol. Ideally a good pair of second hand ones may help.
 
Sorry yes nothing l could see to make one collar move but they are definitely not sitting the same, one collar is proud and one is sitting flush in bottom of the piston.
 
It might be an idea to give Burlen a call over at Salisbury. They really are SU specialists and aren't too far away.

Richard
 
I had the same issue when I was restoring my car. My trusted mechanic at that time was having trouble tuning the engine to run to his complete satisfaction, so he decided to investigate in more detail. He had the two carbs off and apart, all the components cleaned and laid out neatly on his workbench. He pointed out to me how somebody had previously fitted the HIF6s with a variety of mismatched parts! The needle collars (or whatever those bits are actually called!) were not identical, and were of different length. We got various new bits'n'bobs from Burlens and he got it all working pretty nicely in the end. I dimly remember he explained something about the needles being 'biased' and that "over time they had worn a slot or groove" in something else (!!??) – was that in the collars – I'm losing my memory. :(
A decade or so later I had to repeat the process including having the bodies ultrasonically cleaned and the dashpots polished, but that's another tale which I think I've already recounted in my thread somewhere else on here.
 
Hi guys, yes I think mine are mismatched, I cannot move the proud collar back into the recess any further so with the pair of them not matched its no wonder the car will not run properly/smoothly. I have managed to get a spare piston with the collar correctly seated from Jeff at Wins so will see if this will sort the running! thanks for all the help though :) :thumb:
 
The bias on the needle makes it rub against the jet and eventually will wear a small crescent shaped pattern on its edge increasing area which is most noticeable at idle when the rest of the orifice is restricted by the needle. At full throttle the percentage increase is very small . I spoke to SU when it was still part of BL at Wood Lane Birmingham about the poor , especially idle, running of my 2200 P6 (Circa 70K miles) in about 1977 and they explained this and suggested I changed the jet . The wear on the needle is spread over its whole length and was advised there was no need to change that as well . Immediate improvement , job done.
 
Hi all, thanks for the input Roverp480, I will get new jets ASAP but also may go down the weber 4 barrel conversion but not for while yet due to the bank of wife, but jets yes as these are original so nearly 50yrs old.
Have fitted the 2nd hand piston with the correct flush fitting collar & its much better but not 100% , I used the old needle holder as I noticed the brass replacements I fitted made the needle sit off centre when the grub screw was gently tightened, also on one carb it prevented it from moving up & down smoothly when the dashpot was refitted, I swapped it back to the old one & the needle sits in the centre & the piston moves freely now, so one carb has the old needle valve holder & the other still has the new brass one which is making the needle off centre & lean toward the small dot indentation of the new holder (see pics above) . Would this effect the running/air fuel mixture due it not being centre in the jet tube ?
Good Jeff at Wins has posted me a good 2nd hand one so I'll fit that & see what happens.
 
Hi Damian,

The HIF6 carburettors feature swinging needles within their pistons. Each collar features a heel and the little spring atop the needle once fitted into the piston results in a biased needle. If you push against the bias you will feel the needle and spring back upon removing your finger. They are supposed to be this way. This means that the needle is offset within the jet and not centred. Earlier SU carburettors featured fixed needles with centred needles within the jet.

Ron.
 
DamianZ28 said:
Hi All,
Car has been running good but not great, carbs are just not set right & I think it's the needles not located correctly in each piston, fitted new needle holders a while ago as once was missing before I bough the car! Improved heaps but still sounds like it doesn't have the right balance of fuel/air, I took these pics and you can see the outer collar (?) that the each holder sits it isn't the same setting, the right hand carb piston has it proud of the groove while the left hand piston has it flush with the groove, I have tired to get both needle holders level with the bottom of each piston which improved running but what is the correct setting? any pics will help,
I guess new needles help as these are possibly originals so 49 yrs old.
Many thanks Damian.
Click to expand...
The needle retaining collars are supposed to be flush with the base of the piston, not flush with the base of the groove.
Both the piston assemblies in these pictures will work if you release the grub screw and let the needle come out of the piston until it is flush with the BOTTOM of the piston.
 
DamianZ28 said:
Hi guys, yes I think mine are mismatched, I cannot move the proud collar back into the recess any further so with the pair of them not matched its no wonder the car will not run properly/smoothly. I have managed to get a spare piston with the collar correctly seated from Jeff at Wins so will see if this will sort the running! thanks for all the help though :) :thumb:
Click to expand...
The needle collars are supposed to be flush with the VERY BOTTOM of the piston
 
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The needles are supposed to be spring biased to one side, it will either be toward the throttle plate, or away from it, the marking on the collar is there to set this bias. You need to find out which way the needle should be leaning for your application.

You should not mix and match air slide and carb body assemblies.

If you set the needle collars correctly so the collar is flush with the VERY BOTTOM OF THE PISTON you will be correct.
 
Hi All, Sorry for my late reply but many thanks for all the input, much appreciated :). Fitted original needle holders back to both pistons and set them so they are flush with the very bottom of the piston & not flush with the base of the groove. The outer guides/sleeves are still flush with base of the groove and not the very bottom of the piston as per advised with the needle holders, these seem to be pressed in ? But still no change & still sound like it running on 6 on tick over & even when revving, doesn't sound like a V8 should :(. I have new jets to fit tonight so see if this'll makes a difference.
 
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