twin HIF38 needles and springs...

[tedmcedd]

I have a HIF38 on my 1330, and it runs, but is lean in the high revs....

I bought another HIF38, and have made adapter plates for a HS inlet manifold and so have made a set of twin HIF38's

I now need to match them up, springs and needle wise, something like.... then if it runs I'll drag it to the rolling road...

are HIF38's the same needles as HS4s??

Ed

Edit: its a +30 1275, ported head, perhaps a cam of some sort??

I dont really know, I thought it was standard until I did a head gasket!

[Charlynsane]

What's your cam?

[ianh1968]

"are HIF38's the same needles as HS4s??"

More than likely, the HIF38 will have a sprung needle, whereas the HS4 could have either a sprung or a fixed.

The sprung needles are generally 2" long and the fixed needles are a few indexes shorter. The needles in both of
these carbs will be 0.090". If you want to fit a sprung needle in a fixed type carb, it is possible with a small amount
of work. Firstly, the collar needs to be removed from the needle, or the other way round.... Normally dropping the
needle assembly into the slightly loose jaws on a vice and then tapping the needle out of the collar with a small
pin-punch will do the trick.

The needle in the collar is a knurled/interference fit. To put the needle in a fixed type carb, the knurling must be
smoothed off.

FAILURE TO DO THIS MAY MEAN THAT THE NEEDLE WILL BE VERY DIFFICULT
TO REMOVE FROM THE DASHPOT AGAIN ONCE IT HAS BEEN PUSHED IN.

You may want to have a look at the Needle Selection Tool which can be downloaded from the Technical/Carburation
section of the Mk1 site. It's a spreadsheet document for comparing needles and it is in OpenOffice/LibreOffice format.

[tedmcedd]

What's your cam?

I have no idea!

I only found out I had +30 pistons and a ported head when I changed the head gasket!

I will have a look for the needle chart, they are the sprung type needles yes...

Is it worth changing to fixed type?

Ed

[ianh1968]

What's your cam?

Is it worth changing to fixed type?
Ed

If you have a pair of HIF38's, they will most likely be sprung needles. Unless you have a good reason to,
there would be no need to change to the fixed type. It would be possible to do this, given enough skill
and determination, but you would need to ask yourself "Why?" As I said before, it is possible to put a
spring type needle in a fixed type carb reasonably easily, but again, if there are needles from the correct
range available then it makes good sense to use them in the first instance.

The whole point of the spring type needle was to rid us of the need to centralise the jets on our carbs.
Given that the jet is 0.090" and most needles at the "fat" end are 0.089", there is theoretically only a
half a thou gap round the edge of the needle with the jet wound fully up. From this you will see that getting
things centralised is important if the needle is to run freely in the jet and not jam up at low throttle openings.

This was the benefit of the spring type, which are self-centralising. The downside was that the needle is
ALWAYS touching the side of the jet, so the needle would wear the jet oval over time as well has being
worn itself. Over time this would richen the mixture.

How have you deduced that it is running lean at the top? And what do you mean by the top, high revs at
wide open throttle, or just high revs at cruise? Where this would equate to on the needle would be in a
completely different place from one scenario to the other...

Methods of checking the mixture:
A "plug pull" after a good thrash? (Unreliable/hit-and-miss)
Using a "ColourTune" and just revving the engine? (Engine not under load, so useless)
Using a mixture analyser?
Using an engine dyno or a rolling road?

The last two are the only real ways of deciding on the mixture. Sometimes a retarded ignition can give the
same sort of hesitance that would suggest a weak mixture.

You have already suggested that a trip to a rolling road is in order and I am sure that if you have a good
operator who knows about SU carbs and their needles and springs you should be OK. Do not forget that
the way to evaluate your dyno session is purely and simply a before and after comparison. If you are not
happy that the figure is high enough, sure, go to a dyno which gives a higher reading, there are plenty of
those about. Also be sure that the engine temperature is kept about the same from one run to the next.

DO NOT UNDERESTIMATE THE FUNCTION OF THE SPRING, IT CAN MAKE A BIG DIFFERENCE....

Here's a true story:
Many years ago I went to a dyno. Once I got there, I found that the op had NO needles and NO way or
changing the curve in my dizzy. He "power" timed the engine at 6000RPM at xBHP at the wheels. He then
went for a cup of tea and quite a few biscuits. On return he operated his "Magic Finger" under the bonnet
and came up with another 10BHP, just like that. He was stupid enough to think that I would not know that
this increase was purely because the engine was now much colder. "OK", I said, "Now try this..." and I
pulled the heater control knob, thus shutting off the heat to the inlet manifold... His eyes popped out on
stalks when this gave another 2.5BHP, there was a knowing nod, and yet another tool was added to his
box of magic tuning aids.

To finish off, we took the car for a test drive, and, what a surprise, it pinked. The fix was to put the dizzy
back to exactly the same position that it was in to start off with. I was stiffed for £50, my engine was exactly
the same before and after, and I had wasted half a day.

So if you are reading this "Mr Turbo Torque" of Burgess Hill, Sussex, I hope you are still in business!


Tread Carefully, and Good Luck!