Simon Perks

Simon Perks

Active Member
https://www.moss-europe.co.uk/1500-needles-for-su-carbs.html

So it's running too rich, I need a leaner needle ...
Internet research directly has only yielded a Sweedish chap in 2005 who used an BCJ and BDJ ..
Err what?
Check this ..
http://www.mintylamb.co.uk/suneedle

Any the wiser? .. Me neither ..

So does anyone out there know .. what needle i need.
I shall contact the folks at SU.CO.UK and see what they say..
Otherwise i have to refit the old Zenith for the MOT!!
 
Please refresh did you remove your K&N

when you ordered your carb what spec did you give them, and do you know what needle is fitted?

it could just be a case of float level or setting jet up.

j
 
J,
We did indeed remove the air filter.
the carb is either fully closed or as soon as it's open it's way to rich.
So the way that the piston lifts the needle, or rather the distance that it's raised at idle has to have a needle
that restricts the fuel flow more .. or rather has a finer slope .. actually there are steps on the needle, variations in width and length of a step give a gradual increase or decrease in fuel
I need some in-between steps "zwischenstuffen"

The ACR SU kit that I bought has no paperwork to say exactly what it is fitted with and the part number
FZX 3019CK draws a blank on their website search.
The SU box has the words "conversion special" printed on it.
As they come in pairs for a V8.. I wonder if it is jeted as such.

Fingers crossed that the people at SU get it together and by the wonders of (insert favorite overnight service here)
next weekend will not be a refit palaver.

Simon
 
Problem being if you don’t know what needle you have, how do you know what needle you need.

There must be a chart on internet so you can check the measurements on your needle.

so are you saying it’s rich at idle?
Have you checked the jet is not too low?

been a while since I played with an SU:)

j
 
You have these things:
Jet size
Jet hight (the screw underneath) - is the jet adjustble in the throttle slide- with a clip?
Needle profile. The needle is not a single taper, it varies to give more or less fuel over the mid range, I think that's the letters. Some are stepped to match an engine the "gets on the cam"
(that's why they are showing you a graph)

You start with jet size and get full throttle right using jet size (at full throttle the needle is out the jet), then you set mid range on the needle/jet height, then you change the needle profile if you have flat spots mid range or poor pick up off idle.
 
So here we go ...
I currently have the BGB needle and as you can see the curve rises steeply after step 4.
We are trying BDB and BDM both of which have a leaner curve.
Stay tuned .. I will know more after the weekend how it works out.


needle-su.jpg
 
My only observation with your new choice is they are the leanest all up at the upper end of the range, which may not be best.

but good luck:) I suppose it can always be changed back after the MOT:D.

j
 
marjon said:
My only observation with your new choice is they are the leanest all up at the upper end of the range, which may not be best.

but good luck:) I suppose it can always be changed back after the MOT:D.

j
Click to expand...

Your quite right and the goal is to pass the emissions test, as you rightly say i can indeed afterwards put it back .. the garage did tell me to put the old Zenith back on for the test .. but thats a job i would rather not have to do if just the needle change helps

S
 
The two lean needles look to go very lean at high loads so they are risky for engine damage under full load. Unless they work great I would not leave either of them in once the test is done. The needle you have is odd, it seems to overfuel in the mid range, I suspect that BBW will be best on the road - it doens't overfuel in the mid range but fuels more at full throttle.
The only other thing I can think of is altitude, where are the tests being done? The weak needles would make sense at altitude but you would need to swap the needle if you came down to sea level.
 
First thing I would try would to remove the elbow pipe from the back of the carb to make sure its not upsetting things.

Don't forget that your emissions test will be performed with the throttle slide barely open (I assume the Swiss test is a no load test). If you look at all the needles you have referenced they don't start to diverge for some time, by the time the slide has lifted this far the engines probable near its red line with no load.

If this kit is for your engine you would have thought that the manufacturer would have done a half decent job of selecting a needle and needle jet combination to match the induction system and cam. If its the wrong needle then you may be better off booking a rolling road session, there are dazzling number of option to choose from. I remember having a rolling road session on an HIF SU equipped car and after going though a number of of needle options the guy filed a small flat on one in a particular area to get rid of a lean spot so I think they can be quite sensitive.

One other thought, you have got oil in the dash pot haven't you.
 
Cant quite decide what the effects of the oil would be on steady state running, none would be the gut feeling as its just a damper to provide transient enrichment. Still worth checking that you have some in their.
 
My concern is the upper end of the needle for the engine.

although the BDM needle seems to be the lowest at low throttle openings, (if I see the chart properly)

but what are the emissions test speeds for CH? I don’t know. Is it actually before the present needle “bumps up” as they are all very much the same low down, for a reason:)
I think the jet level still needs checking.
But it’s fun to play and learn :) Done plenty in the past, but it’s like riding a bike, you have to be there to hear/see what’s actually happening
Internet diagnostics is a very difficult thing to get right,

I hope @Simon Perks gets his MOT:)

J
 
Its coming back to me....I used to run a weak mixture - on the lean limit, and thick oil so it richenend up for acceleration to stop pinking. I was short of money - running a 3.4 Jag on a student grant - those were the days!
 
marjon said:
My only observation with your new choice is they are the leanest all up at the upper end of the range, which may not be best.

but good luck:) I suppose it can always be changed back after the MOT:D.

j
Click to expand...

Thanks Rob, Kane, Dippy, Marjon,
For all the advice, noted about the lean running and engine damage .. didn't think about that before now ..

I have to say that running on the present needle and a K&N air filter having adjusted by hand the SU( lifting dash pot causes no rise or fall in engine speed..) She ran really well, yes heavy at 90KMH on the motorway but on the 90KM of
offroad trials at a a maximum of 40 ro 50kmh it was surprisingly sparing on fuel consumption

For sure my last resort is to refit the Zenith (good job i didn't cut the throttle bracket as the LHD conversion recommended) and then flip it back after..

So the She is at my local garage who can issue the emissions certificate, they do this with the engine at tickover, so with the needle that came with the kit we can't get it down to 30% CO2
with the needle adjustment starting at fully closed a single turn open and the engine runs but the level goes off the chart...
Yes the mechanic there will check the seating , it made only sense from a time point of view to do this once we have the needles .. they came yesterday, he is an experienced guy who works on the local farming communities vehicles.

Yes the whole air filter assembly is off for the test.

Our average hight above sea level here is 1000m, low land Zurich is 400 to 500 ..

Yup there is oil in the dash pot.

Stay tuned (pun intended)

Have a great weekend

Simon up the Alps
 
Not entirely sure how to interoperate the graph you have posted, axes are rather short on labels but I assume that the X axis is needle length while the Y axis is needle diameter, correct? or is this fuel flow plotted against needle lift?

Anyway, if the pressing goal is to pass the emission test and we assume that the bottom left hand corner is tickover where you test takes place then all the needles are more or less the same.

Do you vent the crank case emissions into the induction system?

Having said all that it looks like all the needles have been normalised to 2.515 whatevers.
 
Citizen Kane said:
Not entirely sure how to interoperate the graph you have posted, axes are rather short on labels but I assume that the X axis is needle length while the Y axis is needle diameter, correct? or is this fuel flow plotted against needle lift?

Anyway, if the pressing goal is to pass the emission test and we assume that the bottom left hand corner is tickover where you test takes place then all the needles are more or less the same.

Do you vent the crank case emissions into the induction system?

Having said all that it looks like all the needles have been normalised to 2.515 whatevers.
Click to expand...

I understood that it shows fuel flow against the step and diameter of the needle.
The mechanic explained it to me like this ...tick over is at step 4 .. yes they are all the same before that step as this is the start of it opening, the curve i have now (BGB) is way too steep at this point.
Yes for the test i will have to have the crankcase venting to the breather, however when i run it with the K&N air filter i use a catch can.
The swiss MOT is a tuff one, even after getting the whole engine and box leak free they frowned at the drip from the gear lever rods last time.
As a private person bringing a vehicle to be tested here you can't go away with recommendations it's either pass or fail however if a garage take it they can get passed with a to do list that they then "stamp" as done.
In true swiss style the MOT test centre is also the police vehicle centre -- it's not at all like i remember local sussex MOT's in the 80's ...
 
Ok, so it looks like the length of the needle is divided up into 16 equal parts on the X axis and the Y is the corresponding diameter and as you say fuel flow is plotted.

I would be very surprised if you need the throttle 1/4 open to achieve tickover, more likely the needle is around step 1 to 2.
 
Agreed, the first 1/4 will be idle to pick up, the needle should have very little to do with idle as this should be on the idle screw. This first 1/4 is critical to pick up without stalling.
 
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