36 replies to this topic

[carbon]

 

Monteemini,

 

AAU is a swing needle, there should be movement at the end of the needle.

 

Is there a brass collar with small spring attached to the blunt end of your AAU needle?

 

Without any movement the chances are the needle will foul the main jet, which is the problem you appear to be having.

 

Thanks for the info Carbon

 

There is no brass collar, it looks like it as been replaced wit a DIY turned collar that is a very snug fit to the needle.

 

is it possible to just get the brass collar? there wasn't one in any of the rebuild kits from SU.

 

OK, so looks like your needle is effectively fixed, not swing type.

 

Is your jet bearing type for fixed or swing needle? Here's a quick guide to identifying type of HS jet bearing you have fitted:

- remove jet bearing from carb body (Note: the large nut is a Whitworth size, and normally very tight)

- measure the smooth end of the jet bearing where is goes through the carb body

- then take off the adjuster nut compare thread pitch on jet bearing with a 1/4 inch UNF bolt

 

Jet bearing top diameter = 9.55mm, thread coarser than 1/4 UNF = AUC8460, coarse for fixed needles (common)

Jet bearing top diameter = 9.55mm, thread finer than 1/4 UNF = JZX2075, fine for fixed needles

 

Jet bearing top diameter = 10.42mm, thread coarser than 1/4 UNF = AUD3414, coarse for swing needles

Jet bearing top diameter = 10.42mm, thread finer than 1/4 UNF = JZX1182, fine for swing needles (common)

[Dusky]

 

Monteemini,
 
AAU is a swing needle, there should be movement at the end of the needle.
 
Is there a brass collar with small spring attached to the blunt end of your AAU needle?
 
Without any movement the chances are the needle will foul the main jet, which is the problem you appear to be having.

 
Thanks for the info Carbon
 
There is no brass collar, it looks like it as been replaced wit a DIY turned collar that is a very snug fit to the needle.
 
is it possible to just get the brass collar? there wasn't one in any of the rebuild kits from SU.
 

OK, so looks like your needle is effectively fixed, not swing type.
 
Is your jet bearing type for fixed or swing needle? Here's a quick guide to identifying type of HS jet bearing you have fitted:
- remove jet bearing from carb body (Note: the large nut is a Whitworth size, and normally very tight)
- measure the smooth end of the jet bearing where is goes through the carb body
- then take off the adjuster nut compare thread pitch on jet bearing with a 1/4 inch UNF bolt
 
Jet bearing top diameter = 9.55mm, thread coarser than 1/4 UNF = AUC8460, coarse for fixed needles (common)
Jet bearing top diameter = 9.55mm, thread finer than 1/4 UNF = JZX2075, fine for fixed needles
 
Jet bearing top diameter = 10.42mm, thread coarser than 1/4 UNF = AUD3414, coarse for swing needles
Jet bearing top diameter = 10.42mm, thread finer than 1/4 UNF = JZX1182, fine for swing needles (common)

Does not matter at all.

[carbon]

 

 

 

Monteemini,
 
AAU is a swing needle, there should be movement at the end of the needle.
 
Is there a brass collar with small spring attached to the blunt end of your AAU needle?
 
Without any movement the chances are the needle will foul the main jet, which is the problem you appear to be having.

 
Thanks for the info Carbon
 
There is no brass collar, it looks like it as been replaced wit a DIY turned collar that is a very snug fit to the needle.
 
is it possible to just get the brass collar? there wasn't one in any of the rebuild kits from SU.
 

OK, so looks like your needle is effectively fixed, not swing type.
 
Is your jet bearing type for fixed or swing needle? Here's a quick guide to identifying type of HS jet bearing you have fitted:
- remove jet bearing from carb body (Note: the large nut is a Whitworth size, and normally very tight)
- measure the smooth end of the jet bearing where is goes through the carb body
- then take off the adjuster nut compare thread pitch on jet bearing with a 1/4 inch UNF bolt
 
Jet bearing top diameter = 9.55mm, thread coarser than 1/4 UNF = AUC8460, coarse for fixed needles (common)
Jet bearing top diameter = 9.55mm, thread finer than 1/4 UNF = JZX2075, fine for fixed needles
 
Jet bearing top diameter = 10.42mm, thread coarser than 1/4 UNF = AUD3414, coarse for swing needles
Jet bearing top diameter = 10.42mm, thread finer than 1/4 UNF = JZX1182, fine for swing needles (common)

Does not matter at all.

 

What bit does not matter at all?

 

I think you'll find it might...

[Dusky]

[quote name="carbon" post="3467299" timestamp="1493406537"]

[quote name="Dusky" post="3467285" timestamp="1493404736"]

 [quote name="carbon" post="3467274" timestamp="1493402804"]
 [quote name="Monteemini" post="3467131" timestamp="1493327539"]
 [quote name="carbon" post="3467038" timestamp="1493311186"]
Monteemini,
 
 [/quote]
What bit does not matter at all?
 
I think you'll find it might...[/quote]

Enlighten me then, (no sarcasm,best expression I know in English).
I've been using all jets on both swinging and fixed needles, all depending on what the customer wanted. No problems at all. So I don't see the problem.

[Monteemini]

 

 

Monteemini,

 

AAU is a swing needle, there should be movement at the end of the needle.

 

Is there a brass collar with small spring attached to the blunt end of your AAU needle?

 

Without any movement the chances are the needle will foul the main jet, which is the problem you appear to be having.

 

Thanks for the info Carbon

 

There is no brass collar, it looks like it as been replaced wit a DIY turned collar that is a very snug fit to the needle.

 

is it possible to just get the brass collar? there wasn't one in any of the rebuild kits from SU.

 

OK, so looks like your needle is effectively fixed, not swing type.

 

Is your jet bearing type for fixed or swing needle? Here's a quick guide to identifying type of HS jet bearing you have fitted:

- remove jet bearing from carb body (Note: the large nut is a Whitworth size, and normally very tight)

- measure the smooth end of the jet bearing where is goes through the carb body

- then take off the adjuster nut compare thread pitch on jet bearing with a 1/4 inch UNF bolt

 

Jet bearing top diameter = 9.55mm, thread coarser than 1/4 UNF = AUC8460, coarse for fixed needles (common)

Jet bearing top diameter = 9.55mm, thread finer than 1/4 UNF = JZX2075, fine for fixed needles

 

Jet bearing top diameter = 10.42mm, thread coarser than 1/4 UNF = AUD3414, coarse for swing needles

Jet bearing top diameter = 10.42mm, thread finer than 1/4 UNF = JZX1182, fine for swing needles (common)

 

 

Interesting, thanks for the info carbon.

 

I have a swing type jet bearing after doing the above.

 

I'm a bit confused why the different thread size and therefore height setting of the adjusting nut resolves my problem with the fixed needle?

 

My understanding of the problem is that the needle used to be a swing type so had a small amount of play to slide in and out of the jet without drag.

Now it has been converted to a fixed needle there is such a fine tolerance with the needle/jet that it is getting stuck on its travel.

 

If the internal diameter of the jet bearing is the same on swing/fixed type then the only difference will be the number of turns on the adjusting nut, am i correct in saying this?

 

 

Am i missing something?

 

Thanks

[Dusky]

Nothing. Just center the bearing.http://sucarb.co.uk/...etter-servicing
They sell a special tool too.

[carbon]

Montemini,

 

From what you say you have the following:

- a piston converted from swing to fixed needle

- a swing type jet bearing

 

You should find that the 'swing' jet bearing is a close fit in the alloy carb body. This means that there is effectively no sideways movement in the position of the jet bearing, and any attempts to 'centre' the jet are unlikely to make any difference.

 

If you are very lucky and the jet just so happens to be in the right place for the fixed needle then it will work fine. If not then it will catch on the main jet and won't move freely.

 

So you have a couple of options:

- convert back to a swing needle

- or replace the jet bearing for 'fixed needle' type

 

Swing needles are much easier to set up than fixed, as getting the jet centred can be a right faff.

 

There's only a couple of thou clearance between the needle and inside of the main jet when jet is close up to the bridge. In my experience getting a fixed needle type jet bearing centred even using a special tool can take a while.

 

PS. This kit includes a centering tool which can be used with carb jets installed: http://www.moss-euro...s-gac6101x.html

 

With the other longer centering tool the main jet has to be removed, not a problem on the bench but a bit tricky when under the bonnet.