Joined: Jan 2022 Posts: 76 Threads: 19
Reputation:
0
Location: cambridge
Car type: A7 special 34
Having finally got the new engine in our car and had it running it appears to be running a tad rich and was wondering what the best jet needle is for a 1 1/4" SU HS2 of moggy minor and mini era the current one seems to be marked OH or OF its a bit difficult to see as the marking is a bit scuffed. Engine is big valves, trials cam slipper pistons currently using a 37 H/C head. Possibly off to the rolling road in the new year when its run in to see what it will do as I am keen to see having bored and ported the block in the bridgeport and undertaken much of the work in our little machine shop.
Joined: Mar 2015 Posts: 5,460 Threads: 231
Reputation:
67
Location: Scotchland
Yesterday, 10:50 AM
(This post was last modified: Yesterday, 11:24 AM by Ruairidh Dunford.)
When you go to rolling road, ask them to advise you.
I have discovered over the years that generalised advice on SU set up for individual engines is very hit and miss, it may get you near but a rolling road will get it correct.
Joined: Aug 2017 Posts: 3,413 Threads: 107
Reputation:
28
Location: Darkest Bedfordshire
FWIW I run an AN in my very mildly tuned Ulster rep with an HS2.
It runs OK & would certainly do as a starting point.
I've never made a serious attempt to optimise it (there was always something else to do!) but by observation it's a little richer pottering at low rpm than on a high speed run.
(Do you know of an A7-friendly rolling road facility in the Cambridge area? I might be tempted some day...)
Joined: Aug 2020 Posts: 23 Threads: 3
Reputation:
0
FWIW the last time I had to get a SU set up on a rolling road, with a SU specialist, he started with a weak needle and tuned it in by filing a flat along one side progressively working from idle. He got an ideal result and I never had any mixture problems thereafter. This was done after he had set up the piston to rise to near maximum at max depression. This can be done either by adjusting piston weight or spring strength if carb has one.
Joined: Jun 2019 Posts: 17 Threads: 2
Reputation:
0
Location: NZ
Car type: 1933 Austin 10/4
Burlen Fuel seem to list two types of AN jet Needles.
.090 and .100 for the same AN type.
Can anyone advise what the difference is?
And what is this dimension or reference number referring to... needle thickness maybe?
My SU reference manual makes no statement about this that I can find.
regards
Gary
Joined: Nov 2017 Posts: 9 Threads: 0
Reputation:
0
Location: Scottish Borders
Gary,
Having just had a look at my SU Reference Catalogue I think the measurements you are querying refer to the Jet sizes. There is in fact a third size - 0.125"
Joined: Jun 2019 Posts: 17 Threads: 2
Reputation:
0
Location: NZ
Car type: 1933 Austin 10/4
3 hours ago
(This post was last modified: 3 hours ago by GaryCullen.)
Thanks Neil,
So a needle with 0.090 is related to the main jet size of .090?
If so then I didn’t know this relation ship between needle and jet size existed!
and if I have an mis match then may explain the hesitation in accelerating unless the choke is out a bit to make it richer.
I will be checking…
Gary
My next question is: for an A7 running an HS2 what main jet size is used?
Gary
