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tuning twin SUs
https://ausmini.com/forums/viewtopic.php?f=2&t=99790		 Page 1 of 1
Author:  p7676 [ Sat Mar 28, 2020 11:02 am ]
Post subject:  tuning twin SUs
Anyone know anyone in the Newcastle area that can tune the SUs
Allen TY
Author:  Ian_B [ Wed Apr 01, 2020 6:38 pm ]
Post subject:  Re: tuning twin SUs
Do it yourself Alan
Assuming the motor is pretty standard make sure correct needles are fitted Er on the rich one for more safety.
Check throttle shafts and carb body for wear .This is very important .Air leak =lean .Air leak makes you move jet tube / needle to Wrong place and you cannot balance them .
This is the SU carbs biggest weakness.
New shafts are available So are oversize ones (read parallel reaming) Speak to midel.
Make sure pistons slide smoothly and make a good clunk when they hit bottom after you lift them and let em drop, which says the jet tube is centered.
This also is very important .Research how to center jet tube on SU. Easy stuff.
The more the jet tube is lowered mixture gets richer EVERYWHERE.Tapered needle in a fixed hole that can be moved around and centered.
Then they made spring loaded crap !! Yours wont be !!
Screw jets tubes down equal amount both sides say a turn and a half
Get a piece of hose and put one end to your ear.
Listen to how even the sucking noise is.
At idle you need to use linkages so you can get each carb at correct throttle position without moving the other .
Have a look at linkages its easy.
Once she is off idle a bit the synchronisation dont matter much.At idle it does.
You want good idle ,,equal air sound and move those jet tubes just equal to get best mixture at idle.
Modify the motor and then you learn about the needle taper and what the spring does.
Its lots easier than old school panel work :)
Author:  Ian_B [ Wed Apr 01, 2020 7:03 pm ]
Post subject:  Re: tuning twin SUs
We used to use three of em on holden sixes I was mates with best mechanics in town and dad was a bmc guy.
The blokes with worn shafts reckoned su was crap
We had good carbs and even did a dyno run and did an old school distributor graphed at the local Tafe many moons ago.
Author:  p7676 [ Wed Apr 01, 2020 7:03 pm ]
Post subject:  Re: tuning twin SUs
thanks Ian
Author:  Ian_B [ Wed Apr 01, 2020 7:05 pm ]
Post subject:  Re: tuning twin SUs
Im at Kurri mate TV shop The only one of us left Sing out any time if i can hep.
Author:  jimb [ Fri Dec 04, 2020 4:39 pm ]
Post subject:  Re: tuning twin SUs
Ian_B wrote:
Do it yourself Alan
Assuming the motor is pretty standard make sure correct needles are fitted Er on the rich one for more safety.
Check throttle shafts and carb body for wear .This is very important .Air leak =lean .Air leak makes you move jet tube / needle to Wrong place and you cannot balance them .
This is the SU carbs biggest weakness.
New shafts are available So are oversize ones (read parallel reaming) Speak to midel.
Make sure pistons slide smoothly and make a good clunk when they hit bottom after you lift them and let em drop, which says the jet tube is centered.
This also is very important .Research how to center jet tube on SU. Easy stuff.
The more the jet tube is lowered mixture gets richer EVERYWHERE.Tapered needle in a fixed hole that can be moved around and centered.
Then they made spring loaded crap !! Yours wont be !!
Screw jets tubes down equal amount both sides say a turn and a half
Get a piece of hose and put one end to your ear.
Listen to how even the sucking noise is.
At idle you need to use linkages so you can get each carb at correct throttle position without moving the other .
Have a look at linkages its easy.
Once she is off idle a bit the synchronisation dont matter much.At idle it does.
You want good idle ,,equal air sound and move those jet tubes just equal to get best mixture at idle.
Modify the motor and then you learn about the needle taper and what the spring does.
Its lots easier than old school panel work :)
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