Ozdat Home Feature Cars Ozdat Classifieds Event Calander Links Trade Link Tech Resource Merchandise Donate Web Mail
It is currently Fri Mar 29, 2024 10:55 pm

All times are UTC+11:00




Post new topic  Reply to topic  [ 14 posts ] 
Author Message
 Post subject: Who can tune sus in ACT?
PostPosted: Wed Apr 06, 2011 4:44 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
pretty much need to get my sus tuned, i was wondering if anyone has the tools and know how to balance and tune them, or knows of a shop or person that can do it for me.
cheers

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego


Top
   
PostPosted: Fri Apr 08, 2011 4:21 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
Anyone?

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego


Top
   
PostPosted: Fri Apr 08, 2011 10:57 pm 
Offline
User avatar

Joined: Fri Jul 16, 2004 11:46 pm
Posts: 399
Location: 3910 Another Peninsula Boy
Its simple to tune twin SU's - Balance the butterflys and set the idle mixtures, its that easy.

Step 1. Balance the butterflys at idle.
Loosen the butterfly linkage adjustment between both carbs and start the engine without the air cleaner cover.
Using a short piece of hose or flexible tubing, put one end to your ear and put the other end in each carb whilst the engine is idling.
Adjust the butterfly adjustment (idle) screws on each carb until their suction sounds match (butterflys are balanced).
Screw in or out each idle adjustment screw in equal amounts to get the engine idling at 750rpm.
Recheck the suction sound. "Fine tune" each idle screw to get them sounding (sucking) the same.
Rebalance the idle screws if rpm is changed.
When you are happy that both butterfly's suction sounds the same at the idle speed of 750rpm approx, turn off the engine.

Step 2 Set the idle speed fuel mixture.

Locate the mixture adjusters. They are a large, round, knurled, and horizontally positioned under the carby base below each needle. Later type SUs have a position locking arm that needs to be held away from the mixture adjustment nut as you turn it.

Screw each mixture adjuster until each is positioned fully "up". The adjuster wont turn any further. This lifts a brass tube inside the adjuster surrounding the mixture needle to its highest position, which is its leanest setting. Now, screw each mixture adjuster down two full turns. This richens the mixture setting by lowering the mixture tube down the needle.

Start the engine

At this point you may have to go back to step 1 and reset the idle speed and rebalance the butterflys (using the hose suction tester), as the new mixture settings could be leaner or richer than they were before.

With the engine back at 750 RPM, locate the small piston lifter shaft protruding under the base of each carby bell chamber. Push each upward in turn, not together. This pushes up the piston in the bell chamber and the mixture needle attached. If the mixture setting is right in this carb, the engine speed will increase momentarily, then return to normal idle speed. If the speed stays up, the mixture is too rich. Release the lift shaft and then adjust the mixture screw underneath the carb up by a quarter of a turn. Repeat the piston lifting process for this carb. If the engine speed stays up after the next lift, repeat the mixture setting adjustment by taking it up a further quarter turn. Repeat until the engine speed just increases then settles back to its idle speed.

If the engine dies when the piston is lifted it's too lean and the mixture screw needs to be lowered (anticlockwise turn) by similar quarter turns until the desired engine response is achieved. If you find you are lowering the mixture tube by more than three turns and getting no change, you probably have an air leak downstream (see "problems" below)

When you are satisfied each carb's idle mixture setting is correct, you may have to go back to step 1 and reset the butterflys to get the correct idle speed as the engine is now getting the right fuel mix at idle.

Step 3 Reassemble

Adjust the butterfly linkage screw between the two carbs, so both carb's butterflys start to open exactly together. This is important to ensure all cylinders are getting the same mixture for maximum power.

Check the oil levels in the piston dampers are covering the dampers, to ensure the pistons rise at the correct rate under throttle load (High suction).

Reconnect the accelerator linkage and fit the aircleaner.

Job done.

My son has twin SU's on his Datsun 1600 (L18) daily driver. He learnt to tune them in one session 10 years ago. Its done a squllion k's on two engines and the only SU carbs problem - two sunk floats due to cause noted above. It always starts easily cold or hot, idles smoothly at 700rpm and it pulls hard to 6000rpm.

_________________
RichardC
SSS016


Top
   
PostPosted: Sat Apr 09, 2011 3:12 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
thanks mate i think i can handle that, but just to be sure can you label the listed parts so i can be sure to get it right :oops:
here are some pics


Attachments:
File comment: im guessing that 2 of these do butterflys and 2 do idle mix?
[ attachment ]
101_0128 shrunk.jpg [ 169.25 KiB | Viewed 5772 times ]
[ attachment ]
101_0126 shrunk.jpg [ 123.52 KiB | Viewed 5772 times ]
[ attachment ]
101_0124 shrunk.jpg [ 172.61 KiB | Viewed 5772 times ]

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego
Top
   
PostPosted: Sat Apr 09, 2011 10:18 pm 
Offline
User avatar

Joined: Fri Jul 16, 2004 11:46 pm
Posts: 399
Location: 3910 Another Peninsula Boy
OK
You have a set of SU's from a 180BSSS of late 1974/5 vintage with flat top bell chambers. No basic differences, except there is a bit of anti pollution tubing to work around. Make sure there are no vacuum leaks around these tubes before you start tuning. I note you have no choke cables attached and the carb linkages look nice and clean? This is good practice, as dirt in the works can reduce the movement of your linkages as you try to adjust them, and you get dirty doing it!

Pic1
The single screw at the top is the adjustment for the accelerator linkage to the accelerator pedal, the first adjustment you loosen and the last you reset. This is the one that you adjust to get both butterfly shafts opening at the same moment.

The twin screws below are the individual butterfly adjusters for each carb. These are the ones you adjust up or down to get the butterflys equally balanced, using the suction hose in your ear with the engine running to listen the suction sound in each carb. Leave those butterfly return springs to the heat shield (pic 3) attached as they ensure the butterflys are seated held firmly on their adjustment screws as you adjust them. (The butterfly adjustment screws are the ones at the opposite end of the levers these springs are attached to).

Pic 2
This is the carb mixture adjustment screw. Turn it fully up, then back it down two turns as a basic starting point for mixture adjustment. That "springy metal thing" that locks into notches around its perimeter is the locking device I was trying to explain. It holds the setting when you have it correctly adjusted.

One extra point. While the mixture screw is turned fully up, push upward on the black plastic fuel feed pipe below it. The mixture tube is designed so can be pulled down manually by the choke lever against that big spring wrapped around the mixture tube. This richens the mixture for cold starts. The mixture tube should return to its fully upward position when the choke is pushed off, but with years of use, or non use, the mixture tube can get a bit "sticky" and the spring may not fully return the mixture tube up to its correct position. Just worth checking it moves down against the spring, and springs fully up without restriction, before starting on the mixture adjustment settings.

I can not see the little pin used to lift the pistons in the bell chambers when you want to check your mixture settings. Can you find these? They are small metal pins about 2mm in diameter, protruding about 12mm downward under the bell chambers. When you pull your finger off them you should hear the pistons in the bell chambers click softly as they hit the floor of the bell chamber.

Hope this helps. I will check again to see if you have any more questions. Good tuning!

_________________
RichardC
SSS016


Top
   
PostPosted: Sun Apr 10, 2011 12:56 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
Yeah i know the little pins thanks heaps for that info, i have found that the only way i can get the engine to run at the moment is to have the mixture tube pulled down by the choke and wire them in place, it runs horribly. im scared to start messing with it out of fear that it wont run again. currently i can drive it so i can take it somewhere to be safe, but i would like to know wether you think id be able to get it running if i did these steps.

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego


Top
   
PostPosted: Mon Apr 11, 2011 9:51 am 
Offline
User avatar

Joined: Wed May 28, 2008 3:01 pm
Posts: 57
Location: Canberra
jakes performance 62554545

_________________
FIVETEN-orange 1969 datsun 510
YLD.510-purple 1969 datsun 510


Top
   
PostPosted: Mon Apr 11, 2011 1:35 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
thanks aaron i have spoke to jake and he said for the sus i should see dynotune braddon as they will have more parts, i dont really want to go to a shop untill i know i cant fix it :D

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego


Top
   
PostPosted: Thu Apr 14, 2011 2:40 pm 
Offline
User avatar

Joined: Fri Oct 22, 2004 7:49 pm
Posts: 150
Location: Canberra
hey mate, I can tune SUs if you need. I ran them for years, may be a little rusty but I'll happily give it a shot.

_________________
'...to 180B or not to 180B, that is the question...'

The Datto...
'74 610 180B
SR20DET on 18psi and E85. 220kW.


Top
   
PostPosted: Thu Apr 14, 2011 6:27 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
that would be awesome, i have your number so ill send you a txt so you can let me know when your free

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego


Top
   
PostPosted: Thu Apr 14, 2011 6:33 pm 
Offline

Joined: Sat Nov 06, 2004 8:17 pm
Posts: 916
Location: Western Australia
thats some great indepth information there richard. I vote Mods transfer this into the tutorials section after itdato damo has got his info

_________________
Circuit Race 1600 in the build


Top
   
PostPosted: Thu Apr 14, 2011 7:04 pm 
Offline
User avatar

Joined: Sun Mar 08, 2009 2:22 pm
Posts: 94
Location: Canberra
im happy for it to be transfered i found it to be very helpful

_________________
1972 datsun 1600 white: parts car now
1970 datsun 1600 light green(ish) alive and kicking.... with rego


Top
   
PostPosted: Thu Apr 14, 2011 11:37 pm 
Offline
User avatar

Joined: Fri Jul 16, 2004 11:46 pm
Posts: 399
Location: 3910 Another Peninsula Boy
A couple of additional points.

I should have referred to the Datsun carbs as Hitachi manufactured copies of the SU design. If you were to order parts you would need to specify them as Hitachi's, but for tuning purposes, they are identical to SU's.

Below are additional tips if you have difficulty getting the mixture settings correct on a stock or mildly ported engine with a mild cam profile. I thought I had sent this in my previous post, but it got lost in editing.

If an overly rich mixture setting is required:

If you have to adjust the SU mixture settings over three turns out (anticlockwise looking from the top of the carb), this is a rich setting. This indicates there possibly is an air leak downstream of the fuel jet.

Some potential causes:

Excessively worn butterfly spindles letting air past their bushes. (Temporary fix to test is to coat spindles externally with thick grease) Permanent fix is to replace these bushes and/or replace spindles.

Air leak through cracked or poorly fitting rubber hoses. Distributor vacuum hose or anti pollution plumbing.

Air leak through the gaskets at carby or engine end of the inlet manifold. (First check all nuts for tension, next check gaskets for failure) The carb end gaskets can be easily fabricated from a suitable gasket paper or repaired with gasket paste/silicon. Manifold gasket failure - fit a new one.

If an overly lean mixture setting is required:

If the mixture screw needs to leaned off excessively (up one and a half plus turns from the initial "two turns down" position) it suggests too much fuel is flowing into the venturi.

Check the fuel level in the fuel bowls. You set the fuel level in these carbs by adjusting (bending) the fork above the float that connects it to the needle and seat. The fuel level is supposed to be 12mm - 15mm? (from memory) below the top of the fuel bowl (with the float in it). The surface hight of fuel in the fuel bowl should approximately equal the hight of the top of the mixture tube that surrounds the needle in the venturi. If the fuel hight in the fuel bowl is too high, you will see fuel flowing by gravity from the fuel bowl into the inlet manifold, rather than being sucked in by the difference between air pressure outside and inside the inlet manifold.

Another possible cause (unlikely) is an excessively enlarged orifice in the mixture tube and/or the mixture needle is worn or incorrectly seated in its piston. Replace the worn parts, or readjust the needle position. The needle's thicker base should be flush with the bottom of the piston. Take care not to bend the needle.

_________________
RichardC
SSS016


Top
   
PostPosted: Fri Apr 15, 2011 2:09 pm 
Offline
User avatar

Joined: Fri Jul 16, 2004 11:46 pm
Posts: 399
Location: 3910 Another Peninsula Boy
Correction to depth of fuel in fuel bowls. Its 22mm - 24 mm below the top of the bowl.
For those who want more details have a look at this great site.

http://www.jetlink.net/~okayfine/su/sumain.html

_________________
RichardC
SSS016


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 14 posts ] 

All times are UTC+11:00


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to: 

Powered by phpBB® Forum Software © phpBB Limited