[Roadsters] Carb Setup

[Keith0alan at aol.com]

In a message dated 3/24/2008 4:52:19 PM Pacific Daylight Time,  
gtpjimgammon at yahoo.com writes:

Hi

I looked, but didn't find.  

Could someone please send a link to the procedure  on setting up SU carbs on 
a 2000?

I just can't  recall how, though it has only been 30 years since the last 
time I did  it....

I have the idle setting on each carb, and an  air flow meter, but I can't 
recall how to do the higher speed mixture  setting.

JimG 1969 2k



Jim,
 
    Check the 311s.org wiki tech section. My "still not  quite done" carb 
tuning link is there now. 
 
The quick rundown is:
 
Set the idle airflow balance with the idle speed screws found down by the  
throttle shafts.
 
Using the service screw raise the engine speed to 2000 rpm. Set the high  
speed airflow balance with the screw on the bar connecting the two carbs. Lower  
the speed to idle and double check the idle balance.
 
Using the service screw again raise the engine speed back to 2000 rpm.  
Adjust the mixture knobs to achieve maximum rpm. If it starts to get too high  back 
off the service screw to 2000 rpm. To check the mixture: if you raise the  
slide a little and the engine speeds up, that carb is rich and the mixture knob  
needs to be turned in raising the nozzle. With a little practice you can push 
 the slide down a little. If the engine speeds up that carb is lean and the  
mixture knob needs to be turned out lowering the nozzle. At the correct 
setting  lowering or raising the slide will slow the engine. 
 
Lower the engine speed back to idle by backing out the service screw. At  
this point you are likely to need to readjust the idle speed. Do this with the  
idle speed screws making sure to verify that the air flow remains balanced. 
 
The idle mixture can be checked using the slide raise and lower trick. It  
should be correct. If it's not too far off call it good. If it's way rich you  
could have worn needles and nozzles. If it's rich or lean enough that you want  
to do something about it the needle can be slid out a few thousanths of an 
inch  to lean or in a few to richen. This also effects the high speed mixture 
but not  very much. The promary effect is at idle. 
 
Once you get to this point it is time to road test. If you get stumbles at  
cruise you are a little lean, riched by about 1/4 turn. Check the plugs, if  
carboned lean by about 1/4 turn. A couple tries and it should be dialed in. 
 
If you stumble when you floor it the dash pot oil is low or too thin.  
Normally use about a 10w oil, atf works fine. If that isn't thick enough  motorcycle 
fork oil works and is available in lots of weights. Once you get up  to 20w 
or higher single weight engine oil works. 
 
That should cover most of the points. Let me know if you have any  questions.
 
keith "the slow carb guy" williams



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