about the dual su's...

[Guest BadKarmaCreepin]

they won't be there for long, but sionce they are, i might as well have it running right. when i start the car in the cold, it idles at around 600 rpm. when it warms up, it idles at about 1000. is there some way to have it idle higher when cold? i remember something about a fast idle screw, but i'm not sure if that's what i'm looking for.

 

also, so i've got the mixture tuning down (i found a chart of how many counter-clockwise turns the mixture plug underneath the carb needs to be turned according to the temp outside) but i haven't quite figured out this funky round looking tool i have that has a tube with a bubble in it. somehow i'm supposed to use this, but, uhhhhh, yeah, mechanically-challenged dan is always around. any suggestions?

[fl327]

you can always drive with the choke on until it warms up.

[Guest BadKarmaCreepin]

won't driving with the choke on foul the plugs?

[fl327]

dont think so, its just like having the throttle partway open, its not a mixture control or anything i dont think

[RPMS]

That little tool you have with a round base and a clear tube is a balancing tool (or "Uni-Syn"), and you'll need to use it to make sure that the front three cylinders get the same amount of fuel as the rear three cylinders. You can tune the carbs by ear, but the tool does a better job of things.

 

You use the tool by removing your air cleaner and pressing the round part of the tool against the opening of the carburetors. Air passing through the tool will make the little red ball float up in the tube. Your goal is to make the ball float the same distance up the tube in both carbs. You do this by twiddling your idle speed screws.

 

I was going to steal a page from an MGB carb tuning website and pretend it was my work, but I'll be honest instead. They do a good job of explaining it, and it's entertaining to read as well.

SU Carb Tuning

 

When you balance the carbs, remember that it takes patience, and you'll probably have to go back and forth several times before you'll get it right. Things will go faster when you get the hang of it.

 

Enjoy.

[jimzdat]

Actually, it will tend to foul the plugs faster--on the early SU carbs, pulling the choke caused the nozzle (the part the needle slides inside of) to drop almost a 1/4 inch, in essence richening the mix--it also kicked the throttle plates open, but only if you pulled back all the way, or had the cables adjusted wrong.

 

I am assuming we are talking about the early carbs judging from the "mix screw thingy" comment above--the later carbs did not operate the same way

 

The "funky round tool with tube and bubble" is a UniSyn--you place it over the airhorn of the carb, adjust the disc in the center so that the bubble moves up to a certain point (up to you--I usually went to the halfway mark)--then you place it on the other carb (without adjusting the center disc) and adjust the second carb to match the airflow of the first

 

I'm sure someone can give better directions, I'm going off of memory here.

May want to go to a local VW shop (if you have one) and talk to the guys that work on old bugs--they run multiple carbs on those all the time, and in fact, that's where I bought my unisyn

[260ZRED]

I have two round top SU's, and my car seems to be running good. I tuned mine by the 'ear' method. (just keep turning stuff till your engine is running smooth) Is there alot of power to be gained when using the Unysen thing? Ok and one more thing: after making sure both carbs are pulling the same vaccum, how do you get the best fuel mixture? Colortune? Luck? I'm pretty new to this, but what i did was basicly turn every knob on both cars till my car ran well and sounded strong. Is there alot of power to be gained doing it the "right" way? And what would that right way be?

[Guest BadKarmaCreepin]

ok, so idle screws and uni-syn for synchronous air flow & temp vs. counter-clockwise turns chart for mixture knobs underneath the carbs. and the carbs are tuned correctly?

[260ZRED]

thanks alot for that SU's link! Some really good info there. i dont know why i havent seen it earlier!

[DAW]

You can set the fast idle speed however you want it in relation to the choke (jet dropping) function by bending the small linkage piece in that system. Get an SU manual or a factory 240Z manual for details.

 

240Z chokes can be a PITA because sometimes they stick and one carb jet may not return to where it belongs when the chokes are released, creating havoc. I decided I didn't want the jets moving once I tuned my needles to them so I did away with the choke cables and fabricated a cold-start system using small dia metal tubing which sprays a shot of fuel into the center of the intake manifold when I activate a small electric fuel pump by pushing a button on the dash. DAW

[fl327]

do the bottom adjustment last right?

i usually just do the vaccum sync unless its reallly running crappy. just sync them with the choke off until it idles where you like it, should be ok.