I can't get my SU carbs tuned right.

[Guest Anonymous]

So the thing is these SU carbs just wont tune right. They are "in sync" But they are dumping masive amounts of fuel into the car so that it tries to flood itself out, especially on a take off/ i.e. going from a stop. What should I do?

Charles

[Lockjaw]

More info needed. Does it idle fine?

 

I would start with the basics. Check your fuel pressure, float levels, and then adjust the needles per Z therapy specs. esentially turn all the way in and back out 2.5 turns, and adjust for fastest idle from there.

 

You could also make sure you have springs and fluid in the pistons.

 

See if you can get Norms attention too, he is likely the best source of SU info.

[Guest Anonymous]

It idles just fine. Its a 72 240z.

By needles do you mean the ones going from the very bottom of the carb upward to the cylender? 2.5 turns on those? Man the Haynes manuel I have says to do .5 or 1 full turn. I'll try that. Thanks for you help.

[ianz]

The 72 carbs have a different needle valve mixture screw than the earlier SUs do, so disregard the 2.5 turns thing

 

There are MANY writeups on tuning SUs, all similar, but still different.

 

do a couple of checks before you go any further.

 

Remove your air filter(s)

 

1. check the oil in the tops of both carbs, and makes sure the lift can (the sliding assembly that the Needle is attached too) in both carbs has resistance when raised by hand and fall easily with a pronounced "clunk"

 

2. also make shure that your nozzles are seated up against the bottom of the carbs (Actuate your choke and you'll see the nozzles moving in and out of the bottom of the carbs.

 

3. Buy the Z therapy Video......

[260ZRED]

ok heres how i tune mine.. may not be the best method but it works.

 

first of all you need to find your fuel mixture adjustment knob. should be a little wheel with grooves, on the very bottom of the carb. imagine it as a screw: when you turn it all the way out it makes that one carb run richer. when you turn it all the way in (to the left, counter clockwise) the carb will run leaner.

 

let the car warm up

take off the air cleaner

disable the choke mechanisms (or just make sure they're not stuck or in the way)

turn off the engine

now turn both mixture adjustment wheels on all the way toward LEAN (turn counter clockwise)

when you're sure they can't go any more, turn both of them about 2 and a half turns toward the richer side (clockwise)

start the engine

adjust the airflow of each carb so it matches the other

(get a unisyn tool or just do it by feel)

 

ok now heres the tricky part and where everybody will have their own favorite way of doing it:

 

what i do is set the revs to about 1000 and slowly and evenly start making the car richer (turn both knobs evenly clockwise, keep track of turns)

you should hear the engine run better, and the rpms will rise

lower the rpms back to 900-1000 throught the airflow, keep measuring to make sure its even

rev the engine periodically to annoy the neighbors

eventually you will find a point where richening the mixture will no longer provide an increase in RPMs.

go just a tad towards the lean

throttle response should now be instant and crisp

 

 

set your idle to about 800 and go for a ride. should feel like a whole new car

 

also, an important thing to check for is the dampner oil levels (i refilled mine with tranny fluid and its working great)

 

let us know how it goes.

[Lockjaw]

If he gets the Z therapy video, it will tell him to do the 2.5 turns thing.

 

Just thought I would point that out.

[ianz]

I believe there is a stop tab on some of the SU carbs with the detent dial mixture adjustment that wont let you turn it more than about a turn, but I am not as familiar with that type so I may have mispoken......

 

No affense lockjaw!! 8)

 

So I repeat....buy the video