Jump to content


'73 Idle limiter cap help!

Dale B.

Recommended Posts

I need someone with a good running stock carb setup from a '73 to give me a hand. My idle limiter cap was removed when the previous owner had the carbs maladjusted. Could someone please tell me how many turns from seated it should be? I want to tune the carbs but There is no mention in the service manual as to where it should be set when someone has messed with it.


Link to comment
Share on other sites

  • 2 weeks later...

Those Japanese carbs drove me mental so I tore them off about 12 months after buying my Z, so I don't have actual experience, and I'm not sure what you mean by 'idle limiter cap'. (Could be an American/Australian terminology difference)

Assuming you mean the idle adjustment screw, you just turn it until you get the idle speed you are looking for.

If you mean the idle mixture screw, use 1.5 turns from seated as a start, then wind it out until the motor starts to stumble from being too rich, then wind it in 1 turn.

Don't know if this helps but good luck.

Link to comment
Share on other sites

I think your talking about the fuel mixture nut that sits right under the carb body. First let me say that to fully understand the SU you need to get a video called Just SU Carbs from ZTherepy. I have 3 screw carbs which have a knurled nut under the carb, it also has two steel nubs that jut out so you can tell how many revolutions you have made. I guess since you don't have yours that doesn't help so here goes. Seat the fuel mixture nuts all the way closed and then turn them both out three turns. Start the car and let it run until it's up to normal operating temp. Turn the fuel mixture nuts equally until you hear the engine begin to choke and then back off about a quarter turn. Once that is done you will have to flow test your carbs at idle, and then at normal driving rpm using the idle speed screw at the top of the linkage. To flow test your carbs you will need a unisyn flow meter about 30 bucks from MSA or ZTherepy. When you do this you will use the throttle adjustment screws on either side of the carb body. If three turns is too much then try two. There are many things to be considered on the SU like the position of the float in the fuel bowl for one, which if not right can cause a bunch of problems. Position of your needles, installing new grose jets and so on. Get that Video and you will be an SU expert in about two hours.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.