'71 240Z randomly started idling at 2k rpm

[austinnelson117]

Hey everybody, just for reference, my car has the earlier style SU carbs. When I first bought her I put everything back together and she ran perfectly. I adjusted the main idling screw on the top of the linkage and it idled at 700 rpm smoothly. Then, one day it just started idling between 1500 and 2k rpm. I was going to adjust the carbs but read that if the needle is the issue, leaning out the carbs can mess up the valves. I was just wondering if anyone had any suggestions where to start due to the random appearance of the problem.

Thanks,

Austin

[EScanlon]

Start by doing a "Search" here for tons of information.

Follow by buying from Ztherapy their video on the SU's.

Those two will put you hours ahead.

E

[austinnelson117]

I did a search but there was no indication from anything i read as to why it would randomly change idle speed without any adjustments

[austinnelson117]

And like I said, I didn't want to just start leaning the carbs out until idle was back to normal as one thread I read suggested that I could damage valves doing that

[Zedyone_kenobi]

Make sure the chokes have returned to fully seated. Sometimes the cable slips or you did not get them to return to the fully retracted position.

Also, check the few vacuum hoses you have to make sure there is not a leak into the system. Check the hose going to your distributor as well as the power brake booster.

[beermanpete]

Check the throttle linkage for sticking and binding.

Check the throttle opener operation (if the 71 has it).

If the idle air/fuel mixture is too rich a vacuum leak can cause high idle due to adding air and "improving" the mixture.

[Captain Obvious]

I was just wondering if anyone had any suggestions where to start due to the random appearance of the problem.

Where would I start? I would check my floor mat to make sure it isn't interfering with the gas pedal.

(They call me Captain Obvious!!)

[71Nissan240Z]

Take a water bottle and put some liquid dish soap. Dont mix the bottle up and make foam. Now spray a steam of water on every inch of your vacuum lines and see if at any moment your idle changes. Usually sudden changes in idle is due to a vacuum leak. You should eliminate this first before moving onto the carbs.