240z dies when choke is fully open

[Miles]

Check the throttle shafts  for leaks with the carb cleaner.  The shafts become worn allowing air to enter the carb. If the throttle shafts are sucking air you will never be able to correct the lean condition that causes the coughing and spitting in the carbs.

 

Yes you plugged the big leak, but air will find a way in from some other point.  It is still sucking air.  Did you check the connections/hose to the brake booster that come off of the intake manifold? 

 

 

Chasing air leaks is kind of  like playing wack-a-mole. Make a list of every connection and joint on the intake system and rule each one out.

 

 

Actually there is a procedure for diagnosing  engine problems. For example, before checking the intake/carbs etc you should check and set your ignition system so you know if there are problems and have the timing/dwell/plugs  etc mostly dialed in. After you correct the carb/intake problems  go back and recheck the timing/dwell etc. Otherwise you are trying to diagnose a problem while dealing with too many variables.

 

When checking for leaks with carb cleaner, did you lower the idle speed to better hear the RPMs pick up as you spray the joints, hoses, throttle shafts etc?

[5 Star Rising]

Ugh been working 11 hr days this week.. this probably why I haven't posted so much in the last 10 years lol.. time... I plan on working on the car later today or tomorrow but I like to get a good plan to jump into and start testing all the variables thanks for the info, stuff like this really helps.

 

Also question about the floats..

 

When you remove the float lids and flip them over so that the float is in front of you resting upside down. When adjusting the float level. SHOULD the weight of the float be enough to push the needle valve half closed as you are adjusting your float level?

 

Seems like the spring clip in the needle valve would be strong enough to hold the weight of the dry float up and keep the valve fully open so you can set your level. Seems like mine sags down and pushes the valve half closed in a resting position as I'm trying to adjust the float level Is this normal, or are these cheap needle valve assemblies I got making it impossible to set my proper float level? Thanks

[5 Star Rising]

So Im guessing the weight of the float is not supposed to sag down and push the needle valve half closed when holding the float assembly upside down and setting float levels.

 

Weak needle valve spring clips on new aftermarket needle valves?

[5 Star Rising]

Do you 240 guys have Anti Backfire valves on your cars. My early 71 doesn't have one, it may have been removed from the previous owner. I went and reset my float levels and I'm still getting back fire issues at all rpms after I plugged a major vacuum leak.. Wondering if I need a anti back fire valve installed. I'm going to get a new PCV valve tomorrow and try that.

[5 Star Rising]

I found the problem and it was a stupid one. Firing order was off. Prior owner had 3 and 4 plug wires on the cap switched. Car runs great now..

[seattlejester]

Hah called it. 

 

Then again I shotgunned all the potential problems.

 

Backfire through the intake can definitely point towards poor timing/spark misorder, pretty damn big fire hazard with carbs.

 

Glad you got it running right. 

Edited January 25, 2017 by seattlejester

[Miles]

From post #21 above:

 

Actually there is a procedure for diagnosing  engine problems. For example, before checking the intake/carbs etc you should check and set your ignition system so you know if there are problems and have the timing/dwell/plugs  etc mostly dialed in. After you correct the carb/intake problems  go back and recheck the timing/dwell etc. Otherwise you are trying to diagnose a problem while dealing with too many variables.

 

You learned a lot. Now on to the next problem.