240Z dies out when choke is fully open.

[5 Star Rising]

 

I have a 12/70 71 240z that i bought recently that runs like crap. I do not know the past history of the car or the past owners so I'm starting with a running car that runs, but not great. I have been replacing old parts these last few weeks and in the middle of a tune up. 

Removed funky electric fuel pump and switched back to a mechanical pump, new fuel filters,new spark plugs and wires, ign cap and rotor, I have not yet done a compression test on the motor. I have fuel going to the carbs and can start the car by pulling the manual choke when cold like normal, but after the car warms up and I open the choke fully the car starts to idle rough and dies out almost like it's getting too much fuel. 

When I have the car running best is when the choke is slightly pulled back about a quarter of the way. When you Rev up the motor there is a slight spudder or miss through out the rpm ban. Just feels like the carbs are out of tune or not adjusted right. The car lacks that snappy throttle response, and still has a slight miss. I was getting ready to pull the carbs and get a rebuild kit for them but thought I would post this first, I have not rebuild SU's before and may be over looking a few things, like a proper adjustment while on the car. 

I found a few rebuild threads on here that I will follow, but I'm wondering why the fully open choke kills the motor and what may cause that. 

[Mark Maras]

Judging from your description of the problem, the engine is running lean when the choke is off. Giving the engine choke is richening the mixture. 

 Places to start. Finish the complete tune up including adjusting the valves. Make sure the rotor is in the right position when the engine is on TDC, top of power stroke, check and or adjust the float levels in the float chambers and lube the outside of the jet nozzles. Start it up and tune the carbs. You could also throw a compression test in there too. These basic procedures will usually fix most poor running engine problems but if they don't fix it, you'll narrow down the options of what else might be wrong.

[5 Star Rising]

Yes I will be doing the rest of the tune up this week. Checking TDC and such.  I have not worked too much on SU's. Can checking and or adjusting the float levels in the float chambers and lubing the outside of the jet nozzles be done while the carbs are still in the car? O'Reillys has a so called "rebuild kit" for this car in stock locally for a pretty in expensive price. Not exactly sure what comes with it or if its worth getting.

[Mark Maras]

 The carbs don't have to be removed. Do you have a manual (Nissan, Clymer, Haynes, etc? that deals with SUs? Any that I've seen have good information for noob's about caring and tuning SU's. BTW, these SU's are the simplest, easiest, most dependable carbs I've ever used and worked on. I was amazed at the simplicity the first time I worked on them. I would recommend getting a copy of the DVD "Just Su's" from ZTherapy. It goes into detail about them but for now a basic SU tuneup manual should be all you need. If you have any questions in the process, just ask.