240z misses and spudders same issue thought I fixed it..

[5 Star Rising]

[Miles]

1. Download a Factory Service Manual (FSM). Should be available several places at HybridZ. It explains how to work on a Z car.

 

2. Follow the instructions in the FSM

 

http://www.nicoclub.com/archives/2-write-ups-on-tuning-su-carbs.html

 

This video is for British SU carbs, but basically the same procedure. Also, make sure that the needle moves freely in the seat as you move the float up and down.

 

 

[5 Star Rising]

Thanks miles, but I'm more concerned with if I have the correct components in these carbs to even start with. Following a manual with the incorrect parts for my carbs that someone else may have installed will get me no where.

[5 Star Rising]

Made some amazing progress today. Spent my only day off working on the SU carbs but it was worth it. So I have not test drove the car yet but I got rid of the back fire out of the carbs and also out of the tail pipe and it sound and revs up great.

 

I took your guys advice on a few things and it helped a ton thank you!!

 

First thing, the tabs on my floats were bent the wrong way, I looked up some pictures of néw floats and followed the bend in the tabs and shaped them correctly, I set the float levels correctly watching the videos you guys posted and also following my shop manual, set the firewall carb ever so slightly richer to offset the stance of the motor.

 

I cleaned the SU pistons for any grit, had a hell of a time doing a drop test on the pistons, I had bent needles and the needles also had scratches and rust at the top of the needle so the piston would not go all the way down and make that clunk sound, took the needles out and put them in my drill and pressed down on them on a rag to help straighten them, i took 800 grit sand paper and took off any burrs that were on the top of the needles.

 

 I adjusted my choke cable as it was binding on the front carb, i changed one of my nozzles as it was more centered than the one that was in there, I adjusted the jet needles by slightly tightening them and pushing them into the carb while pushing up on the nozzles and then tightening the needle set screw, this was done with the nozzles turned all the way up in the max lean position. The pistons then fell down nicely and made that clunking sound while hitting the bottom.

 

I then used 10-40 motor oil in the plungers instead of ATF.  And wow what a difference in resistance, both carb pistons went up super slow and with great resistance compared to the ATF.

 

I started the car and tuned the carbs using a Air Flow Meter and followed the ZTHERAPY notes I had written down from watching the video. 

 

My car runs soooo much better and no back fire at all. Its now getting all the fuel it needs and not running lean like before. I can only hope it drives as good as it sounds in my garage. I will have to test drive it after work one day this week. Thank you guys for the helpfull info. I knew there was something off with these SUs. Mainly the owner (myself) half assing adjustments because of limited time. Fingers crossed that she drives good under a load.

[Miles]

http://www.classiczcars.com/forums/topic/47304-1972-float-adjustment/

 

 

[5 Star Rising]

Good read Miles.

 

So I took the car for a test drive and it ran great. I believe this whole time I had 2 issues.  The plug wires being swapped wrong from the PO in the beginning of this thread. After repairing that it obviously ran wa better but I still had a miss and back fire in the motor when reving it.  

 

After this last weekend of going through the cars, I got rid of the back fire and gained clean power for once.  I know it was a carb issue because when I took it for a test drive yesterday out of the garage it ran great with no Miss but I felt like it was running a bit Rich out of the tailpipe and exhaust was in entering the cab, probably do to the series 1 hatch vents and that I have headers and a straight pipe with race muffler that is about flush with the rear bumper. I was reading some threads on this being somewhat normal for a Z.

 

Just for the heck of it I leaned out the carbs a little bit and took it back out for a test drive by doing that I got that same Miss and loss of power that I had before so then I rich and them up a little again and the car ran fine. At least now I have the floats set so that I can actually make a fine tune adjustment on the bottom of either carb as before I would screw down both carburetors as far as they would go to get maximum richness and still not make a difference. 

[Miles]

1. Better a bit too rich then too lean. 

 

2. Once the SU carb is set up and the car is running ok, leave the carbs alone.

 

3. If you plan to rebuild the carbs use quality Z Therapy rebuild kits.

[5 Star Rising]

25 minutes ago, Miles said:

1. Better a bit too rich then too lean. 

 

2. Once the SU carb is set up and the car is running ok, leave the carbs alone.

 

3. If you plan to rebuild the carbs use quality Z Therapy rebuild kits.

 

So if the car runs good but the exhaust is a bit rich that is ok?  When I come inside after working on the car, my cloths smell like I took a bath hydrocarbons. Almost as if I was standing in front of the tail pipe for an hour but I wasnt haha. Then again there is no cat converter on the car. Wonder if there is a better way to divert the exhaust from coming inside the cab. Maybe add some pipe and extend the muffler out a bit past the bumper.

[inline6]

1 hour ago, 5 Star Rising said:

After this last weekend of going through the carbs, I got rid of the back fire and gained clean power for once.  

 

Good to hear.  I'm glad we were able to help.  No ATF, use motor oil instead, pistons have to move/float freely through their entire movement range, needles and nozzles need to be in good shape (not interfering with each other at all) and installed correctly, fuel levels need to be set right.  From there, setting nozzle heights and syncing the two carbs with each other properly is about all that is left for good carb operation. 

 

2 minutes ago, 5 Star Rising said:

 

So if the car runs good but the exhaust is a bit rich that is ok?  When I come inside after working on the car, my cloths smell like I took a bath hydrocarbons. Almost as if I was standing in front of the tail pipe for an hour but I wasnt haha. Then again there is no cat converter on the car. Wonder if there is a better way to divert the exhaust from coming inside the cab. Maybe add some pipe and extend the muffler out a bit past the bumper.

 

Extend the exhaust past the rear apron, a touch past the bumper is even better.  A lot of the exhaust fumes come in around the tail light gaskets.  They do not seal the tail lights to the tail light panel 100% even when new, and if they are dry rotted, then even less so.  Pull your tail lights and have a look.  The hatch seal (main one) doesn't seal 100% either.  The curvature of the hatch panel doesn't contact the hatch seal firmly across it's entire surface (on my car at least).  You can check by getting in the hatch area and fitting a shim/piece of thick paper all the way around the opening - checking for places where you can slip it between the hatch and the seal.  Replace that seal if it is not in good shape.

 

Also, a lot of people cause the car to run rich by installing the needles to far into the piston.  You have to set the needles using the method I described.  

[Miles]

Fumes inside car have nothing to do with running rich.  Replace the hatch seal and seals around tail lights.

 

If you can find it, use an original Nissan hatch seal. The after market hatch seals don't fit well.  MSA may have original Nissan hatch seals.

[5 Star Rising]

5 hours ago, inline6 said:

Also, a lot of people cause the car to run rich by installing the needles to far into the piston.  You have to set the needles using the method I described.  

Yes i set the needles like you had mentioned. And also how the Ztherapy video mentioned.

[5 Star Rising]

What about the vented rectangle panel that mounts to the inside of the hatch, can those bring in fumes as well? I have a series 1 car but I put a series 2 closed panel on the hatch because that's all I had, I was going change it out later to the original vented panel but now I'm wondering If non vented panel might keep more fumes out. And what the heck is the purpose of the hatch vent system? Obviously it was put there for a purpose.

[5 Star Rising]

I forgot to mention, when I test drove the car yesterday I only noticed the popping/miss at a high RPM pull..this was after leaning out the carbs.

 

I took the car back home and richened them about a half turn each, then went on another test drive and the high RPM popping/miss went away. Definitely the fumes are rich but it seemed to run better that way. And I got to tell you, this little car sounds amazing. Has that throaty racing sound with this exhaust system. 

[jsteg]

It's always great to hear that another Z is running well. I agree the sound is amazing when its running well and at high RPM. I race my car and the sound is awesome when you hear it bouncing off a wall as you pass by. As mentioned before, these carbs on a Z run better if set slightly rich. The plugs have the right color and engine is happy this way. Good write up for someone in the future. Lots of good pics.