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

[inline6]

What distributor are you using (get the letters and numbers off of the casting)?  You need this in order to know what initial timing should be as different distributors require different settings.  Previous owner(s) could have changed it.

 

You said you've set timing many times.  What did you set it at - initial setting in BTDC (Before Top Dead Center) degrees?

 

Have you watched the timing change as you rev it up?  Are you able to see the timing advance working?  There is supposed to be both a mechanical advance (accomplished with fly weight) and a vacuum advance.  Confirm that when you rev the engine up from idle that the ignition timing changes... (it should increase).  What is the total degrees it advances to by, let's say 3500 RPM?  It should be at least in the 30 to 36 degree territory.  I understand that there may not be marks going that high.  However, you can estimate by adding some paint marks on your pulley based on the distance between the existing ones.  Paint additional marks as necessary so you can see the total advance that is occurring.

 

Have you checked that the cam timing is set properly?  Take valve cover off  (and spark plugs out) and rotate engine by hand/socket until a bright (or dark) link matches the mark on cam gear and then align cam gear to mark on front cam plate.  Be aware that there are two links on the chain that are notably different from the rest, so you may have to do this for both of them.  After many revolutions, you will see a marked link will line up with the mark on the cam gear.  When you further align the cam gear with the mark on the cam plate, you should be able to look at the timing pointer and its relation to the crank pulley markings to verify cam timing is set right.  If the pointer is not pointing at the TDC mark, then keep rotating until the next mark aligns with the cam gear mark - align cam gear with plate and check pointer at crank gear.  If neither of these line everything up, your cam timing is off.

 

Also, you should check that the distributor drive spindle is correctly installed - you can remove the distributor and view it compared to reference pics of where it is supposed to be at top dead center (look on this forum or google images).  You need to know that all of the mechanical alignments are correct before you can conclude that your ignition timing setting efforts are being accurately performed.   

 

Until you knock these things out as possibilities for the problem(s), you have too many variables to troubleshoot systematically.

Edited February 10, 2018 by inline6

[5 Star Rising]

Thanks Inline. That is some good info. I actually replaced the distributor and have the same issue. The shaft on the old distributor had a ton of play and the vacuum advance diaphragm was shot.   So I got a rebuilt unit from Autozone, the new shaft was tight and the diaphragm in the vacuum advance acually held vacuum pressure with a vacuum pump how ever the advance mechanism did not move very much even applying a bunch of pressure.

 

I cant see the engine producing as much vacuum as I pumped in that thing, so the advance probably does not work too well with the reman unit. However with the new distributor and electronic ignition excluding the points and condenser, I still have the issue. I tried the timing in mutiple positions btdc and extremly advanced and had the same issue. I wish I had a spare set of good running carbs to bolt on and see if it ran different. 

[5 Star Rising]

Here is a picture of one of the needles that was in my car. It has a "Z" on the side. The other needle on the left in the picture is out of a 72 240z that I got from a friend it was not in my carbs but just used as a reference. Does the one on the right look like a racing needle? I have no idea what to look for in comparison.

[5 Star Rising]

A few more random carb pics, incase someone sees something out of the ordinary.

[Miles]

https://www.youtube.com/watch?v=y059hdXvVwg

 

https://www.youtube.com/watch?v=SLD_7pNRfbk

 

https://www.youtube.com/watch?v=JOIFJEO7mTM

 

https://www.youtube.com/watch?v=7GRAcqDySog

 

https://www.youtube.com/watch?v=60Bj_2cZQnc

 

[inline6]

14 hours ago, 5 Star Rising said:

Thanks Inline. That is some good info. I actually replaced the distributor and have the same issue. The shaft on the old distributor had a ton of play and the vacuum advance diaphragm was shot.   So I got a rebuilt unit from Autozone, the new shaft was tight and the diaphragm in the vacuum advance acually held vacuum pressure with a vacuum pump how ever the advance mechanism did not move very much even applying a bunch of pressure.

 

I cant see the engine producing as much vacuum as I pumped in that thing, so the advance probably does not work too well with the reman unit. However with the new distributor and electronic ignition excluding the points and condenser, I still have the issue. I tried the timing in mutiple positions btdc and extremly advanced and had the same issue. I wish I had a spare set of good running carbs to bolt on and see if it ran different. 

 

Honestly, until you confirm the cam timing, and the distributor drive are installed correctly, doing other things that rely on those to be right are half efforts.  Even with the remanufactured distributor, you should get the markings on the casting so it can be properly identified.  Assumptions, such as that they sold you the right reman distributor for example, don't help solve your problem.  Facts are better.

 

You need to do what I outlined in my last post.

 

I became an expert with my 4 bolt SU carbs - I ran them for something like 15 years.  There is a list of things that need to be done right for those to be right.  However, quite a few things can be wrong on them, and they still work reasonably well.  

 

Just looking at the needles visually isn't going to help you identify them.  New old stock ones I bought for my car came with black "ink" N27 printed on the fat part of the shaft that goes inside the piston.  Easy to rub off... and once it is gone, no way to identify them by looking at them - you have to measure their diameter at specified intervals along the needles length and compare to notes others (search the internet) have made in that same regard.  You can find that info online.  The "Z" is probably just what a previous owner wrote on them with marker - no bearing on whether those are actually z car needles, or which z car needles, obviously.

 

A lot of people don't know how to set the needles in the pistons right.  And getting the needles in the correct position is a crucial thing about the Z's SU carburetors.  To start, you have to wind the nozzles all the way in, have the domes off.  Grab a piston and have the needle set screw loose enough to slide the needle in and out of the hole easily.  Then put the needles in the pistons so the fat base portion sticks out easily an 1/8th of an inch.  Next, set the set screw so it is just tight enough to keep so that the needles do not move on their own, but can move easily if pushed upon.  Test this.  The needles should move easily if you push or pull them in and out, but they should not move if you hold the piston vertically and shake it back and forth.  Set the needle again so the base is proud of the piston bottom (both the channel and the bottom of the piston). Then set the pistons in the carb bodies making sure not to bump the needles as you align them to go into the nozzles.  When you set the piston down all of the way, the ridge on the fat base of the needle will contact the nozzle - and the needle will be pushed up into the piston.  This sets a "touching" or no gap fit between the shank of the needle and the nozzle top surface.  Remove the piston carefully and tighten the needle set screw. 

 

When unscrew the nozzles to their initial settings per the manual, you will have the correct gap between the top of the nozzle and the base of the needle.   The needles are now at the correct height.  

 

Other things:

Don't bother with ATF in the piston tubes.  Just use standard 10W30 motor oil.  I tried ATF and it didn't work as well.  There are low and high markings on the screw in "dip" sticks.  Set them both to full when the sticks are threaded all the way in - don't go over.  I used a small bottle (like air tool oil) which allowed me to add single drops of oil at at time - as necessary to get the level set precisely.

 

If you don't have a carburetor synchronizer tool, buy one.  You need to get the air coming into each carb to be the same amount.  This is done at two places: at idle, and "off idle".  Until you set this correctly - the front three and back three pistons will try to operate like two different engines.  Obviously, not a good idea - not smooth.

 

With these things and those of my prior post - if you do them and can supply specifics back, maybe the solution to your problem(s) won't be far off.

 

 

 

 

 

Edited February 11, 2018 by inline6

[5 Star Rising]

Thanks Inline. I actually watched 2.5hrs of the Ztherapy SU video again last night as I had not watched it for about a year. I had written down most of the info you gave me above about the carbs and I also remember following the video and setting the needles correctly last year, what I did pick up in the video this time around was my float levels, I remember trying to set them like the video but I did not have gross jets, as I tried to set the float levels the way it shows on the video the weight of my float kept calapsing the needle valve so I was unsure if it was set correctly, I am getting a lean condition and back firing out of both carbs when the choke is off, I also have the carbs set to the richest position.

 

Before I pull my valve cover I'm going to raise my float levels a bit and see if that gets rid of the lean condition and backfire. I had only messed with the float level one time and I felt unsure at the time if they were acurate. I will try this today and see if something simple like the float level is causing this. This could actually be a separate issue that I created from the very beginning, as in earlier posts I had mentioned that I had found 2 spark plug wires swapped from the PO. It obviously made a huge difference, but I am stuck with the backfiring lean condition that I may have caused by trying to fix the first issue lol. I know.. sounds stupid. It is a possibility. I will definitely start all over if this float adjustment does not work today.

[inline6]

I just looked again at your pics.  That is not a Z on the base of the needle.  It is an N.  That was followed by the number - most likely 27.  Those are the right ones.  You really don't want to have scarring at that point of the needle.  You may want to polish them up with some 2000 grit sandpaper, or think about replacing them down the road.  Also, when assembled can you lift the pistons to the roof with your fingers, hold them tight against the roof and let go of them both really quick... and see if the pistons drop both at the same rate, and if they clunk on the carb floors.  They should drop at the same rate. 

 

And they both should clunk.  If they don't you've likely got a bent needle which can keep the pistons from seating.  That will cause a lean condition as well.  

[5 Star Rising]

I cant seem to set these floats right. Do I have the right float and hardware in here? Seems like the fuel bowls are not filling up enough, when I pull the floats out on both carbs the bowls are only like a 1/4 of the way full. Cant even see the fuel in the nozzle when looking straight down into the nozzle with a flashlight.

 

I cant seem to bend the tabs enough so the bowls will fill more with out having the float touching the lid at a steep angle, but then I run the risk of the bottom of the float hitting the side of the wall first before closing the needle valve. Any suggestions on this?

Edited February 12, 2018 by 5 Star Rising

[5 Star Rising]

[5 Star Rising]

Gonna try some washers to raise the needle valve and see if that makes a difference

[inline6]

There should only be one crush washer under the needle/seat assembly.  You're rigging if you do otherwise.  Your tab that touches the needle looks all bent - definitely wrong.  I'm going to look for a pic that shows what it should look like.

 

Take a look at these

Edited February 12, 2018 by inline6
Adding link

[HuD 91gt]

It’s been ages since I took apart my SUs. But I do believe there is two different height needle valves. If the wrong ones are in there (short in stead of tall) it could be very very difficult to set the float heights.

[inline6]

34 minutes ago, HuD 91gt said:

It’s been ages since I took apart my SUs. But I do believe there is two different height needle valves. If the wrong ones are in there (short in stead of tall) it could be very very difficult to set the float heights.

 

Maybe different for different years...  Have a look at this:

 

By the way 5 Star Rising, don't follow ZTherapy method of setting float level.  Look at the thread in this link - especially post 28.  I never had any problems setting the float levels following the factory workshop manual instructions.  No gross jets...  

 

I used the same needle and seat for both the front and the rear carburetor.  I don't recall the posts and pins holding the floats being different heights for front vs. back carb.   

 

Edited February 12, 2018 by inline6

[HuD 91gt]

Looks like that link confirmed by thoughts. Front and back are different.  Probably not your issue.

 

 

Raising the valve via washer will effectively make your mixture more lean. That’s the way it works in my head at least.

Edited February 12, 2018 by HuD 91gt

[inline6]

15 minutes ago, HuD 91gt said:

Looks like that link confirmed by thoughts. Front and back are different.  Probably not your issue.

 

Honestly, I think that guy has carb tops from different years or something.  The vents tubes, comparing between the two tops, are completely different.  My 4 screw SU's had float chamber tops that were the same.  

 

5 Star Rising - ditch the ATF.  See post 13 here.

Edited February 12, 2018 by inline6

[5 Star Rising]

Something isn't right I feel like the shorter needle valves would fit better then these tall ones thus lowering the entire setup inside the bowl. I thought I remember seeing different ones in the past as well but it's been a long time. I put two washers on each needle valve to raise it even more and I feel like I'm rigging it..

 

I finally got the fuel up close to the top of the nozzle but the float has to come up so high to the lid that it's almost sideways and bottoming out. Something is not right.. i have spent hours today trying to get the fuel in the bowl High Enough to where I can see the fuel almost flush with the top of the nozzle while having the nozzle screwed all the way in to the top. Think I may have the wrong set up in these from the beginning.

[5 Star Rising]

I have to have my float set like this to get fuel up to the top of the nozzle.

[5 Star Rising]

I have a set of each of these 3 needle valves. All pretty similar in length.

[5 Star Rising]

The ears on both my front and back lids are the same length.