I started with this adjustment guide: https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/

I can get the motor to run for a bit, but then it suddenly will stop and spit fuel back out the carbs: 

 

 

I recently disassembled the distributor, cleaned everything, put in fresh points and some other hardware. I just bought a timing gun, but it's hard to check timing on one side of the car and start it on another, seeing as how it usuall doesn't run for too long.

 

Has anyone seen something like this before?

 

Other videos: https://youtu.be/jRxGxSqsDXw, https://youtu.be/4MFxvqKeHo0

Isn't that the same video from Hybridz?  Did you do the stuff that was suggested over there?

Yes, same video. Link for context: https://forums.hybridz.org/topic/131555-help-new-to-me-240z-l28-wont-idle/?ct=1590465931

I've been having issues with the other forum, so I'm trying this one.

 

I tried disconnecting vac advance, moving distributor to adjust timing, issue still occurs. It seems like something is vigorously stopping the motor from running, but I have no idea what it could be yet.

I'm not an SU expert but I know that intake vacuum controls the position of the piston in the carb that controls the amount of fuel allowed in to the air flow.  So your problem is probably related to what happens from start to engine running.  

The piston is in one spot at start, its resting position, with zero intake vacuum then moves, or is supposed to move, as intake vacuum develops.  The new position causes the engine to spit and die, or the piston is stuck and doesn't move and this causes the engine to spit and die.

I'd focus on making sure the pistons are moving like they should, with correct oil in the damper.  Seems like you're getting a "lean" kickback, which implies that the carb pistons aren't moving, or aren't moving fast enough, which would keep the needle low in the jet making things lean.  Engine starts, goes lean, kicks and dies.

This is from my latest understanding of SU's, developed as I read your post and also pondered what little else I know about them.  The throttle blade controls the airflow, the piston position controls the fuel mixture.  The kickback sounds lean.

Hmm that is a good insight. 'kickback sounds lean'.

Today I did take the suction pistons apart and clean them, and put the correct oil in the dampers. I might look into how they might be getting stuck.

I also bought the color-tune spark plug listed in that tuning guide, but haven't tried it yet. Maybe that will give some insight as well.

Thanks!

from the image that you posted in the other forum it looks like your dizzy/dizzy pedestal  is not installed correctly. The thread hole should be on the header side of the motor, currently its on the radiator side (front).

Further it looks like your setting the dizzy far too advance, this can cause the backfiring issue you are experiencing.

Review the images here in this thread ive linked

Read the directions below, then read them again.

1. Remove the Dizzy and set your pedestal correctly (if its wrong, looks that way)..

2. Set the motor to TDC on cylinder 1 on the compression stroke.

2.a You can verify the compression stroke by using your thumb on/in the spark plug hole for cylinder 1 feeling for the air pushing out while the piston moves to the top.

2.b You can use a long metal screw driver to feel the piston at the top ( dont let it hit the piston walls ).

2.cIf you dont feel comfortable with that, take off the valve cover and get to TDC with the cam lobs on cylinder 1 facing out.

3. After you do that you need to verify that the asymmetrical cam gear is pointing in the 11oclock position.

4. reinstall the dizzy that you removed.

4.a When you reinstall the dizzy the cap should be right about to hit Cylinder 1.

Start messing with the carbs after you ensure that the timing mechanical AND electrical  / valve clearance work correctly.

 

EDIT:

Something seems strange about the pedelstal, might just be me at 1am.

There should be a screw that fit into the bottom of the dizzy on this side. https://photos.google.com/share/AF1QipMy0E9uWSgHsEd5n8MsPKqvDId_wP16YCQTysMwYCnvx1W_3OKiBFFkNoi5kllmiw?key=X0MzRExUTWlMeHFPMF9GYVlFR1AycUNaMjJ2X093

That allows you to limit the advance that you place on the engine on this side.

https://photos.google.com/share/AF1QipOKErtk-ULO01S-PEtXmxC2Y66aMcr2FzODqfCL6ZaUoGLmERZhXyEchPsBuQUbKw?key=VzVMQjR6V1A3bm1rLUtoN1VvQzgtUGgtWTEzWmpR

Try reducing the timing a bit. I want to verify the distributor settings, but i cant look at my car, i got it all tucked up for the bit of rain we are to get in the morning. Ill see if i can get pics tomorrow for ya.

Edited May 30, 20204 yr by heyitsrama

8 hours ago, heyitsrama said:

from the image that you posted in the other forum it looks like your dizzy/dizzy pedestal  is not installed correctly.

I don't think that he has checked the timing yet, or tried adjusting it.  

 

It is very close to the very first thing that is done when starting an engine that has been apart and reassembled.  Engines are all about timing.

I'm always happy to offer an alternative path for people who don't want to try the well-worn one.  He'll have to check the timing eventually.  In the meantime...carbs.

I forgot to mention earlier, I think I figured out the distributor pedestal mystery. It appears to me like the previous owner took the distributor out of an L24 engine and slapped it onto the L28 pedestal and engine. In one box of parts I found the transistor ignition box with all the wires cut. I flipped the pedestal around and tapped some new mounting holes:
https://photos.app.goo.gl/Ln9hh2FvdabMKeiP6
https://photos.app.goo.gl/PnJSctfa4Qp9UrGa8

Why the P.O. would "downgrade" to the points dizzy, I don't know. I'm looking into upgrading to a new ignition at a later point.

Another interesting tidbit: I just removed plugs #1 & #2, and it would appear that cylinder #1 is not firing, as the plug still looks brand new:
https://photos.app.goo.gl/hgHEgfVZVgqBqDwa6

As I don't currently have a good way of turning the crank by hand, I've just been trying to eyeball things :'D

I have a 27mm socket coming in the mail. The closest I have is 1" & 29mm deep, so I might just need to wait. Socket should arrive Tues.

1 hour ago, koroluka@gmail.com said:

Why the P.O. would "downgrade" to the points dizzy, I don't know. I'm looking into upgrading to a new ignition at a later point.

Another interesting tidbit: I just removed plugs #1 & #2, and it would appear that cylinder #1 is not firing, as the plug still looks brand new:

As I don't currently have a good way of turning the crank by hand, I've just been trying to eyeball things :'D

If he had a points distributor and the electronic system quit working, why not?  A spark is a spark.  Electronic can be a better spark but the first systems just made the same quality spark in a different manner.

Brand new would be bright white. Those both look like they've been in a working combustion chamber.

Sometime you can grab the belts and turn the crankshaft.  Squeeze them tight on a pulley so they grab.  If you have an extra pulley on the damper you can take a spare belt and make a handle out of it.

A timing light would answer a lot of questions for you.  But trying new workarounds is fun too.

 

Edited May 31, 20204 yr by Zed Head

Okay, I managed to get it to close to #1 TDC: https://photos.app.goo.gl/AcjWnUn1WbWCt2REA

But this is what the distributor looks like: https://photos.app.goo.gl/d11xkbEXiagMp6sdA

Something seems off here...

You might be on the exhaust stroke.  TDC happens twice per full combustion sequence.  Rotate the crankshaft one full rotation and the rotor will be on the opposite side.

 

Haha derp, okay gave it a 360deg turn and this is what it looks like now: https://photos.app.goo.gl/NnBwiLwbx2KAPU4o7, https://photos.app.goo.gl/q9gQSErUXPYjpVVz9

Thanks for the help thus far ?