240z Timing Struggles

[KiileZ]

Hello! I don't post here much, mostly just try my best to find the information I need since it's all been posted at one point or another. After doing my research I still can't find the answer to my current dilemma. 

Background: I have a 72 240z. It's got the original L24 in it with a few simple mods. A cheap exhaust header, electric fuel pump and electronic ignition. I have been slowly cleaning things up and replacing some old and worn parts. I rebuilt my SU carbs last year and when I went to tune them I had some issues with the color tune. Ended up just doing by checking plugs and adjusting. One thing I never messed with was my timing. It always seemed to run pretty good and I just never checked it. I recently did a valves adjustment and just so happened to notice my distributor was set to the fully retarded position. I figured I might need to adjust my carbs since I did the valves and figured I should set the timing up first since that was probably why I struggled to get a good mixture. So that's what I did.

My dilemma: I pulled out my old snap-on adjustable timing light and set it to zero and fired the engine up and pointed it at the crank pulley. Didn't see any timing marks at all. I shut the car off rotated the motor until I found them and marked them with a pen. Fired it up again and checked the marks. I noticed the car is running way advanced. Like 70-80 degrees advanced. If I adjust the distributor any more it dies or runs terribly. I read that it could be my balancer is bad so I set my engine to TDC and all of the marks line up. The balancer is on the zero mark at TDC as well as the cam. I did notice the shaft that runs my distributor seemed to be more towards 12 than 11:30 so I pulled the oil pump and moved it one tooth. Now it's worse. My plug wires are correct. The rotor on my distributor looks right. Everything mechanically seems correct, but I have no idea where the timing is. 

My thoughts: I think it could be a bad balancer maybe, but the marks line up when I am at TDC. I also have an electronic ignition instead of points so it's possible the sensor in the distributor is set incorrectly. I also thought maybe my vacuum advance is not working correctly. 

Any advice at all would be great. The car used to run pretty good until I decided to fiddle with the timing.

[Zed Head]

When you have the timing marks lined up on the damper at TDC compression stroke pull the distributor cap off and see where the rotor is pointing.  That will be your "true"  number 1 cylinder.  Might be that your oil pump shaft is off and somebody moved your wires to compensate.

[KiileZ]

2 minutes ago, Zed Head said:

When you have the timing marks lined up on the damper at TDC compression stroke pull the distributor cap off and see where the rotor is pointing.  That will be your "true"  number 1 cylinder.  Might be that your oil pump shaft is off and somebody moved your wires to compensate.

I replaced the plug wires. The cap can only go on one way and the cap marks where the number 1 plug wire goes. I thought the exact same thing you did and tried to move all the plug wires one spot, but then the car wouldn't run.

[Zed Head]

My point was that #1 is wherever the rotor is pointing when the marks are lined up.   The spark will jump to that electrode in the cap when the coil discharges.  If you wanted to and didn't have the screw on the adjustment limiting you you could make any cylinder you want #1, as far as spark is concerned. 

The mark on the cap is for when everything like it's supposed to be.

The engine will run fine even when things are off.  Check that rotor position.  It's the most important thing.

Or, you could put your timing gun on other plug wires until you find the one that is right.

Edited June 8, 2020 by Zed Head

[KiileZ]

8 minutes ago, Zed Head said:

My point was that #1 is wherever the rotor is pointing when the marks are lined up.   The spark will jump to that electrode in the cap when the coil discharges.  If you wanted to and didn't have the screw on the adjustment limiting you you could make any cylinder you want #1, as far as spark is concerned. 

The mark on the cap is for when everything like it's supposed to be.

The engine will run fine even when things are off.  Check that rotor position.  It's the most important thing.

Or, you could put your timing gun on other plug wires until you find the one that is right.

Olay, I think I understand what you are saying. So I have checked the rotor and when at TDC it is a good bit past (CCW) of the #1 electrode. Which is why I chose to move the distributor shaft a tooth. It sounds like I need to move the distributor shaft more in order to get the rotor to line up better with the #1 electrode. I based the shaft position off of a thread I read where it said the position should almost be pointing at the bolt hole at about 11:30, but if that causes my rotor to be in the wrong position then I need to move it until it is positioned where I expect it to be.

[7tooZ]

What did you mean when you said “electronic Ignition “. What is it and did you install it?

[KiileZ]

4 minutes ago, 7tooZ said:

What did you mean when you said “electronic Ignition “. What is it and did you install it?

I did not install it. It replaced the points. It's an xr-3000 by Crane. There is an ignition box, coil and then an optical sensor and shutter in the distributor.

[Zed Head]

While you're studying the problem, just remember that every time the shutter passes the sensor a spark is generated.  So wherever the rotor is pointed will get that spark.  

The plug wire numbering is somewhat arbitrary.  Some engines have number 1 at the back.  V8's can have #1 on the left bank or the right bank.  p

A crank damper could have six marks on it, one for each cylinder.  That would make life easier for everybody.  The timing light would always have a reference mark.

[KiileZ]

3 minutes ago, Zed Head said:

While you're studying the problem, just remember that every time the shutter passes the sensor a spark is generated.  So wherever the rotor is pointed will get that spark.  

The plug wire numbering is somewhat arbitrary.  Some engines have number 1 at the back.  V8's can have #1 on the left bank or the right bank.  p

A crank damper could have six marks on it, one for each cylinder.  That would make life easier for everybody.  The timing light would always have a reference mark.

Right, so I think my plan is going to be readjust the rotor so that it is pointing where the #1 electrode is at TDC and then resetting the optical sensor in the distributor so that it is over one of the gaps in the shutter.

When at TDC should the rotor be point directly at the electrode for #1 or should it past or before it?

[Zed Head]

Set your distributor rotation adjustment to where you can get lots of advance if you need it.  Put the screw in the slot so that you can turn the distributor clockwise with lots of space in front of the screw and just a small amount behind.  Then set the slot in the shutter right about on the money.  The leading edge is probably the trigger.  Then you'll be right around zero when you start the engine and can turn the distributor to get the 8 - 15 degrees that you'll want.  

Edited June 8, 2020 by Zed Head

[Mark Maras]

The rotor should point directly at #1 when at TDC.

[7tooZ]

3 hours ago, KiileZ said:

I did not install it. It replaced the points. It's an xr-3000 by Crane. There is an ignition box, coil and then an optical sensor and shutter in the distributor.

You should have a red light on the black box that tells you when the charge is sent. This greatly affect your timing. I recommend that you get the engine to TDC. Make sure you check it to make sure you have the piston right. Hopefully the timing Mark is now at zero. then make sure the rotor at the number one wire. Everything should be ready. Then move the crane pick until it lights. Now rotate the engine one more time to make sure the light comes on  just as the rotor is coming on the number 1. Here is a link to the directions. 
https://static.summitracing.com/global/images/instructions/xr700 instructions.pdf

On mine I start at 7 degree BTDC and adjust from there checking vacuum advance and idle. Adjust the valve, check the plug gap and then on the the carbs. good luck. I cane provide photos if needed