Slight miss in my 69 Z28

[Mr.Nickey Nova]

Did you install a standard point set or a HI-PERF set?? You should have a stiff spring HI-PERF set of points so there is less chance of point bounce at higher RPM's. Too much point bounce means loss of power...

[earntaz]

Yep [img]<<GRAEMLIN_URL>>/scholar.gif[/img] Also, what is total timing now? Too much will cause the engine to lay down at high RPM. Timing should be all in around 3K RPM ... 36 - 38 degrees as a good starting point. Other experts should chime in on this. TAZ

[sixt9rsx33]

It is a hi performance set of points. The total timing is 37*. Thanks guys

[DW31S]

That should be an easy thing to diagnose and yet, will make you pull out your hair. How about fuel volume and pressure? Fuel filter? Do you have access to a known good distributor? Have you checked all grounds? Engine ground to chassis? One cylinder not firing exactly perfect would cause the eradic idle, but engine should still rev over 4500. Gotta get back to basics and try one change at a time. Dwell 28-32 (or pop in electronic to rule out dist.) timing all in by 3000rpm and 36 degrees for street should be good. Fuel pressure around 7 should be good. Could be a minute crack/cracks in cap and cross firing inside and invisible to the naked eye. Dead valve springs will cause same symptoms, as will valves out of adjustment.

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DW31S</div><div class="ubbcode-body">That should be an easy thing to diagnose and yet, will make you pull out your hair. How about fuel volume and pressure? Fuel filter? Do you have access to a known good distributor? Have you checked all grounds? Engine ground to chassis? One cylinder not firing exactly perfect would cause the eradic idle, but engine should still rev over 4500. Gotta get back to basics and try one change at a time. Dwell 28-32 (or pop in electronic to rule out dist.) timing all in by 3000rpm and 36 degrees for street should be good. Fuel pressure around 7 should be good. Could be a minute crack/cracks in cap and cross firing inside and invisible to the naked eye. Dead valve springs will cause same symptoms, as will valves out of adjustment. </div></div>

These are all good things to check. When the car had the choppy idle I changed out the points and the car would not fire at all. I fiddled around with the wires on the distributor and got the car to start then when I set the dwell, I got a spark when i put the screwdriver in to adjust the points. I think I must have a distributor wiring problem? Going to start with that and then work forward. One thing to keep in mind...when the idle was choppy/missing it would pull hard to 6K plus...ugh...crazy...will keep playing with it. thanks for the help

[earntaz]

Don't know if this has been mentioned yet -- check for side to side play in the distributor shaft. Excessive movement ... you will never get a good dwell angle. TAZ

[TDW]

When you changed the points, did you also change the condenser? I have had quite a few brand new condensers bad out of the box lately for HD motorcycles.

[napa68]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TDW</div><div class="ubbcode-body">When you changed the points, did you also change the condenser? I have had quite a few brand new condensers bad out of the box lately for HD motorcycles. </div></div>

THIS^^^^^^^^^^

I had it in my 62 as well

[napa68]

I have observed a few things in this thread

1. The issue seems to revolve around the distributor. It certainly sounds as though the ground wire to the contact plate is compromised. Excessive shaft clearance could very well be an issue as you approach higher RPM. As mentioned, try a known good distributor.

2. Is the issue in anyway related to engine temp? As mentioned, you could have a coil on the way out. I recently had this on a T.I. LT-1 I used to own.

3. Has the voltage at the positive terminal on the coil been checked both at both cold and warm engine temp? If the harness is original, you are dealing with something 47 years old. Even corrosion at the harness bulkhead can reduce primary ignition voltage (prior to the resistance wire) that would induce a drivability problem.

Sorry if this has been covered somewhere in the thread and I missed it. Don't overthink the problem. Start with the basics.

Once you do determine what your miss truly is, I would not hesitate to send the dizzy out to someone like Jerry M. for an overhaul. I think you would be impressed with the difference!

Sorry if this all sounds a little condescending. I certainly understand the frustration!

Tim

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: napa68</div><div class="ubbcode-body">I have observed a few things in this thread

1. The issue seems to revolve around the distributor. It certainly sounds as though the ground wire to the contact plate is compromised. Excessive shaft clearance could very well be an issue as you approach higher RPM. As mentioned, try a known good distributor.

2. Is the issue in anyway related to engine temp? As mentioned, you could have a coil on the way out. I recently had this on a T.I. LT-1 I used to own.

3. Has the voltage at the positive terminal on the coil been checked both at both cold and warm engine temp? If the harness is original, you are dealing with something 47 years old. Even corrosion at the harness bulkhead can reduce primary ignition voltage (prior to the resistance wire) that would induce a drivability problem.

Sorry if this has been covered somewhere in the thread and I missed it. Don't overthink the problem. Start with the basics.

Once you do determine what your miss truly is, I would not hesitate to send the dizzy out to someone like Jerry M. for an overhaul. I think you would be impressed with the difference!

Sorry if this all sounds a little condescending. I certainly understand the frustration!

Tim</div></div>
Tim
What should the voltage be at the positive side of the coil? Cold and hot? Your comments don't sound condescending. I appreciate the response.
Don't think the problem is centered around the engine temp. But I did see the problem change when I installed a new coil. I.e. miss started at 3500 rpm with original coil. Miss started at 4500 rpm with a aftermarket coil.
I have not had a chance to take out the distributor, but will and plan on examining it real well. Probably will have it rebuilt.

Lawrence