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dfwallis 
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Joined: 09 Mar 2023
Location: DFW
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 Topic: CA erratic spark
Posted: Yesterday at 3:33pm |
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Analyzing spark via a gtc505 analyzer. All 4 cylinders look horrible. Cylinder 1 and 4 have the best signals but 2 and 3 are spiking randomly. All have a peak voltage of around 6kv, but 2 and 3 have extra random spikes to 9kv. Suspect random short circuit through cap or wires or other...all is new. My brother says it behaved the same in the 80s. It is running better with new venturi in carb, corrected spark plug gaps. I think to get higher spikes, the dwell time must randomly increase?? Does not seem to be any side to side distributor play, but there is up and down (in/out) play. Suggestions?
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1952 CA13092
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steve(ill)
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Joined: 11 Sep 2009
Location: illinois
Points: 85906
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Posted: Yesterday at 3:36pm |
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i always suspect a weak condenser or coil when i have problems..
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Like them all, but love the "B"s.
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Stan R
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Joined: 03 Dec 2009
Location: MA
Points: 972
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Posted: Yesterday at 3:52pm |
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Last electrical tune-up was in the 80's? I'd throw in new points, condenser, wires, cap and rotor in it. And go from there if still problematic. I'm sure your time is worth more than the cost of these items.
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jaybmiller
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Joined: 12 Sep 2009
Location: Greensville,Ont
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Posted: Yesterday at 4:18pm |
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Distributor shaft float? Yep, I’ve seen that a dozen times on old CA tractors. That’s your gremlin right there. New cap, new wires won’t fix it till you take out the slack. Re-bush or swap that dizzy
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3 D-14s,A-C forklift, B-112
Kubota BX23S lil' TOOT( The Other Orange Tractor)
Never burn your bridges, unless you can walk on water
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dfwallis
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Joined: 09 Mar 2023
Location: DFW
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Posted: Yesterday at 4:48pm |
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Stanr...Those are all new...completeish rebuild...from the waveforms, I think the coil is fine. I think more likely erratic points...the analyzer also gets confused with lots of extra pulses, declaring rpm 5000 instead of 1040 momentarily...cylinder 2 and 3 mostly.
Edited by dfwallis - Yesterday at 4:55pm
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1952 CA13092
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Les Kerf
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Joined: 08 May 2020
Location: Idaho
Points: 1104
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Posted: Yesterday at 4:59pm |
 dfwallis wrote:
Analyzing spark via a gtc505 analyzer. |
I am not familiar with that analyzer, is it an actual oscilloscope?
dfwallis wrote:
All 4 cylinders look horrible. |
Please describe "horrible". Is this at idle?
dfwallis wrote:
Cylinder 1 and 4 have the best signals but 2 and 3 are spiking randomly. All have a peak voltage of around 6kv, but 2 and 3 have extra random spikes to 9kv. |
Do you mean that there are additional spikes other than the one, correct voltage spike?
When the points open, the electro-magnetic field in the coil collapses; the resulting 'flyback effect' induces a voltage in the secondary windings of the coil. This voltage increases until the spark is able to jump the gap. It is not unusual to have variations in the firing voltage as an engine runs; I would not be alarmed seeing 6-9kV ranges.
dfwallis wrote:
... I think to get higher spikes, the dwell time must randomly increase?? ... |
No. The required firing voltage was higher on that particular event. In order to fire at all, the dwell had to be at least 'adequate'.
The first two things I would want to know is what each cylinder has for compression, and next would be to hook up a vacuum gauge and see what that looks like.
Also, do you have any way to take analyzer readings under load? That would be most interesting.
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Les Kerf
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Location: Idaho
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Posted: Yesterday at 5:04pm |
dfwallis wrote:
Stanr...Those are all new...completeish rebuild...from the waveforms, I think the coil is fine. I think more likely erratic points...the analyzer also gets confused with lots of extra pulses, declaring rpm 5000 instead of 1040 momentarily...cylinder 2 and 3 mostly. |
You posted this while I was composing my previous answer.
Your points might be bouncing around, also poor grounding can give fits. The breaker plate needs to be well-grounded to the outside.
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dfwallis
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Joined: 09 Mar 2023
Location: DFW
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Posted: Yesterday at 5:22pm |
Les Kerf wrote:
dfwallis wrote:
Analyzing spark via a gtc505 analyzer. |
I am not familiar with that analyzer, is it an actual oscilloscope?
dfwallis wrote:
All 4 cylinders look horrible. |
Please describe "horrible". Is this at idle?
All speeds.
dfwallis wrote:
Cylinder 1 and 4 have the best signals but 2 and 3 are spiking randomly. All have a peak voltage of around 6kv, but 2 and 3 have extra random spikes to 9kv. |
Do you mean that there are additional spikes other than the one, correct voltage spike?
I suspect these are additional spikes because the analyzer thinks the rpm jumps from 1040 to 5000.
When the points open, the electro-magnetic field in the coil collapses; the resulting 'flyback effect' induces a voltage in the secondary windings of the coil. This voltage increases until the spark is able to jump the gap. It is not unusual to have variations in the firing voltage as an engine runs; I would not be alarmed seeing 6-9kV ranges.
Yes, I have a masters in electronics.
dfwallis wrote:
... I think to get higher spikes, the dwell time must randomly increase?? ... |
No. The required firing voltage was higher on that particular event. In order to fire at all, the dwell had to be at least 'adequate'.
The first two things I would want to know is what each cylinder has for compression, and next would be to hook up a vacuum gauge and see what that looks like.
Also, do you have any way to take analyzer readings under load? That would be most interesting.
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Cylinder 1 and 4 do not experience the additional spikes to 9k or more at all. Gtc505 is a scope of sorts. I have images but too painful to edit and upload on android.
Edited by dfwallis - Yesterday at 5:24pm
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1952 CA13092
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Les Kerf
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Location: Idaho
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Posted: 21 hours 54 minutes ago at 8:43pm |
dfwallis wrote:
... Does not seem to be any side to side distributor play, but there is up and down (in/out) play... |
jaybmiller wrote:
Distributor shaft float? Yep, I’ve seen that a dozen times on old CA
tractors. That’s your gremlin right there. New cap, new wires won’t fix
it till you take out the slack. Re-bush or swap that dizzy |
After ponderizing about this for a while I believe jaybmiller is right. The vertical play in the distributor shaft can make the points chatter about due to the spiral gears causing the shaft to advance and return rapidly.
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Trinity45
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Joined: 17 Mar 2014
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Posted: 21 hours 11 minutes ago at 9:26pm |
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I had problems with my B, thought it was points, then change the coil and the cap, lastly replaced the condenser and that fixed my problem.
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DiyDave
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Joined: 11 Sep 2009
Location: Gambrills, MD
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Posted: 13 hours 54 minutes ago at 4:43am |
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Check the insulator block that carries the points wire through the side of the distributor for cracks, and to see if the points wire has one ear grounding the points at that point...
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dfwallis
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Joined: 09 Mar 2023
Location: DFW
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Posted: 11 hours 8 minutes ago at 7:29am |
DiyDave wrote:
Check the insulator block that carries the points wire through the side of the distributor for cracks, and to see if the points wire has one ear grounding the points at that point... |
I will check...there was a grounding issue that I fixed...got shocked adjusting timing while running, touching the housing, but did not change the behavior when I fixed the grounding (paint). I did check that the points plate is grounded.
Edited by dfwallis - 11 hours 1 minutes ago at 7:36am
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1952 CA13092
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ekjdm14
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Joined: 20 Aug 2024
Location: Manchester UK
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Posted: 9 hours 43 minutes ago at 8:54am |
What are the run symptoms from this? Spluttering/missing randomly?
I've not scoped the signal but believe I'm having a similar issue on the redneck B & (timing "fluttering" all over the place due to slack in it's ignition timing chain setup, needs a new bit of chain. So could be caused by the lash in your distributor in your case
Also, if the condenser is new new & not NOS then perhaps switch back to the previous one/a known good one. Modern parts are/were trash last I checked.
Edited by ekjdm14 - 9 hours 42 minutes ago at 8:55am
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Stuck Farmer
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dfwallis
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Posted: 9 hours 13 minutes ago at 9:24am |
Sorry for posting inside the quote...android ui sucks
ekjdm14 wrote:
What are the run symptoms from this? Spluttering/missing
Runs perfect for short bursts, then random misfires. Also seems to be some sort of cyclical change to timing once every few seconds...engine slows slightly similar to what occurs when you retard timing, then goes back to normal. This is only noticeable if you set timing to extra retard to begin with.
I've not scoped the signal but believe I'm having a similar issue on the redneck B & (timing "fluttering" all over the place due to slack in it's ignition timing chain setup, needs a new bit of chain. So could be caused by the lash in your distributor in your case
Also, if the condenser is new new & not NOS then perhaps switch back to the previous one/a known good one. Modern parts are/were trash last I checked.
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Edited by dfwallis - 9 hours 11 minutes ago at 9:26am
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1952 CA13092
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ekjdm14
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Joined: 20 Aug 2024
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Posted: 8 hours 42 minutes ago at 9:55am |
Not a problem, posting from a 'phone must be a real PITA! This is kinda like mine now I think about it, acts like it was going to clear up and then back to misbehaving. thought I was losing fuel initially but pretty sure it's timing slop.
Would certainly attend to the distributor on your tractor, especially as Jay has experience of this being a cause.
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Stuck Farmer
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orangeman
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Posted: 3 hours 55 minutes ago at 2:42pm |
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I would check the play or displacement in the distributor shaft, possibly worn main shaft bushings? ~ Orangeman
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