Author Topic: No ignition sparks at the plugs  (Read 463 times)

Offline Gary400/4

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No ignition sparks at the plugs
« on: October 07, 2019, 11:46:44 AM »
Hello all, I have been toiling away over a couple of years in my shed resurrecting a forlorn cb400/4. The problem I now have is trying to get it to run. Engine is rebuilt, good compression engine turns over on the starter motor. I have 11.7 V measured at my ignition points terminal. This means current has flowed through my primary windings in my coils then out on to my yellow and blue wires. I can manually open the points to obtain a spark across them. The points are timed to start to open at the F1-4 and F2-3 marks. I have fitted new capacitors. Points gap set at 14thou of an inch.
The coils are Tec FL703 type, the primary resistance measured at approx 5.5ohms the secondary windings measure at approx 12Kohm. Without suppressor plug caps.
I have also noted that when the points open, if a analogue meter is used the pointer will drop towards zero. If I use a digital meter. The low resistance across a closed set of points should go quite high in terms of open circuit resistance, when the points open. But I am detecting 7 ohms of continuing continuity. Suggesting a resistive open circuit short circuit to ground. This has me thinking this is offering my ignition voltage  a low resistance path to ground, lower than having to energise a collapsing electrical field inducing an emf into the coil secondary windings. It's all well and good putting new coils on, I am not 100% convinced that will solve my lack of spark problem.
On the points, I do wonder if the tiny insulting ring that passes through the the terminal screw tab, and has insulated discs either side, can loose some resistance.

Offline taysidedragon

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Re: No ignition sparks at the plugs
« Reply #1 on: October 07, 2019, 01:13:29 PM »
It's difficult to diagnose the problem without seeing it up close.

I would check that the points wiring and insulators are connected in the right sequence. Then check continuity on the wiring all the way from points to the coils and double check that the coil connections are the right way round!
It's unlikely that both coils are faulty, but they might be. If you can get hold of a known good coil, try that in place of one of the existing coils. Hope that helps.
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Offline SteveD CB500K0

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Re: No ignition sparks at the plugs
« Reply #2 on: October 07, 2019, 02:29:37 PM »
Did you say that you get a spark at the plug when you manually open the points?


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Offline mike the bike

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Re: No ignition sparks at the plugs
« Reply #3 on: October 07, 2019, 02:34:46 PM »
You can simulate points by shorting the blue (or yellow) to ground and then disconnecting.   When you disconnect, you should have a spark.
This test should prove the coils to be good or bad.
« Last Edit: October 07, 2019, 02:36:48 PM by mike the bike »
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Offline Bryanj

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Re: No ignition sparks at the plugs
« Reply #4 on: October 07, 2019, 02:55:39 PM »
Sounds like maybe corrosion or preservative on contact surface.
If not and spark occurs when you manualy open the points with everything connected the cam is either/or/both not opening points enough or at correct time

Offline Gary400/4

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Re: No ignition sparks at the plugs
« Reply #5 on: October 07, 2019, 09:38:53 PM »
Thanks for the input. I am still non the wiser. The points are still serviceable given that they are gapped and the fibre heels mean that they are still within adjustment to time the moment when the points to the F1-4 and F2-3 marks start to open. The blue wire is paired to coil serving cylinders 1-4 and corresponding set of points. Conversely the yellow one serves the coil to cylinders 2 and 3. The black and white wire which  carries ignition voltage common to both coils. The black wire within the loom is a positive supply to all of the ancillary components. Because continuity exists between live and ground via the resistance of bulbs in the console, there are 3 common green ground wires between hi beam and the indicators. I am wondering if this is causing me to detect this  at the points? I have seen replacement coils for the FL703 on eBay at around £25 each. They are push fit HT leads with screw locking caps.
 Should I be detecting continuity of around 7 ohms between the points terminal wire and ground when the points are open or should this be closer to infinity? To know for sure will help me with my investigation.

Offline Lobo

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Re: No ignition sparks at the plugs
« Reply #6 on: October 07, 2019, 09:55:04 PM »
There are many possible points of corrosion in the ignition circuit, and as a first port of call you might try hot-wiring the coils directly to the +ve of the battery.... ie cut out the ignition switch, kill switch, and old wiring / bullets in the original feed. Of course, also ensure the points back plate is securely earthed.  If this solves your problem you’ll then have to work backwards checking the aforementioned components in turn.

Online Moorey

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Re: No ignition sparks at the plugs
« Reply #7 on: October 07, 2019, 09:56:48 PM »
Welcome to the forum. I see your already having fun. ;)

Offline Lobo

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Re: No ignition sparks at the plugs
« Reply #8 on: October 07, 2019, 10:00:27 PM »
... at some point today I’ll measure the resistance figure you seek on my (working!) 400F.

Addendum... Doh, and sorry Gary, my 400F has a breakerless ignition, and to get what you want would mean a fair bit of disturbing things. My excuse is 7am writings and 5 different bikes... forgive me!

I agree the ‘idiot’ lights would induce a reading, but don’t forget that the test you describe will also include the respective coil primary winding and the voltage regulator resistances. (The VR, I think, will be feeding the alternator field coil at 0 rpm. (My ‘750 book suggests this field coil is rated at 7 Ohms & I’d guess the 400F same-same). Anyways, point is, if you disconnect the Regulator, take out the Oil Pressure lamp, put the bike in gear (Neutral lamp out), all lights off etc... then your yellow / blue test circuits should only be measuring their respective Primary coil resistances. And if these 2 values (ie Yellow & Blue) are the same, then that’s a good sign.....though not proof of a healthy ignition system.

I still reckon your best staring point is as per my earlier post; for my money the culprit might be the kill switch which has weeny contacts, carries a couple of amps, is prone to water ingress, and whose loom is always on the move.
« Last Edit: October 08, 2019, 03:27:42 AM by Lobo »

Offline mike the bike

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Re: No ignition sparks at the plugs
« Reply #9 on: October 08, 2019, 12:15:59 PM »
In other words.... have you got 12V on the black/white wire going to the coils?
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Offline K2-K6

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Re: No ignition sparks at the plugs
« Reply #10 on: October 08, 2019, 12:30:57 PM »
Just a reality check for orientation,  if you swap the yellow and blue wires to the points and then try starting.

It's just that sometimes they've been assembled (not factory)  with them trying to fire the cylinders at bottom of stroke and swapping the two wires will check that for you.

Offline taysidedragon

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Re: No ignition sparks at the plugs
« Reply #11 on: October 08, 2019, 12:56:31 PM »
Just a reality check for orientation,  if you swap the yellow and blue wires to the points and then try starting.

It's just that sometimes they've been assembled (not factory)  with them trying to fire the cylinders at bottom of stroke and swapping the two wires will check that for you.

He says he has no spark at the plugs at all.
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Offline K2-K6

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Re: No ignition sparks at the plugs
« Reply #12 on: October 08, 2019, 01:48:58 PM »
Just a reality check for orientation,  if you swap the yellow and blue wires to the points and then try starting.

It's just that sometimes they've been assembled (not factory)  with them trying to fire the cylinders at bottom of stroke and swapping the two wires will check that for you.

He says he has no spark at the plugs at all.

My mistake,  read the spark description and failed to consider it was "across the points"  yep different problem.

 Edit:- battery voltage would normally be closer to 12.7 in a healthy system as comparison to the level currently.  May not make the difference but you'd ideally need to get it closer by charging or using jump leads from another.

Generally if you fully charge a battery and leave it alone,  then 11.7 volts residual would suggest it's impaired.
« Last Edit: October 08, 2019, 02:28:14 PM by K2-K6 »

Online Moorey

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Re: No ignition sparks at the plugs
« Reply #13 on: October 08, 2019, 07:09:23 PM »
Just a reality check for orientation,  if you swap the yellow and blue wires to the points and then try starting.

It's just that sometimes they've been assembled (not factory)  with them trying to fire the cylinders at bottom of stroke and swapping the two wires will check that for you.

He says he has no spark at the plugs at all.

My mistake,  read the spark description and failed to consider it was "across the points"  yep different problem.

 Edit:- battery voltage would normally be closer to 12.7 in a healthy system as comparison to the level currently.  May not make the difference but you'd ideally need to get it closer by charging or using jump leads from another.

Generally if you fully charge a battery and leave it alone,  then 11.7 volts residual would suggest it's impaired.

The 11.7v is at the points not at the battery. So his ignition is on and warning lights so not too bad really.  If it was 11.7v on the battery alone after charging then it would be knackered.

Double check  your insulator set up on the points 7ohms is nearly straight down to earth. Disconnect the condensors and try again .
 
« Last Edit: October 08, 2019, 07:25:28 PM by Moorey »

Offline Gary400/4

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Re: No ignition sparks at the plugs
« Reply #14 on: October 09, 2019, 12:22:07 PM »
Many thanks for your further insights, relative to my ignition problem, I take note the kill switch is s potential cause for
concern, grounding faults, chaffed insulation. I will check mine, I agree with the remark that the insulators within the points might be suspect, current might be tracking through to ground? I will remove the items causing resistance within the ignition circuit. As a precaution.

The fact is, 11.7 V DC is detected across the points, given that the battery voltage has flowed through the wiring loom including the primary windings within the coils, switch gear etc. Indicates a healthy Voltage at the points. But I don't think the coil electro magnetic flux and capacitor voltage is being induced into the secondary windings, when the points open, given that the primary voltage has an easier route to ground because of the 7 ohms resistance to ground. I am detecting. I might as well buy a new set of points, to see if that helps. Years ago it was a forgone conclusion to change the points and condensors together. When I used to own a 550/4 I always carried a spare set of condensers, because 9 times out of 10 it was the condensors or one of them, which gave up the ghost causing the engine to limp along firing on 2 cylinders. Which is why I have serviced the points and replaced the condensors for new from Dave Silver spares.