Author Topic: CB250G5 Ignition  (Read 889 times)

Offline boxie30

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CB250G5 Ignition
« on: November 02, 2017, 09:17:45 PM »
Hi all,

 I have no spark at the points on the left cylinder. I have tested the coils and get the correct ohm reading, also tried a second set of coils and get the correct ohm reading.

 If i swap the wires of  the coils from the left to the right i get a spark from the left spark plug but the left hand points still do not spark. Which makes me think the coils are okay.

The point are brand new and i have gapped and regapped them about 4 times.

I also have checked all the wiring for breaks and all are good.

I did get a spark from the left points while i was gapping them but from the location where the wire is screwed onto the points, but as soon as i gapped them correctly it went away.

Any thoughts as i am at a loss.

 

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Re: CB250G5 Ignition
« Reply #1 on: November 02, 2017, 10:11:35 PM »
It's very often the little insulation washers on the points which are there to stop the wire touching the base plate.

The points are switching the earth wire from the coils on and off,  if there is any connection to earth other than going through the points contact then that system won't work. It may be obviously a washer out of place or it could be a small hairy bit of wire strand poking out of the wire terminal and touching the points bracket.

Offline Bryanj

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Re: CB250G5 Ignition
« Reply #2 on: November 03, 2017, 06:09:49 AM »
Is this with the cover on or off because the cover used to short out one set of points

Offline boxie30

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Re: CB250G5 Ignition
« Reply #3 on: November 03, 2017, 07:53:09 AM »

 I had only screwed the points in, straight out of the box, but i will have a look tonight.

 The cover was on when i got the problem, but has been off while checking.

 Cheers.

Offline AshimotoK0

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Re: CB250G5 Ignition
« Reply #4 on: November 03, 2017, 08:11:24 AM »
In addition to what has already been suggested ... New points often come with protective grease on the precious metal contacts, so make sure that is cleaned off. Did you replace the capacitors ( condensers) or are they still connected correctly? You need the capacitor functioning to get a decent spark. ( they can go leaky or lose capacitance), also make sure the body of the capacitor  assembly is properly grounded to frame.
« Last Edit: November 03, 2017, 08:34:55 AM by AshimotoK0 »
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline boxie30

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Re: CB250G5 Ignition
« Reply #5 on: November 03, 2017, 10:12:54 AM »

 I never thought to clean the points first...... I had just filed them down a tad just in case.

 I had tried two different set of coils but got the same result.

 The condensers do look a little rusty on  top, so i will strip them down and clean everything.

Offline boxie30

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Re: CB250G5 Ignition
« Reply #6 on: November 09, 2017, 12:14:30 PM »

 It turns out it was the brand new (nos) points.

 I have filed them down until the points face was shiny, but they still do not spark.

 I will buy another nos one and maybe a brand new one just in case.

 One question, should the spark at the point be "white" as the spark i am getting from the good side looks orange?

 Cheers.

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Re: CB250G5 Ignition
« Reply #7 on: November 09, 2017, 01:29:56 PM »
Ordinarily they shouldn't spark that much.

When they open the flow of volts tries to get to earth the easiest way and while the gap is just staring to open this is the route it takes, making a spark.
The condenser's role is to absorb this effect and prevent the spark happening, while it's sparking the circuit is still not broken so the coils are not switched and will compromise the activity of the HT coils.

Refer to Ash's point above about condition and earthing of condenser as that is where it appears your problem is.

The fact that they are sparking significantly suggests the points are doing what they need to do, it's the suppression of that unwanted spark that needs to happen to get the coils doing what they should.

Offline AshimotoK0

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Re: CB250G5 Ignition
« Reply #8 on: November 10, 2017, 08:34:17 AM »
This morning I have been scanning the Genuine CB250/360 G5 CJ250/350 Genuine Shop Manual. Been a bit of a ball ache because it was a bound not ring binder type book and it's a really well used copy that came from the workshop at Alan Mountains dealership in York (my mate now has his own bike shop there). This will be a Godsend to you working on that model...I should have it completed by tonight so watch the Aladdins cave section on here. Like I said, check the condensers (Capacitors) .Basically the manual tells you to check that the capacitance is around 0.25uF and the insulation is 10M Ohms or greater ( tested with a Megger). I appreciate you probably don't have the kit to test  but any electrician worth his salt should have a meter with capacitance range on it and a Megger tester. Failing that, If you can squeeze one into a 25mm thick package you can send to me to test as it's only 98p each way to  send it.
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline boxie30

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Re: CB250G5 Ignition
« Reply #9 on: November 10, 2017, 12:39:24 PM »

Thanks for both your replies,

I had tested the condenser and was getting 0.22uf, but had not checked the resistance of the insulation. I have ordered a brand new condenser just to check, before i spend £60 on a nos one.

Ash, I will keep a look out for the shop manual.

Offline boxie30

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Re: CB250G5 Ignition
« Reply #10 on: November 18, 2017, 03:25:22 PM »
 Sorted it,

 The yellow wire from points to coils was frayed, making intermittent contact. It wasn't until i gave it a pull that it snapped, the insulation was intact and it was where it goes through the fins, so was not really looking for it .

 Thanks, (now to find the reason for the high pitched squealing while its turning over)

Offline BigAl (Alan)

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Re: CB250G5 Ignition
« Reply #11 on: November 18, 2017, 06:33:49 PM »
Good advice from Ash again. 'Megger' or '500 volt insulation tester' as my old foreman back in the 70's use to say!.. Image attached of the old cranked-up 'Megger' for anyone who is not sure what one is, no batteries required.
Current bikes:-
Honda CB750 K4 (1974) USA
Honda XL500S (1980) UK
Honda CD175 sloper (1968) UK
Honda CB1100A (2013) UK
www.alans-electrics.co.uk

Offline AshimotoK0

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Re: CB250G5 Ignition
« Reply #12 on: November 18, 2017, 08:02:23 PM »
Glad you got it sorted

Will be about a week before i can get Service manual as bit of a hiccup with the scan (very well thumbed ex-dealer copy)

Squealing may be from 'starter' sprag clutch mounted behind the alternator rotor. Normal whilst turning over but should disappear once started. can sometimes be housing breaking up (particularly on early CB450) or just tiny springs, rollers and pins that need replacing (still available from Honda and Dave Silver).
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

 

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