Author Topic: Help with Timing issue, I hope  (Read 864 times)

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Offline PeWe

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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Deltarider

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Re: Help with Timing issue, I hope
« Reply #26 on: February 15, 2023, 04:25:41 AM »
I believe you are correct. I made a little DIY "test light" with a small incandescent bulb and some wires. Seemed to show proper circuitry with the points.

[...] Here is a video of the points with the engine running.

https://youtube.com/shorts/y8_JX3qRfV8?feature=share

I don't think Im supposed to see arching on points 2-3. Bad condenser? Thats what Im hoping for. whatya think?
I agree. Easy to check. Just connect the 2+3 condenser to the 1+4 breakerpoints (and vice versa) and see if that arcing follows.
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Offline TwoTired

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Re: Help with Timing issue, I hope
« Reply #27 on: February 15, 2023, 07:09:31 AM »

I don't think Im supposed to see arching on points 2-3. Bad condenser? Thats what Im hoping for. whatya think?

I wouldn’t expect the condensers to eliminate all the contact arcing, just most of it.

When the coil is releasing it energy to the spark plugs, it also creates some energy in the primary side of the coil which feeds back to the point contacts (200 - 400 volts). This is enough voltage to arc at the nearly closed contacts.  Good  condensers should absorb most of this voltage.  Poor ones less so.  But, if your test light isn’t going out when the contacts close, this indicates a poor contact or resistive contact path which has the effect of increasing seen arcing.

Have you tried a point file?  Sandpaper leaves grit embedded in the contact surface that can block or impede large area contact.  The reduced contact area increases resistance.  Perhaps enough to allow your test light to glow.  If you have a multimeter, you could measure the voltage across the closed points. (Key on). It should be zero.
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Offline TimboTec

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Re: Help with Timing issue, I hope
« Reply #28 on: February 15, 2023, 09:03:12 AM »
Wow, I had no idea. All the videos i’ve watched all show the timing being set this way. Does this mean that every one of them, including mine has bent parts?

Also, has anyone had a second to take a look at the short video I linked a few posts above with the engine running with the point going? Is that a normal amount of Arching? Do I also have a bad condenser?

thanks all!

Offline Deltarider

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Re: Help with Timing issue, I hope
« Reply #29 on: February 15, 2023, 09:35:57 AM »
Timbo this vid may be helpful. At the breakerpoints a tiny bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. So in this vid the left condensor (1+4) is bad, right condensor (2+3) is good. So this vid shows a situation the opposite of yours. Just swap the condensers and see if then you have the arcing at 1+4 breakerpoints. If so, that particular condenser is bad. Please report back after you have done what I advised. See to it all is connected well, that the forked connectors do not touch the plates and screws there and that the bodies of the condensers make good contact with the plates.
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Offline TimboTec

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Re: Help with Timing issue, I hope
« Reply #30 on: February 15, 2023, 09:53:07 AM »
Thanks, yes that looks like what is happening
 on my bike. I have to go out of town for a few days but i’ll swap condensers and report back when i return.

Thanks all!