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Author Topic: Honda CB125 S Ignition points / timing - PROBLEM  (Read 219 times)

Offline onelitu

  • Posts: 3
Honda CB125 S Ignition points / timing - PROBLEM
« on: Sep 21, 2018, 19:07:50 »
Hi there, I have a Honda CB125 S.
(I am super new to bikes)

I wanted to follow this video :

About how to adjust the timing on the bike...
- so that it "should always start the first time! "
Currently the bike doesn't want to start ( the battery is fully re charged and there is a new spark plug(with spark tested).

Unfortunately I quickly realised that on my honda
when the rotar is aligned with the letter F the contact points are almost
completely open?
Here is the video - with photos and footage:


How can I fix it?
Thanks for help, your time and any suggestions !

Offline teazer

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Re: Honda CB125 S Ignition points / timing - PROBLEM
« Reply #1 on: Sep 21, 2018, 21:17:33 »
Common question, so let's see if I can help any.

It's a 2 step process.

Step 1: With ignition OFF, rotate motor until points are fully open - that will be at F mark or later and set the points gap.

Step 2: Turn Ignition ON, and rotate the motor again until the points just open.  Determine that time with buzzer, radio tuned off station, timing light, multimeter etc.  You can even take the plug out and plug it into the cap and lay it on the motor so that the metal part of the plug is touching raw metal on the motor ( or use https://www.aliexpress.com/item/Car-Spark-Plug-Ignition-System-Tester-Coil-Engine-In-Line-Adjustable-Ignition-Coil-Tester-12V-Car/32841655033.html )

the timing should be set so that the points just start to open at the F mark.

If it's way off like yours, two things to check.

Is it just out of adjustment at the plate?  You should be able to loosen the two mounting screws and rotate the plate back and forth by a few degrees.  If you are seriously advanced, check that the points cam can move.  Behind the points plate the cam sits on the end of the camshaft and should have two weights that sling out and spring back.  That's the advance retard or Automatic Timing Unit.  They often rust in place.
 

Offline onelitu

  • Posts: 3
Re: Honda CB125 S Ignition points / timing - PROBLEM
« Reply #2 on: Sep 24, 2018, 06:47:26 »
Hi teazer,

Thanks for help!

Your step 1 and 2, its basically what I tried to do- adjust the points with the F mark,
its just seem to be in my case very OFF, not just little bit - as I find examples on youtube...
that is why I dont understand it.

If you are seriously advanced, check that the points cam can move
How can try that ?
They often rust in place
if they are, shall i clean it or buy a new one ?

Thanks you!

Offline teazer

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Re: Honda CB125 S Ignition points / timing - PROBLEM
« Reply #3 on: Sep 24, 2018, 15:11:35 »
Remove the points mounting plate and lay it aside.  You should now be looking at the cam and advance weights.  Just grab the cam by hand and see if it rotates.  It should move a small amount in one direction and should spring back when you let go.

If it didn't run when you got it, it's always possible that the PO had the points cam off and dropped the locating pin.  It's also possible that the camshaft (the one that lifts the valves) is one tooth out on the cam chain.

Offline onelitu

  • Posts: 3
Re: Honda CB125 S Ignition points / timing - PROBLEM
« Reply #4 on: Sep 26, 2018, 06:09:33 »
Hi teazer,

Thanks for help.
We removed the points plate, and see if the springs in the advance machanism - all seems ok.

I tried to push started - and after 15-20 it fired up... when its runs it runs ok.
(it just doesnt want to start cold at all !)

I did a new video:


It's also possible that the camshaft (the one that lifts the valves) is one tooth out on the cam chain.
-Is that the reason why I cant time it properly ? like in my video on the end, where F mark and the breaker points starts to open but NOT on the compression ?
Like its off by 1 spin of a rotar ?

thanks !


Offline teazer

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Re: Honda CB125 S Ignition points / timing - PROBLEM
« Reply #5 on: Sep 26, 2018, 19:15:38 »
The only way to be sure would be to take the engine top cover off and turn the motor to TDC and see if the cam sprocket is in the right place.

A quick and dirty might be to rotate the motor with a wrench and see when the valves open and close.  The point of overlap where both valves are open is close to TDC.