Honda CB125 Superdream only running on one cylinder

locky60 · L Plate Warrior Joined: 08 May 2011 Karma :

Hi don't know if anyone can help,i have got a 1987 Honda CB125 TD-J.I striped the bike down(not the engine) re painted it and put it all back together,but now it only runs on one cylinder and i cant find out why.
It all ran fine before i started i did take the starting motor of the engine and it did sit on its side for a dit,it starts ok and i have got a spark on the cylinder that doesn't work.
Any help would be good thanks Question

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

start with the basics.
You have twin sparks on this bike, so you can nail down the fault by side to side swapping.
Anyway. First of all
Swap plugs left to right, see if spark moves with plug... if so then you have duff plug
Then try swapping coil connections..... see if spark swaps with coils....
IF SO check the earth connections on coils to frame! Highly likely if you have been chucking paint around that's where the problem lies.
Next, swap CDI plugs... see if spark moves....
Finally.... did you remove the generator cover when painting?
If so check that the casing is seating properly at the bottom.
A misaligned alignment dowl, on the bottom holding the casing possibly 2mm off the crank case had me tracing evert bludy wire, and testing every damn component in the system, two weeks ago, until we found out that small 'chink' in the casing, via a plasticine test, meant that the rotor trigger was completely missing the lower ignition trigger!
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locky60 · L Plate Warrior Joined: 08 May 2011 Karma :

Thanks for that,will try them out and let you know how it gose.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Hold on though.

You HAVE got a spark on the non-running side? Is it a good, strong blue spark that jumps directly across the electrode?

Is the plug wet after it's run for a bit? It should be soaked in fuel. If it isn't, there is a problem with the carburettor or the fuel supply to that carburettor. As I remember, if there is a restricted fuel supply, it'll tend to drop out on one cylinder first (usually the right one as I recall).

Also check your airbox. If it's been lying on its side, there could be oil in there clogging the filter.
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Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

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Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

locky60 · L Plate Warrior Joined: 08 May 2011 Karma :

i have got a good spark on both plugs,it is the right one im having probs with and the plug is wet when i take it out.
I am running a two into one exhaust and the carbs are joined by a bar for the chock.
Im going to pull the cards of tomorrow and have a look at the.
Thanks for the help