SOHC.co.uk Forums > CB500/550

Trouble with bike

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deltarider:

--- Quote from: beardylondon on February 21, 2025, 04:47:17 PM ---[...]
It is at my Dad's, [...] He is only familiar with old British bikes, he has tried all the normal things, but can't get it to start. Battery is good, fuel is good. He thinks perhaps points.
--- End quote ---
So your dad thinks it's ignition related. Let's start there. What was the reason you replaced the coils?
First question is, are the plugcaps connected well? Are plugcaps themselves still OK?
Then to the points. Are points surfaces clean? Do NOT clean them with paper or carton like business cards. I've learned from personal experience that some residu of it can prevent points from contacting.
When you manage to have it run 'lumpy and spluttered', this video may help you diagnose a faulty condenser: https://www.youtube.com/watch?v=t3cuvGVwnjI At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner
If you can't get the engine to run, Youtube has tutorials on how to test a condenser aka capacitor. You don't need a Fluke, any cheap DMM will do.  https://www.youtube.com/watch?v=gg2emZ91mxI from 01:30 on. I'm suggesting this because you fitted new coils. When people suspect the coils, in many cases the condenser(s) is/are the real culprit.

andy120t:
 If it was running before, then unless anything has changed I would assume it'll start again..but maybe something is blocked.
My Zephyr 550 was running poorly after sitting for a while so I used Valvoline Carburettor Cleaner which, once the engine is hot  ( and I used easy-start to get it running because it wasn't starting) is sprayed into the air intakes, the leave the engine running for a bit...and it cleans out the gummed up stuff. On mine I could hear the moment when the carbs suddenly cleared up and it began to run properly. Saved me taking off the carbs and cleaning them out.

beardylondon:
It started up, wasn’t kill switch.

It will tick over and when revved it pops and sputters badly, on idle, without touching the throttle it will randomly increase revs.

The mystery continues…

I will check out above, re: condenser, thank you!

Carb cleaner a good shout too!

Johnwebley:
I occasional tip a good measuring of Redex carb cleaner in the tank,

That will get inside the system

Hopefully clear it out

Sent from my SM-A546E using Tapatalk

K2-K6:
It's very often some level of restriction within the idle jets and their circuits.

Carb cleaning products worthwhile trying as a simple non invasive way to assess if it'll improve.

The slow/idle modulation does so much on these carburettor, making it look like serious fault is present when in reality it's these.

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