SOHC.co.uk Forums > CB500/550

tickover problem

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Bryanj:
You will not get a reliable tickover till the motor is HOT, if you set the tickover to about 1100 on the big screw after a ride of several miles you will find you have to "hang" the throttle when cold.

I can count the motors that tickover reliably at less than 1100 on the fingers of one hand in 30+ years mate

mickwinf:
Bryan I set carbs after a good run, trying for a tickover speed of 1100-1200 but even at slightly above this it will idle evenly for a few seconds then suddenly drop below 1000 revs and stall, just as I am trying to set mixture screws! It normally does not need any choke to start, suggesting a rich mixture, will only idle reasonably if the mixture screws are 2 full turns out, is it turn out to richen? It actually is better when engine has just started, worse when hot, again suggests a rich mixture. Just going to have another go, wish me luck!

mickwinf:
thanks Oddjob, this weekend I am going to strip carbs (again) and double-check everything, then re-fit with new carb rubbers both carb to head and carb to airbox. Will also check all other settings but am sure all ok. One other thing, I have a new drain tube which I thought fitted to bottom of the air filter box, but does not have a connection on it, but looks too small to fit on the air collector box behind carbs. Where do I fit it?

mickwinf:
well I spent a few hours stripping carbs, everything internally very clean, the only thing I could see wrong was the floats were a bit twisted so I spent some time straightening them out and reset float hights. Re-fitted with new rubbers so definitely no air leaks. Now It is better and will tick over for longer but still will suddenly drop revs and stall. will try again tomorrow!

fisjon:
If your carbs were ultrasonically cleaned as one unit it is possible that the fuel connector seals may be perished. Rubber or plastic placed into an ultrasonic cleaner can degrade very quickly. If they were original fit then they wouldn't take long to disintegrate. Also the core plugs can dislodge and/or fall out completely if the fluid was being used at the 60-80 degrees recommended by the cleaning fluid manufacturer. I have found a few in my bath and have resealed them back into the carbs with resin. Another thing I have found is two lots of rubber seals in the air screws and sometimes no flat washer to go between the spring and air screw seal.

If the engine slows down gently before conking out then it may be fuel flow, but this would be apparent at higher speeds so if your bike runs good except for tickover and conks much without warning then it is probably electrical. As the engine slows down the electrical output is marginally reduced and there may be a gremlin due to a faulty regulator or a bad earth somewhere on the bike that is affecting the spark train. All it takes is for a momentary loss of spark and the motor will hunt and stall.

I fitted my CB650Z with a Boyer unit, totally ripping out the Honda stuff and the bike absolutely refused to stall. The spark was like an arc welder! I used a plug on the side of the engine to test it when I first fitted it and I have never seen a spark so bright. It also make a cracking sound and frightened the s**t out of me.

Food for thought

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