tickover problem

[mickwinf]

For the life of me I can not get a good reliable tickover on my 500/4. Everything is as standard including exhaust, no air leaks new filter, carbs have been cleaned several times, ultrasonically and carb cleaner plus airline. All service items are spot on, bike runs great in all other respects, pulls away with no flat spots and revs up to the redline no problem. I rebuilt the carbs with a keyster kit and set float hight correctly using a special tool. I have tried substituting the original mixture screws but no change. The best idle is obtained with screws 2 full turns out, more than the workshop manual says. When idling at first it seems ok, then after a few seconds it will falter and stop. It also hangs on to the revs slightly when I rev and return to tickover. Also carbs have been balanced with vacuum gauges. Any tips ?

[busa]

sounds daft mick.  have you checked your throttle cables are push pulling  ok  and are not restricted anywhere.  I have had problems with newer bikes  (race bikes)  especially Hondas  for this.  similar thing,  turned out to be throttle cables.  Also   is there an O ring on the Mixture screws.   could be that  leaking.

might be wrong.  just a thought.

regards   colin

[mickwinf]

Yes Colin cables are new and have a bit of free play, carbs snap shut when throttle closed, its doing my head in!

[busa]

the needles are not bent are they?   have you altered position of needles. choke butterflies  screwed on tight (not loose on bar)
sorry mate  just  racking my brains for you.   O rings on fuel link pipes  the ones that link each carb.   or blank ends on the choke arm on the out side of No1  and No4 carb  this is like a little core plug.  Breather on tank,  or filter in tank,   kink in fuel pipe  etc.   timing slightly out.  (advance/retard Plate).  synch screws in tight   inlet manifold rubbers could be leaking(ones that are against the head.  you could test.  when engine running  spray WD40  over them  see if engine revs pick up.   if so there is you leak (I think you would already know this anyway) 

its drawing  air  or lacking fuel somewhere  at low RPM.
hope these suggestions  help

[mickwinf]

I have checked for air leaks as that is the common cause of erratic running, all internals are new and set to stock positions. I did think about putting original jets and needles back in but bike runs great except this tickover problem. Will check again for air leaks and report back.

[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

[mickwinf]

Carbs were stripped prior to ultrasonic cleaning and all new rubbers fitted afterwards. I hadn't considered electrical but will check it out. It is better but not perfect yet.