Topic: CB550K3 airleak question

[tg305]

I have the much discussed throtle idle issue with my 78 CB550K, where it take a while to settle down and races periodically.  I bench synced the carbs recently and replaced the intake rubbers with brandy new ones.  Also I replaced the plastic tubes between the carbs because one was cracked and leaking.  When I spray WD40 or carb cleaner on the carb units (specifically the internal two) my idle races upward to 3000 RPM.  Can I be leaking air from somewhere else other than the two locations I worked on.  My intakes are air tight   when I spray on them there is no change in the idle......   thanks   Tim

I do plan on buying some carb syncronizers this week.  The carbs were cleaned a month or so ago and I used guitar string to clean out the idle jets after I removed them so they are nice and clean. I've also run a few bottles of Seafoam through the carbs too

[Dennis]

Can leak at the head. O-ring between aluminum carb mount and head.
I haven't heard of this being a problem, but if you suspect an air leak, it's easy enough to check.

[TwoTired]

If there is excessive slide to carb body wear, air can leak past it at different rates depending on where it happens to settle after the last movement.  There are gaskets on the top carb cover top prevent most of this.  Is this what you are spraying when the idle picks up?

Maybe you should renew these gaskets after your carb sync?

[tg305]

I bought one carb gasket kit and applied the P shaped gasket on top where I thought it may be sucking some air.  The idle doesn't raise when I spray on that area.  It does idle up when I spray the center of one of the two center carbs (can't remember which one at the moment).  Kind of in the area where the fuel crossover tubes are and the choke linkage is. 

Tim

[TwoTired]

Well unless you have cracked carb bodies...
I notice on the carb set on my bench, that the choke butterfly pivot bar is pretty loose in the carb body and it can't possibly seal well there.  That area is under vacuum, and it would be higher when the air fliters were active.  Putting fluid on the pivots would allow it to get sucked into the carb, and if it were thick enough, increase the vacuum for that carb.

This may be another symptom of carb imbalance.  Particularly if that carb was bordering on being ineffective due to its slide setting.

 Just a theory...

[tg305]

Thanks guys, I'll take a step back and sync the carbs and see where I end up.  Tim