The International CBX Owners Association

I have gone through the carbs on my 79, i'm sure the slides are spick and span clean, all new gaskets, jets, etc etc.. For some gosh darn reason when I stop the bike it will high idle for 30-40 seconds before dropping to a normal idle?????



Any suggestions on cause?



L.

1.) The carbs are not sync'd.

2.) possible air leak

Probably carbs not in sync. :P

Does your throttle snap shut or does it return slowly? Could be a sticky cable or throttle.

Also, make sure your choke is adjusted properly. Eric

I find both my CBX's do the same. I've also noted that if I am at a stop light or such that I can decrease the idle by SLOWLY letting the clutch out to load up the engine and then the idle will be fine, until I rev the engine up again. Go figure.

I've replaced the intake boots, had the carbs balanced and checked for intake leaks. Must be a sticky slide and the vaccum created once I load the engine down pulls it back down....... I think. Any other ideas?

Classic symptoms of out a balance carbs.

turn bars side to side while'ist running at idle should determine any cable kinks/binding. does it snap back to the stop?? if so, I'd re-check the sync.

Problem with high idle is probably due to valves adjusted to tight. I think some of the early manuals called for min. clearance of .0015 but this was later changed to .003". I would set them at .004 - .006 for best results. This problem was also common on early v-4's when valves were too tight.

Here's a new Tech Tip I'm writing for my Honda GL1000 website.



Since these bikes are of similar vintage and carb config, the same general issues apply. Obviously, you can ignore the GL1000-specific details.



(this is copyrighted material)



Tech Tip: Lazy / Slow Return to idle (or erratically high idle)



Are you plagued with a bike that runs great from about 2000 rpms and up, but refuses to idle reliably below that speed? Does it sometimes idle OK, but often "hang-up" at a higher speed and take forever to return to idle? Do you have to put a small load on the engine (by letting out the clutch a bit when stopped and in gear) to get the engine to return to idle speed? If so, read on.



Assuming you didn't make any mistakes with the carb rebuild (which is all too common), and you've eliminated ignition issues, the normal suspects for a lazy, high idle are:



(Ignition problems such as incorrect timing or a stuck advance mechanism can create similar symptoms)

• Poor / uneven compression values
  
  Poor carb synch
  
  Vacuum leak
  
  Improper re-mating of carb pairs (there should be a washer on either side of link which joins the throttle butterfly shalfs of each carb pair on the left and right sides)
  
  Linkage or throttle cables binding or not enough freeplay
  
  Choke not releasing completely
  
  Dirty / blocked idle circuits in carb
  
  "Sticky" CV slides
  
  Overly lean for any number of reasons
  
  Problem with Air cutoff valve or it's vacuum hoses (this usually causes a back-fire)
  
  Mis-matched float heights

Poor carb sync is most common reason for your complaint. The reason for this, is that when the carbs aren't synched well, one or more cylinders have to compensate for the underperforming ones (at idle). This gets the harder working cylinders into the progression fuel circuits (at idle) to maintain proper curb idle. This creates a problem in coasting situations because there is too much fuel metered out. It only takes a small extra amount of fuel in low/no load situation to cause an unnaturally high idle. To make matters worse, this usually activates the centrifugal ignition advancer and you get wild oscillations in idle speed.



A related and common cause is blocked idle circuits. Again, one or more cylinders have to compensate for the one(s) not contributing at idle. You then have to screw the idle screw in to the point that the progression circuits are activated. Havoc ensues.



The idle circuitry involves ALL of these components:

• #35 idle fuel jet (under the rubber plugg between the primary and secondary main fuel jet towers). This is a VERY small orifice and easily compromised by debris in fuel.
  
  #110 or #115 idle air jet (external - in the brass elbow) This should be modified to fix "off idle" glitch: http://www.randakks.com/TechTips.htm#6
  
  3 idle fuel transfer ports located under the "puck."
  
  idle mixture screw
  
  myriad fuel and air passages in the plenum and individual carb bodies.
  
  air cut-off valve (prevents back-fire on overun)
  
  float bowl gasket (really!)
  
  clear fuel inlet screens (under each float valve)
  
  proper float settings
  
  clean, flltered fuel
  
  proper fuel pump pressure

Even though you may have performed a carb sync., it doesn't mean you necessarily got a good one. GL1000s are very sensitive to carb sync. Ditto for float height!



Unfortunately, these variables are all inter-related. Everything has to be on-spec for proper performance. The idle circuits in a GL1000 are ridiculously small, so slight problems are greatly magnified.



To summarize, the solutions for a Lazy / Slow Return to idle (or erratically high idle) are:

• Perfect ignition
  
  Perfect idle circuits - usually requires a throught carb overhaul, but this is worth trying: http://www.randakks.com/TechTips.htm#1
  
  Perfect float settings
  
  Perfect synchronization

Randall! Long time no hear! Your first post. Neat! Folks, if you don't know Randall, he is one of the very few real authorities on vintage Hondas. Visit his site and find out how much experience is distilled into those few pages. Man, glad to see you on this board! Neat!

Great post Randall, thanks for the in depth explanation. Now go out and buy a CBX and join us at the Morganton CBX National rally in NC June 19th-26th.



Bring whatever you want but come on down for a day or so.



jeff

Mike is too kind.



Sorry to hijack the thread, but I might be able to attend for a day of the Morganton event. I'll be checking with the authority on my schedule "flexibility."



My '75 GL1000 show bike needs some exercise, so it would be a good chance to meet some other vintage Honda enthusiasts.



I've never owned a CBX, but I "need" one badly!