Topic: Idle Issue Tracked Down

[550Resto]

Hello all, I am a proud owner of a 78 CB550 that I've been having some slight issue with. I've got a slightly hanging/high idle that I can't seem to fix. I've got delkevic 4 into 1 exhaust with stock slows and 100 mains. I've got new carb to manifold boots on her with new clamps. It also has a stock airbox setup with stock hardware holding it to the airbox plenum.  I have been able to find that when I lift up on the right side of the carb bank for 3 and 4 the idle drops to where it should be. I'm not sure if I should try to get new carb boots and clamps or what. This has been an ongoing issue for me and I have removed and reinstalled the carbs and tightened clamps to no avail. Any ideas or help is greatly appreciated as we are out of the "CNY Winter" and weather is starting to get nicer.

[calj737]

It’s pretty obvious that your carb boots have either a tear or the manifolds have a leak beneath them. If you’re not using the stock type band clamps around the boots, they too can tear holes in the boots.

[550Resto]

I purchased oem repros for clamps and the boots are NOS I believe. I've inspected them the few times ice had the carbs off and see no tears or rips. Could the carbs be sagging on the right side causing a leak or is this unlikely? Like I mentioned I can lift up underneath the bowls on the right side and the idle comes down to normal.

[BobR]

   Are the intake manifolds tight? Are the orings good? Bob

[550Resto]

Manifolds are tight and orings are new.

[BobR]

 Hmmm...sounds like bases are covered for intake leaks. Could try something to spray around the intake boots and manifolds while its running... Stupid question- by lifting up on the carbs are you maybe affecting the throttle linkage? In other words is the linkage is resting on the stop to begin with? Just grasping at straws...Bob

[550Resto]

Hmmm I did change out the cables with n ee, but couldn't get the top cable on. It was like it was too short, but it should work. I'll attempt to get a picture so I can better explain.

[550Resto]

The top of the cable seems too short and I'm not able to get the end into the throttle holder.

[550Resto]

Looking at the boots that I bought that go from the carbs to manifolds, they look to be repros. I see that the repros are .5mm larger than what the stock OEM boots are. This goes for the Side A and B as well as outer diameter. The overall length in .3mm longer. Would anyone think this could lead to an air leak even though the diameters are a negligible size difference?

[Spanner 1]

If the carb bank 'droops' on the right side ( 3 and 4 ) it may be that the carbs are not all the way into the boots. I have previously had to use a 2x4 to lever the carbs in to the boots all the way. It must be taking air if the idle improves when you lift the carb bank. Check that !

[550Resto]

I am getting to my wits end with this bike. I changed out the carb to manifold boots with genuine boots. The reproduction ones were slightly longer. Everything was put back together and I find that after warm up she still hangs idle wise when I blip the throttle. I haven't checked to see if there is a leak, but I can lift up on the carb bank on the right side when sitting on the bike and the idle comes down to where it should be. Not sure where to go at this point. I'll check for air leaks on that side, using WD-40 should do the trick correct?

[BobR]

I am getting to my wits end with this bike. I changed out the carb to manifold boots with genuine boots. The reproduction ones were slightly longer. Everything was put back together and I find that after warm up she still hangs idle wise when I blip the throttle. I haven't checked to see if there is a leak, but I can lift up on the carb bank on the right side when sitting on the bike and the idle comes down to where it should be. Not sure where to go at this point. I'll check for air leaks on that side, using WD-40 should do the trick correct?

  I have read WD40 is a safer alternative to something more volatile. Have you confirmed (I imagine you have but gotta ask) the idle screw is resting on its stop- that the cable isn't ever so slightly pulling on it? If its not a leak its mechanical, you will find it. Bob

[550Resto]

Would adjusting the IMS screws effect the idle? I've got them at 1 and a half turns out, but read another thread where that helped someone trying to hunt down a high idle?

[johans]

i would take a hard look at the cable(s) again  ( proper part, routing  ect.. ) only because when you physically move the carbs it brings the idle down.

[BobR]

Would adjusting the IMS screws effect the idle? I've got them at 1 and a half turns out, but read another thread where that helped someone trying to hunt down a high idle?

   You can play with them and find out but it doesn't change the fact that if you physically move the carbs the idle changes. Either the linkage is being affected or a vacuum leak is being sealed. You need to eliminate suspects. Perhaps the WD40 will either find or eliminate a vacuum leak as one.  That said, the fact that it hangs after blipping the throttle and can be corrected by lifting up on the carbs makes me suspect a simple mechanical issue as well -cable adjustment, linkage etc. Have you tried physically pushing back on the linkage after it hangs? Bob

[550Resto]

Does this boot look to be on correctly? It was tight fitting on both manifold and carb sides. Want to make sure these are not on backwards. The boot not on the carbs is the way I have them on the carbs.

[Deltarider]

* 20180513_082323-1512x2016.jpg (446.98 kB
IIRC the left side (with that extra rim) needs to face the engine side.

[550Resto]

I've checked for vacuum leaks and found none. I have upped the IMS and brought it out 2 and a half turns from closed with little help to the idle and causing a too rich as heard by popping during revving. Is there an adjustment with the throttle cables that can be done? I notice when I push the throttle closed the idle settles down to where it should be. Cables are motion pro and are not binding and the throttle closed as it should.

[Deltarider]

Cables are motion pro...

Then... are you sure you've got the right ones? Do you have US handlebars or Euro?

[550Resto]

The cable lengths are the same as the ones I pulled off the bike. It's a Canadian bike with what look to be normal handlebars? Not sure what came on them stock.

[BobR]

The top of the cable seems too short and I'm not able to get the end into the throttle holder.

   You aren't getting the slack you need with the cable not properly seated. Either its too short or its routed improperly. Maybe you can reroute it- you don't need much. Bob

[550Resto]

Is there cable adjustment at the throttle grip for the cables? Also I didn't see the adjustment in the manual.

[Deltarider]

Also I didn't see the adjustment in the manual.

If you mean the Owner's manual have a look in p72-74 in: http://www.honda4fun.com/pdf_libretti/500/CB500_550/CB500_550_06.pdf

[BobR]

Is there cable adjustment at the throttle grip for the cables? Also I didn't see the adjustment in the manual.

 My 750 has adjustments on both ends of the cable- I imagine the 550 does too (if thats what you mean). You should be able to adjust a small amount of slack into the upper (pull) cable by using the two adjusters. Same with the lower push cable.  If you cant something is wrong. Wrong cable, or very heavy bends in the routing if its close (to having slack) perhaps.... At any rate you should have about 1/8" free play in the throttle when its adjusted properly. Bob

[przjohn]

Maybe I'm not following the thread well.
What problem do you have:

A. When the throttle is blipped the bike idles high but after a little while comes down to the normal idle.

B. The bike idles high all the time.

Also, have you synched the carbs?