Topic: my new 3Krpm idle

[Klark Kent]

what would cause a cb550k1 to suddenly start idling at 3000 rpm?
i used to get an intermittent racing idle that has recently become permanent.  the only thing that had happened concurrently was about a twenty degree drop in average temp. from around 70F to 50F.  would an air leak cause this steady fast idle? 
i will be taking the carbs off today to spic and span them, and my engine side carb insulators should show up sometime this afternoon, just wanted some opinions on whether this will fix it, what to pay special attention to, or if there is anything else i should be paying attention to indicated by the fast idle.  I will be outside on my sidewalk wrestling with my carbs as i await your valuable input.

TIA
-KK

[rlarkin70]

that could definitely be an air leak, maybe the cold temps had an effect on a seal somewhere. I think you can check by spraying some carb cleaner around the area where you suspect a leak, and see if the idle drops back down.
it could also be a sticking throttle cable or spring, that kind of thing.

[KB02]

One fine spring day I just couldn't wait any longer and I got my Ducati out of it's winter hibernation and went for a ride. It was brisk. Upper Forties to low Fifties. I had stopped at one point and was talking with a guy at a convenience store about the ride. I told him how well the bike was running (surprisingly well after sitting all winter). He response was, "Well, yeah. Cold compressed air makes for better horse power."

SO, what this stories tries to impart is that, yes, you do have an air leak. And most likely the temp drop you mentioned could, indeed, be having an effect on the running of the bike. Pay close attention to your Carb Mounting rubbers. If they're hard or cracked that could be the cause of your air leak.

[Klark Kent]

Not enough daylight to get the carbs back on yesterday, but they are off and clean.  Looks like I have a minor gas leak at the tee between 1 and 2.  could this be the airleak?  i have new carb mounting rubbers and will install with them, but i am tempted not to address the minor tee leak (waiting for the right o-rings to arrive does not fit in with my schedule) if it isnt likely to be the cause of the fast idle. 
thanks for the help folks

-KK

[tsflstb]

I notice the same thing.  My carbs don't behave like there's an air leak, but the idle does creep up a few hundred RPM when the temperature drops.  I know I'm running rich at idle, so my theory is the cold air makes for a better fuel/air mixture and raises the engine speed.

[edbikerii]

Maybe throttle cables are contracting due to the colder temps?

[HondaMan]

Maybe throttle cables are contracting due to the colder temps?

If the cables have age and an accumulation of crud, they usually stick near their ends-of-travel, more so when cold.

Are your cables old? Can you back-force the throttle and drop the idle down?

[seaweb11]

Cold air =  (more dense) than warm air (less dense) & will change your fuel/air combination you have set up your carbs for nice warm rriding conditions. I do agree though that a leak would be more aperant now in the cold weather.

I notice a difference on my 78K in the cold weather.  MY BIKE LOVES COLD AIR!!!!   It runs way harder in the cold .
probably means I'm running lean??in the summer??


Come on you all you aircraft experts.......?

[Klark Kent]

i can effect the idle in a very minor way by putting all of my might into back-forcing the throttle.  Last year i ran it all winter set up like this and had a fine idle that, as i mentioned, would occasionally race up to 3000.  so i am thinking this was just the last heat cycle of something before that intermittent leak became permanent.  Hopefully that something is one of the carb insulators I have replacements for.

They do love the cold.  Mine does and i know i have it running slightly rich, so I dont think it indicates a lean condition in the summer.  Just a sadistic old scoot.  Running off of your suffering.  no pain no gain. 

I worked all day yesterday and today i leave for NH until the 13th, so the carbs are still inside the house and off the bike.  I guess that gives me time to address the minor fuel leak- from the fuel tee, which is just resulting in a minor coating of fuel on the number two carb and not even dripping.  Should i put in an order for those fuel tee o-rings, likely paying more for the shipping, before I leave or not worry about that until the next time i have to order parts and take the carbs off for a full deracking? it doesnt sound like people think that is contributing to my problem. 

anyway, good luck to all in the winter months, when our bikes run well and cagers stop looking for cycles.  be careful out thar
-KK

[HondaMan]

Cold air =  (more dense) than warm air (less dense) & will change your fuel/air combination you have set up your carbs for nice warm rriding conditions. I do agree though that a leak would be more aperant now in the cold weather.

I notice a difference on my 78K in the cold weather.  MY BIKE LOVES COLD AIR!!!!   It runs way harder in the cold .
probably means I'm running lean??in the summer??


Come on you all you aircraft experts.......?

Sounds more like you're a little rich, maybe 3%-5%. That's about the density change from 80 degrees to 50 degrees.