CB1100 Idle speed instability problem

[Magnus_imp]

Good to hear, Dave! What part of San Diego are you in?

Hi Magnus. I am just off the Genesee Avenue exit from 163, near the intersection of Linda Vista Road and Genesee Ave. And you?

Hi Magnus. I am just off the Genesee Avenue exit from 163, near the intersection of Linda Vista Road and Genesee Ave. And you?
Point Loma

[Mechanix_imp]

Update, and something interesting: I've had the bike out the past two evenings (25 miles Wednesday, a lot of stop and go) and about 10 miles last night. So far it is running perfectly!

To my surprise, for the very first time, (at least that I have ever noticed) I discovered that my idle speed increased a very small amount when I was releasing the clutch when the engine was just started and still in the cold/high idle mode. I had to actually stop the bike twice to determine if what I was seeing was real, or imagined. Just at the point where the clutch would begin to engage the RPM increased by less than 200 RPM. I have never noticed this before, but the increase was so slight that it's possible that I just missed it. This is a topic that was brought up (I believe in this thread) a while back, but not much was ever said about it (Ferret commented about it). Ever since the topic first came up I was checking my bike to see if it was happening, and it was not. But like I said, it was such a small change in RPM, and it happened so quickly and almost completely unnoticed, it may have been happening to my bike and I never noticed. Has anybody else noticed that their bike does this also? I wonder if replacing the IACV had anything to do with this?

I know I brought it up a while ago and posted a link to a YouTube video of the cold idle increase. I also have video of the idle rpm decrease during the warm weather riding. I haven’t had the IACV replaced.

Something I have noticed but not quite sure yet if it is just a gap in issues or coincidence. I know I don’t need to run 91 octane fuel but is just a habit from previous bikes and cars, I recently filled up with 87 octane twice and haven’t had any issues...yet. I’ll fill up a third time then switch fuel again to see if I have any changes. I don’t have the time or patience to dig as deep as some of the other guys so I will try to keep tabs on the off the wall things I notice with my bike and share for information, questions or even entertainment.

[dave]

Update: Approximately 200 miles with the new IACV and the bike is running perfectly. I even subjected it to a torture test Friday evening - I rode around down town, stoplight to stoplight, first and second gear only, spending more time idling at stoplights than moving, and no problems. Did some back road and freeway riding Sunday with no problems. It's funny how paranoid I am that the idle problem will return every stoplight I come to, but this is something I will have to overcome.

[the Ferret]

That is awesome news Dave. Impressed with your willingness to dive in and work it out. Fingers crossed for continued perfect running.

[max]

Thanks for the update, is there any oil trying to escape from the valve cover seal or have you got a perfect score there as well Dave?

Very happy for you.

max

[dave]

Thanks Ferret and Max. Not a drop of oil trying to leak out of the valve cover. I used Yamabond gasket sealer, and reused the original gasket.
Guys, I have a minor glitch. I discovered that my fuel tank is not venting properly now. When I refilled the tank there was a vacuum sucking air in when I opened the filler cap. I stopped about 50 miles later, before entering the freeway, to see if my tank needed venting, and it did. When I got home I opened the filler cap and air was sucked in again. I lifted the rear of the fuel tank, and it was difficult to see if the vent hose was being pinched directly beneath the tank. So I disconnected the hose and blew through it easily, so I know it is not pinched anywhere between the fuel tank and where it exits out the bottom. I did my best to reinstall the vent hose to the bottom of the fuel tank and reattach the fuel tank without pinching the hose, but it's impossible to see the hose once you lower the tank into position. Is this rubber hose, attached to the bottom of the fuel tank, the only vent in the tank to prevent the vacuum I am experiencing, or does the fuel cap have a vent also?

[max]

Just checked Dave, both the hose vent and the fuelcap vent on my cb.

So if i blow air into the black rubber hose that is the one next to the blocked off one on the left hand side of the bike just in front of the gear shifter it exits inside the tank, i can hear it because i use a long enough good fitting hose that does not leak.
it also blows slightly out of the fuel cap ( the chrome with the sideways slide key cover, i cannot suck a vacuum with the tank cap closed, it keeps letting air into the tank.

Are you sure you got the right hose because there are two separate ways the tank can vent?

Anybody got a different experience?

[dave]

Hi Max. Thank you so much for taking the time to investigate this! The hose that I inspected for blockage is the one attached to the bottom of the tank, right near where the fuel line attaches. I believe this is the only vent line on the tank, so it must be the same line that you are describing. If you're able to draw air out of this same tube, unrestricted, then that means that your fuel cap is vented, and is operating properly. Because my tank is developing a vacuum as the fuel drains, then this means that my fuel cap is not venting properly, does this make sense? I will look for the tube that you described and see if I can draw air out of it. Thanks again Max
I was just thinking - is there a one-way valve on this vent hose, attached to the bottom of my fuel tank? I was able to blow air out of this tube, but I didn't try sucking any air into this tube - maybe I should try this? My co-worker told me his FJ1300 Yamaha had a valve on the vent line that failed, causing his fuel tank to not vent properly and it would cause the engine to die. I'm leaning towards a malfunctioning fuel cap because of the results of the tests Max performed.

[max]

Check engine light in my mind came on and popgun to the rescue, here is what he found regarding the breather hoses on a bike with evap system installed ( your one? ):

" I looked at the black hose on the bike using an inspection mirror and more in depth in the manual.

The fuel tank breather hose comes from the fuel tank and goes to the EVAP canister. From there it comes out another fitting on the canister and hangs down by the plugged hose.

On one drawing the black hose that hangs down is called the fuel tank breather hose, and on another it is called the Evap Canister Drain hose.

Just for info, there is another hose on the canister--Evap canister to solenoid valve hose."

here is the link for completeness: http://cb1100forum.com/forum/showthread....8#pid87598

So what i think is happening is the fumes from the tank are beiing scavenged by the evap system which is why you get a small vacuum in the tank.
The fuel pump delivers several psi's to the injectors, enough to make a fine mist, so a slight bit of vacuum won't make any difference for the fuelpump delivery.

Bottom line: bike is fine as far as i can see.

max
.

[Lord Popgun]

Max, Dave,

There is a diagram in the service manual of the Evap system along with an small explanation.

I’ll send it to you Max, and you too Dave if you PM me your email address or Phone if you want a text. Give me a little while Max. I just got home.

Just for info since Max mentioned it. Fuel pump pressure is 50PSI at idle for ‘13 and ‘14 bikes. The flow rate is different though.