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: Oil Drip (from bottom black tube)

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.

 

[dave]

Hi Max and Popgun, thank you for your replies. The vacuum I am seeing in my tank is more that just a tiny pressure differential, I can feel it holding the fuel cap closed. I am concerned I will experience vapor lock at a very inconvenient time (like on the freeway at 70 mph). I am going to look beneath my bike closely for the black, drain tube this evening. I saw the large, clear tube with the blocked-off end near the side stand, but didn't notice the smaller, black tube. In my inspection yesterday I was able to blow freely through the tube after disconnecting it from the bottom of the fuel tank, but I did not try sucking (sorry, I can't think of a better word) on the tube. Neither of you guys mentioned a one-way valve in the drain line, so I assume there is not one. My bike has never experienced this vacuum situation before, and I believe it has something to do with all the parts I removed when I replaced the IACV and inspected the valves. I am hoping that it was just the hose being pinched off right at the bottom of the fuel tank. It's impossible to see exactly what happens to this hose when you lower the fuel tank into position. But I still don't understand why my fuel cap doesn't have a one-way vent built into it. I'll put some miles on the bike tonight and see if the vacuum condition still exists, and report back.

 

[Lord Popgun]

Dave, there is no check valve.

At work, the young guys will say everything was working good until I did this and now it doesn’t work. What do you think is wrong? And we say, whatever you did last!

Personally I think you have a hose on wrong somewhere. You did have a lot of the bike apart. I think the diagrams will help to find the problem.

 

[max]

Here's a thought; if the fuelcap is opened to release the vacuum, closed again and then the engine is started;
how long before the new underpressure has buildt up again?
In other words what role does the engine play in producing this?

Second test; run the engine with the fuelcap open and close the opening with your hand, can you feel the suction increasing?

Sorry dave, i am in guess land here since the evap rules are not part of my bike, but i hear what you say about it not happening previous to the iacv transplant and popgun's suggestion makes more sense than mine.

 

[flynrider]

Hi Max and Popgun, thank you for your replies. The vacuum I am seeing in my tank is more that just a tiny pressure differential, I can feel it holding the fuel cap closed. I am concerned I will experience vapor lock at a very inconvenient time (like on the freeway at 70 mph). I am going to look beneath my bike closely for the black, drain tube this evening. I saw the large, clear tube with the blocked-off end near the side stand, but didn't notice the smaller, black tube. In my inspection yesterday I was able to blow freely through the tube after disconnecting it from the bottom of the fuel tank, but I did not try sucking (sorry, I can't think of a better word) on the tube. Neither of you guys mentioned a one-way valve in the drain line, so I assume there is not one. My bike has never experienced this vacuum situation before, and I believe it has something to do with all the parts I removed when I replaced the IACV and inspected the valves. I am hoping that it was just the hose being pinched off right at the bottom of the fuel tank. It's impossible to see exactly what happens to this hose when you lower the fuel tank into position. But I still don't understand why my fuel cap doesn't have a one-way vent built into it. I'll put some miles on the bike tonight and see if the vacuum condition still exists, and report back.

If left unchecked, one of two things would happen. If the fuel pump got to the point where it could no longer pull fuel from the tank, it would act like it's running out of gas and sputter to a stop. There's another scenario where the fuel pump continues to pull fuel until the vacuum is so great it partially collapses the fuel tank. I've seen this happen on steel aircraft fuel tanks that had a blocked vent. Fuel pumps on injected engines are pretty strong.

 

[Houtman_imp]

Large stainless steel wine tanks will cave in when not vented when bottling, you never get them back to the proper size and loose capacity.

 

[dave]

Thanks for all of your suggestions guys. I haven't looked at the service manual concerning this topic yet, but to my knowledge there is only one vent tube coming out the bottom of my tank. The fact that I can blow air freely through this tube makes me believe this hose is not blocked. Also, I am 100% sure that this tube is the correct tube that attaches to the bottom of the tank, but what I am not 100% sure of is it is not being pinched when I lower and attach the tank. Max has some good ideas, thank you Max, but what I am going to do tonight is disconnect this tube from the bottom of the tank and then go for a ride. If the vacuum issue persists, then I know this hose has nothing to do with it, and the problem is most-likely the fuel cap. I'll post the results of my experiment tomorrow.

 

[the Ferret]

that makes sense Dave

 

[dave]

Hi Guys. I have definitely determined that the breather tube on my bike was pinched closed directly beneath the fuel tank. I probably have the hose incorrectly routed, and I am going to send a picture to Doc for his thoughts (because I have his email address, and I don't know how to upload pictures to this site and it's too late tonight to learn how). I did some tests by blowing air into the fuel tank through the filler cap, and when I disconnected the breather hose air flowed, but when I reattached the hose and lowered the tank air would not flow. I was able to force the hose into a position so that it would not be pinched when I lowered the tank, but I don't think I have the hose routed properly. I think that when I reassembled all of the air box pieces I removed to get at the IACV I should have routed the breather tube differently - I did not remove the breather tube from the bike. If someone could post a picture showing the correct breather tube routing beneath the tank (by lifting the rear of the tank just far enough to see the tube) I would really, really appreciate it.

 

[max]

See, popgun had the right idea.
lifting the tank reveals a channel for the rubber breather hose to live in.


route away from the tank in the channel




another view from the left




the channel for the breather hose on top of the airbox



This picture is taken when the right side cover is removed looking forward with the frame to the right
The hose runs behind the metal plate almost invisible and shown by the red dot in the pic, camera could not see it but runs freely straight down and moves up and down to allow for the rubber hose moving back when the tank is lowered.



and another overview


Hope that helps; max

.

 

[Lord Popgun]

Good work Dave! I knew you would find it. Could really only be one thing-a pinched hose or a misrouted hose. Now ride