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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.
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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.
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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.
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(05-22-2018, 10:20 AM)Dave_imp Wrote: 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.
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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.
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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.
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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.
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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
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Good work Dave! I knew you would find it. Could really only be one thing-a pinched hose or a misrouted hose. Now ride 
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