05-22-2018, 01:29 PM
(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.