Kawasaki fuel delivery problem

[Mr Mower Man]

I have a Cub Cadet 3648 Commercial ZTR in the shop (53AB5D4M100) with a Kawasaki FH500V-CS14. Has about 930 hours on it. Guy just bought it, mowed his front yard with it, mowed about half his back yard with it on full choke, and now can't get it to run at all. The mower has 2 gas tanks on it, but he says the one on the left leaks, so he only uses the one on the right. He had fuel line running directly from the right side fuel tank, over top of the engine, to a red pancake fuel filter, then to the fuel pump (which was the wrong pump even though it looked similar), just so he could try to get it running. I ran it with this setup. Couldn't get it to run at all at first. To make a long story short, I rebuilt the carburetor, and then it ran fine...until I configured the fuel line the way it's supposed to be, with new hose and a better fuel filter and the correct fuel pump. The fuel doesn't seem to be pumping very effectively. It will run OK for a little while and then suddenly die. I discovered that it does just fine when I took a small pair of vise grips and clamped shut the fuel line that's coming from the unused left fuel tank (the lines come together to a "T"). I mowed with it for several minutes like that, but when I took the vise grips off, it lasted about 30 seconds and then died.

I wondered if the pump wasn't working too effectively, so I checked the crankcase vacuum with my homemade water manometer, and the engine was pulling about 6" vacuum. I don't know what it's supposed to be, but that seems marginal to me, certainly not an obvious sign of what's wrong. This is a weird problem that I don't recall seeing before. Since the guy doesn't use the left fuel tank anyway, I'm thinking we can just block that side off and it will be fine. But I'd like to know what's causing this issue. Any ideas?

[Gerry]

Just a shot in the dark, is it possible that without the vise grips in place the fuel pump is sucking air from the empty tank and restricting the supply side some way?

[38racing]

Just a shot in the dark, is it possible that without the vise grips in place the fuel pump is sucking air from the empty tank and restricting the supply side some way?

in original setup I assume fuel level equalized in both tanks ie just a larger tank capacity but that makes me wonder if they were just teed why wasn't fuel going from good tank into the leaking tank or are outputs at top of tank. If the latter then your theory makes sense for sure.

[bgsengine]

Just a shot in the dark, is it possible that without the vise grips in place the fuel pump is sucking air from the empty tank and restricting the supply side some way?

in original setup I assume fuel level equalized in both tanks ie just a larger tank capacity but that makes me wonder if they were just teed why wasn't fuel going from good tank into the leaking tank or are outputs at top of tank. If the latter then your theory makes sense for sure.

Some machines had a gated Tee - it'd automatically switch one side to the other based on relative fuel flow.. as one side loses fuel level, head pressure on that side grows weaker until the pressure on the other side overcomes it and fuel starts flowing from the other tank. However, such a set up could easily bleed in air through from one side, ,while at rest, preventing backflow..

However given the issue, I'd do a diagnosis by bypassing that entirely and just hook from one tank straight to fuel pump (or filter). if things work fine then, may be worth testing the tee to see if it has a leak as I mentioned.. worst case, just fix the leaking fuel tank and problem solved perhaps?

[KE4AVB]

Looking at the part it looks like a standard plastic tee so it just let both tanks self balance so that probably why the customer had installed a dedicated fuel to the good tank.