I need help with a 650H that occasionally starts losing power. Enough power loss that it can barely move itself along. The engine sounds normal, even at full rpm, but very little power when put in gear. When this problem first stated, I did all the obvious and checked hydro levels, etc. Even changed the fuel filters, both main and final. And changed the transmission and Hydro Oil filters thinking I had clogged filters. Done this several times, but to no avail each time. HOWEVER, I have since discovered how to get the power back! But that is where and why I need help. The power loss only happens when the fuel tank gets down to about 1/4 full. With a full tank, full power is restored. I need to know WHY it happens and how to fix it. I have noticed several things in all of my trouble shooting. Twice now, when I went to check the mail fuel filter to see if maybe water was my problem, when I opened the drain, (engine not running), I could hear loud gurgling in the filter. Originally I thought the sound was the filter for some reason not getting full from the tank and it was filling up with fuel, but soon discovered it was sucking in air!! Enough air that when I crank it up, the engine soon dies and I have to purge the fuel system of air to get it stated again. Told my dealer about that, and he said my problem was the fuel cap vent was clogged and it was causing a suction. So I cleaned the vent, filled the tank and problem solved!!! So I thought until the tank got low again.
Three things come to mind, Is the pickup tube in the bottom or coming in the top or side? If its pulling from anywhere other than the bottom maybe you have a hole in the tube (inside the tank) at the 1/4 full level or a broken tube Fuel algae in the tank Faulty fuel gauge I would venture to say that the lift pump or main pump has a faulty check valve but I believe the pump is quite a bit lower than the fuel tank ?? Pj
PowerJoke, thanks for the quick reply. Actually, it does have a faulty fuel gauge. Found that out the hard way!! But how would that affect it drawing a vacuum? And I have had experience with Algae in a farm tractor and when it is present, you know it!!! But I have had this system open from one end to the other and have seen no evidence of algae. Not being familiar with the "lift Pump", I would like to learn more about that. And from what I can tell, the pickup tube is in the bottom.
I think you have a screen inside the tank that is plugged up with garbage, it works ok with the tank full but when the level gets low it sucks harder and collapses the screen, and you transfer pump gets starved for fuel and so does the rest of your engine. My old backhoe did this way more times than I'm willing to admit, until I fixed it good enough. Look at the fitting that the shut off valve on the bottom of the fuel tank screws into, if it's a big hex head that screws out itself, then drain the tank and remove it, and look at the screen. Or you could wait till it does this again, and run the fuel inlet from the tank into a temporary tank, prime it up, and see if it runs fine. If you study your primer lever on the transfer pump you can tell the difference between the feel of the lever when it's pumping, sucking but not getting nothing, pumped up and holding, and pumping air. But the filter sucking air already says you have a fuel blockage before that point. On second thought, you may have a bad lift pump, or a blockage, or collapsing hose, anywhere from the lift pump back. Just cause it's doing the same thing doesn't mean it's the same problem.
Your fuel cap has a vent on it. It gets plugged with dirt.