I recently purchased a 1991 310c backhoe. I serviced it before I began using it (oil, filter, air filters, fuel filter, reverser fluid/filter). The issue I am having with it after a few hours of use is that it seems to be going back to the idle rpm no matter where I have the throttle lever or foot pedal. For example if I am driving it I can have the foot pedal at wide open throttle going along fine, then suddenly the tractor will start slowing down and be moving at idle speed. After a few moments it will slowly pick the rpms back up and be at WOT again. Any ideas on where I can start checking for what is causing this issue? The tractor had a full tank of fuel when I bought it and its finally down to a 1/4 of a tank. I'm wondering if maybe I should drain the rest of the fuel and put fresh in. Any help or ideas is greatly appreciated!
Yes, drain the fuel. You can always let the crud settle and pour it right back into the tank. Do you have a petcock on the bottom of the tank that you drain off before you start it up (like the manual says!)? Also take the inlet fitting out of the bottom of the tank. Remove the small diameter hose that goes to the transfer pump and take out the screen that's in there, get a new one, clean it, or remove it altogether and use a larger diameter pipe/hose to a spin on filter housing with any oil or fuel filter to trap the big garbage before it plugs up the smaller lines. That's assuming you have a fuel blockage in the tank. The easy way to confirm that is to either tee a vacuum gauge into the suction line, or if the machine will die doing this, immediately hop off and crack the suction line open to see if you hear a hiss. Or if you shut the engine off when it slows down like this and see what the transfer/primer pump feels like. The pump will have hard resistance only when it is pumping (and you won't feel the lever spring back because the diaphragm is using the force to pump the fuel). Also if the resistance is only part of the stroke, the pressure is building, or the fuel is flowing but partly blocked. When it is pumped up and holding pressure, the diaphragm is held away from the lever and the lever is relatively easy to move (back and forth with the same spring force). If the lever moves up/in with medium force AND you feel the same force pushing it on the back stroke then it's sucking air/pulling a vacuum, (the more force the stronger the vacuum). In your case, before you start, open the bleeder on the filter and pump the transfer pump and see how much fuel shoots out. Run it till it slows down, shut it off, open the bleeder and I bet it will only dribble fuel when you pump it.
Ok I will look and see if I have the petcock on the bottom. I am going to go ahead and drain it and clean the screen because im not sure how long the fuel has been in the tractor. Thanks for the info!!