Kubota 300 Issue

[RogerAS]

All,

I've had a full stop issue with my Kubota 300. It starts and runs just fine. It will run fine for maybe 10 minutes and stumble, from which it may recover and go back up in RPM or it may die. It will refire fairly easily and then run for 30 minutes and repeat the stumble. It's almost like it's losing prime.

Oil level at right point and clean, very little blow by. Compression good and engine rotates smooth with compression release engaged and no clicks or clanks.

I thought it was getting too hot, so I switched to a backup radiator that I know is clean. No change.

I completely cleaned the fuel system from tank to injector (which I broke down and found clean) using carb cleaner and new fuel. New fuel line and filter. I spun the engine with the injector exposed and it sprayed a nice mist of fuel. No change.

My only options seem to be a bad injector pump, working part of the time, or maybe a sticking valve. Any thoughts?

RS

[Westcliffe01]

Fuel tank breather plugged ?

[M61hops]

I agree with Westcliffe01, fuel tank can't breath and injection pump pulls a vacume on it, fuel flow to pump stops.  Or maybe valve lash is too tight, valve stem grows from heat and holds valve open?  How does motor sound, feel right when it stops and will it restart right away or does it need to sit awhile?  Usually turns out to be something simple but weird  !               Leland

[RogerAS]

Thanks for the replies all!

The fuel is fossil off road diesel.

The tank is a 5 gal "Jerry" can about a foot higher than the engine inlet and well vented.

I haven't run the valves yet, but that's a 10 minute job, and there is no excessive noise from the upper end. I do have a spare head that I know is good. I'll just need to get a new head gasket.

Perhaps the exhaust valve is carbon coated on the combustion side, or a guide is worn?

This engine has (had) run for several years in its present configuration without issue. It has less than 5 hours on a oil change and the volume level is right on.

After one of the stalling episodes it will crank right back up, no need to cool down.

If the injection pump is failing could these symptoms be pointing to that?

This started when I began using the engine in slow speed (around 1,000 RPM) mode to assist the solar in keeping the battery bank even when we run the AC. Driving a large frame alternator to about 10 amp @ 12V at a constant rate. I've done this for years with no issues.

I wish it were not so bloody hot so I could work on the engine without sweat blinding me!

Keep the ideas coming guys, 'cause I'm stumped!

RS

[Henry W]

I read through my EA300 shop manual and it also says: Check Fuel return line to make sure it is not plugged. I guess it is possible to build up a small pocket of air on the return side that it could effect operation if it cannot purge small air pockets.

Henry

[RogerAS]

I read through my EA300 shop manual and it also says: Check Fuel return line to make sure it is not plugged. I guess it is possible to build up a small pocket of air on the return side that it could effect operation if it cannot purge small air pockets.

Henry

Henry,

I took the injector completely apart and the return line isn't even attached right now. I could care less if a few spurts of fuel hit the floor at this point. I made sure the entire system is spotless from tank to tip of the injector. I didn't pull the injector pump, and I may do that Sunday morning. I think I can detect obvious wear, but I've not dug this deeply into the timing gear side without having a nice clean bench to spread things out. I need to review the procedure!

I have the shop manual too, and I've spent far too much time with this already. I may load it up in my pickup and take it to a real mechanic next week. I've living off the Honda GX160 turning the alt nice and slow. I use about 2 gallons of gas as opposed to a little over a half gallon of diesel for the same run time for the Kubota. The Honda doesn't seem to mind running under that light load and at low RPM.

RS

[Westcliffe01]

Roger, that is scary stuff.  Cleanliness is a steep requirement for fueling components and usually at home the environment is a disaster.    The pump will most likely have some sort of check valve that the fuel flows through on the suction part of the cycle and then prevents it returning to the tank during the pressurizing part of the cycle.   If this check valve is sticky (possibly due to previous contamination) you could also have a problem.

[RogerAS]

Roger, that is scary stuff.  Cleanliness is a steep requirement for fueling components and usually at home the environment is a disaster.    The pump will most likely have some sort of check valve that the fuel flows through on the suction part of the cycle and then prevents it returning to the tank during the pressurizing part of the cycle.   If this check valve is sticky (possibly due to previous contamination) you could also have a problem.

I think this (pump) is the case. While it is possible that I have a valve that starts hanging when it warms up, messing with combustion, I feel the engine is suffering from some form of fuel starvation. When I ran the engine dry on fuel before, and I failed to bleed the system well, it acted much like this.

I'm not so sure I want to try to take the pump apart. It's one thing to take one off and bolt on another, while a totally different cat to open up one of these delicate little bastards.

I'm seriously considering a total rebuild while/since its down. A new head, sleeve, pistons/rings, rod and lower bearings, cam/lifters/rods, pump and injector and this little engine should last for many years. This engine was used when I bought it four years ago by the US military, and who knows how hard it was abused then. I doubt I can buy an engine anywhere near as cheaply for the quality. buy I would absolutely love to have a GM90, a real one.

RS

[mike90045]

This started when I began using the engine in slow speed (around 1,000 RPM) mode to assist the solar in keeping the battery bank even when we run the AC. Driving a large frame alternator to about 10 amp @ 12V at a constant rate.   I've done this for years with no issues.

Started at low speed usage  - BUT  you've done it for years ??

Carbon loading from light running  ??  Try fogging the raw intake (not the air cleaner) with water mist from a spritz bottle, or one of the other de-carbon methods.

[Apogee]

"the return line isn't even attached right now."

The fuel return line attaches to the pump inlet.  If it's not hooked up, it's likely losing prime and running out of fuel.

Needs to be hooked up.

Other thought that comes to mind is low fuel volume to the pump.  Pull the line off and let it run for a minute or two into a coffee can and see if a) it has good strong flow and b) that it keeps flowing for several minutes that way...  You might need a small helper fuel pump if it's trying to pull fuel from too far away...

Steve

[Lloyd]

Also check to make sure the fuel supply line isn't collapsing...I've seen that happen with the same symptoms...It sounds as if air is in the the suctions side...filter...olive...copper washer...or a cracked fitting...I have seen this happen with the same symptoms.

Lloyd

[RogerAS]

"the return line isn't even attached right now."

The fuel return line attaches to the pump inlet.  If it's not hooked up, it's likely losing prime and running out of fuel.

Needs to be hooked up.

Other thought that comes to mind is low fuel volume to the pump.  Pull the line off and let it run for a minute or two into a coffee can and see if a) it has good strong flow and b) that it keeps flowing for several minutes that way...  You might need a small helper fuel pump if it's trying to pull fuel from too far away...

Steve

Steve, the return line on the 300 is at the injector, and I have been running that off into a one gallon jug instead of returning it to the tank for years.

I have done the flow test and fuel is getting to the pump inlet just fine.

Thanks for the ideas though.

RS

[Henry W]

Hi RS,

This makes sense to me. If the line is just hanging down all the fuel could be running out and air is then working itself to the the pump and or injectors. In order for the fuel system to work properly the return line end needs to be above highest point of the fuel system. And the end needs to be submersed in fuel to prevent air from entering. Here is a good test to do. Get a clear container and and mount a fitting on the bottom and put some fuel in it when it is mounted above the highest part of the fuel system which would be the filter return fitting if you are still using the origional filter and the overflow pipe line coming from the injector. Start the engine up and run it. Let it run for a while than start looking for air bubbles coming from the return line. If you have bubbles than you have an air leak some place.

Oh! I remember that the fuel return line to the bottom of the tank on my EA300 was pitched up the whole way to the tank. even the fitting was verticle. This allows all the air to excape instead of being trapped in the line. And fuel covered the fitting to prevent air working its way in the fuel system.

Another alternative is if you cannot pitch the return line and the fitting up to the tank. Make a loop of the return line above the highest point of the fuel system. this will allow fuel to stay in the line preventing air to enter.

Henry

[RogerAS]

Also check to make sure the fuel supply line isn't collapsing...I've seen that happen with the same symptoms...It sounds as if air is in the the suctions side...filter...olive...copper washer...or a cracked fitting...I have seen this happen with the same symptoms.

Lloyd

Llyod,

You may be on to something here. When I removed the inlet fitting I noticed the copper washer between the inlet fitting and the injector pump was distorted a little bit. I will replace that little devil and give it another try.

Thanks,

RS

[Henry W]

Damaged or loose sealing washers are one of the most important things to look for when inspecting and servicing a fuel system.

Try the test that I wrote earlier once you have checked the sealing washers.

Henry