HELP! Kubota T1600 looses rpm

I have an older Kubota T1600 hydrostatic trans about a '94 model, under 500 hours.
Earlier this spring I was doing some routine maintenance, changed oil, greased it, and changed the fuel filter by the engine. After I changed the fuel filter I had a hard time getting all of the air out of the line. I cranked on it a few different times, then remembered reading in the manual about if it runs out of diesel you have to do something special to get the air out. I followed the procedure, unscrewing the bleeder screw on the injector pump and leaving the key in the on position until "bubbles" stop coming out, but I never saw any bubbles. I put a little pressure in the fuel tank, and thought I had all the air worked out, but apparently not?
The engine seems to start fine, but then it starts to loose RPM enough that it almost dies. It the "chugs" a little and the RPM's come back up, even in a stopped position. It might do that many times in a row, or it may start to run fine, even at full throttle. I mowed a while with it, then in mid mow, it started loosing RPM's again so I turned the PTO off and throttled it down until it caught up, then it tried to die a few more times, and then ran fine, so I finished mowing.

I already loosened the fuel cap, it didn't seem to help. I don't think its a transmission problem because it ran GREAT before I decided to change the fuel filter
In the 17(ish) years I have operated this mower it has nearly performed flawlessly every time. I had to repair the forward/reverse pedal once long ago, and replaced the belt and idler pulley a couple seasons ago. Other than that I have never had a problem with this mower. Still have the factory rear tires

I remember when I went with my dad to buy this mower, I was around 11 years old, the dealer said my dad's grandchildren would be driving this some day. Last week I let my 7 year old drive it to the barn He was right!

If someone could help me figure out the problem, I would greatly appreciate it!

-Brando

Bulldog said:

Make sure your fuel filter is sealed good. When you change it did you check to make sure the old gasket didn't stick to the base anywhere? I have even seen a entire gasket stick in place during the change. If either of these has happened it would let it suck air in at the filter.

As far as bleeding the air out. Does yours have a small knob that you screw out by hand or does it have a hollow bolt that you have to loosen with a wrench. If it's the bolt it will be right where the fuel line enters the injector pump. If you have this then it needs to be loose and then crank the engine over. As soon as the fuel spurts out cut it off and tighten the bolt up. It should fire right up then. If it has the knob then it needs to be screwed out fully and then crank the engine over until it start. As soon as it starts just tighten the knob up and it should be fine. Doing this has worked every time for me.

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Its just a little 3/8 inline filter. The line clamps are tight. The filter won't fill all the way up with fuel either. It is about 3/4 of the way full. I don't know if that matters.

I have the bolt on the injector pump. I didn't crank the engine while it was loosened. I assumed it would just make more air enter the system. I will try that next!

another thing I tried was elevating the rear of the mower with a full tank of fuel then loosening the bleeder bolt, and lots of diesel came out, but it still wanted to randomly die.

Thanks for the help so far.

squidbilly said:

Hey Brando,
Did you ever figure out this problem. My T1600 (which is just like yours) is doing the very same thing. I already replaced both fuel filters. It runs fine for a hour or two and then it starts acting up like you described. Otherwise, it has been a great mower. Any info. would be greatly appreciated. Thanks.

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Sorry I let this go for so long without replying, I hate when people do that!

Last summer we had a huge drought, I limped along trying to forget about it hoping it would fix its self, well it didnt, lol so this spring I started messing with it again, I opened the little air bleeder valve and injected diesel there with an old syrnge, I ended up getting it to stop shuttering to the point of dying, but now it will mow fine then it looses power greatly, I stop the PTO and it revs back up. I would think there would be a deck problem, but even with the PTO off it doesn't sound right, like it's inconsistent with RPMs.

I gave up and took it to the shop 2 days ago, They are extremely busy so it will be 3-4 weeks before they can get it fixed... I will try and update you when I find out, if i forget PM me and maybe it will alert me with an email.

Fixed!

My lawnmower had a bad electric fuel pump!
I thought it had a mechanical pump this whole time, so it never occurred to me that was the problem... The fuel pump is located behind the battery and up a little.
Maybe someone will read this and find it helpful.