F3680 rpm raising by itself

Tractordoctor

New member

Equipment
New Holland t2310
Sep 12, 2021
16
6
3
Green-pointe N-B
Hi,been working on Kubota for close to 11 year and I’ve got a f3680 in the shop that got me stumped… as soon you start it it will start to rev up slowly until it’s overrevving if I hold the remote on relief it slow down and stay there but as soon I let go of the remote it climb again. The start spring and governor spring are ok I compare them with new one. It’s not the throttle cable as it’s disconnected. The fuel rack is moving freely I also remove the throttle cover with 4 bolt and ran it like that and it’s still doing it It’s not smoking or knocking etc.. I never heard of a governor problem on those engine,but I haven’t seen everything.
 

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,807
1,575
113
Mid, South, USA
on something like this you have to look at all of the possibilities.

The rack controls the plungers, which ultimately controls engine speed-as you already know.

Possiblites are fork issue, governor issue, spring issue, or perhaps even a pump issue

generally a pump issue is ruled out if the stop lever works like it's supposed to, IOW, the engine shuts completely off in a few seconds at the most. If it slowly dies off when the stop lever is moved to the stop position, you'll have to look at why-maybe the rack isn't as free as it should be at the far end of it's travel? Could the rack pin be bent a little? Possibly from an amateur install? Wouldn't be the first time I've seen that. Also, look really close at the delivery valves on the pump. A lot of them have a hex on the delivery valves and when people go to bleed the fuel system after running it outta fuel, they'll "crack the lines"--but at the pump end rather than the injector end. In doing so, sometimes the delivery valve will turn and when it does it can damage the pump. Worth looking at. Generally the governors work or they don't and if they don't you'll find parts laying in the pan, which usually means other bigger problems. Maybe run a small fish magnet down into the pan through the dipstick hole? If that's possible on that unit-I can't remember if it is or not. If not, cut the filter open and inspect. The governor itself is pretty simple in design, but with that being said, if there's evidence of someone tampering with the front cover, maybe the engine's been apart and at that point there's no telling what you'll find. Maybe it's the wrong governor, I've run into one in the past with a different set of issues where the engine came off of a generator and the user had to swap the governor parts from the tractor to the gen engine and in doing so they screwed up a bunch of stuff. As I said, amateurs. These things aren't briggs engines, they're much more complex and sometimes "diesel mechanics" that have little to no experience with Kubota get lost with them. Understandable. Give me a 3208 Cat and I'll be there a while; but give me a D722? Love them!

Another possibility that comes to mind is fuel. I"ve seen diesel contaminated with "other" fuels mixed in cause this but usually they won't shut down.

Another? Diesels will run on their own lube oil. So if your engine has a lot of blowby, there is possibility that it's running on it's on oil coming into the intake through the crankcase vent, if it has one. Some have a road draft tube down the side of the block and that setup would eliminate this runaway possibility. BUT if the engine has any type of fuel in the crankcase, it wouldn't take much to cause a runaway, particularly if the valve seals are worn or if the cylinders are worn. What about the head itself? Any way that lube oil could be dripping into the intake ports? Pull the valve cover and have a look if you haven't already. Check the clearance while it's off, if you haven't already.

can you take the fill tube off or inspection plate off the side and then start the engine? If you can, can you move the rack manually with an insturment and will it vary the engine speed? Maybe you can see something in there while it's running. Rack pin rattling around in the fork, or whatever. That is, if you ain't already done that.

all else fails you may give tech support a ring and see what they have to say. Most of those guys are new now, but there's still a couple old guys that cut their teeth on these old dinosaurs. My issue was always getting through to them...but I had another contact at the time, which is no longer. Unfortunately. Sure did miss him the last couple years I worked at the dealer, great guy--had the absolute best communication skills of any person I've ever dealt with. If you are in the southern region and been around much, maybe you remember Haggerty?