Engine shaking

[RayK]

I have a G1700 Diesel, lately the engine shakes badly, I think its fuel so I changed both filters and it ran better for about an hour now were back to the shake. It seems to get worse as the tank gets low on fuel, I have used additive for water etc and can't see any dirt in the tank. Any ideas would be appreciated.

 

[locknut]

Vent on the fuel cap clogged up?

 

[whistlepig]

Probably sucking air in to a fuel line. Clean the motor thoroughly and dry it. Any place you see fuel leaking will be sucking air also.

 

[hr3]

You might check for a second filter.. My G1800 has 2 of them maybe yours does too..

 

[RayK]

Thanks Guys, I will try your suggestions I was thinking it could be sucking air but I can't see any fuel leaking. I did change both filters. could it be a weak fuel pump?

 

[jinman]

Ray, I would first check that the motor mounts are not loosening. If those are okay, then the Kubota Maintenance Manual says to check the following:

- Fuel filter clogged
- Air cleaner clogged
- Loose/leaking fuel connection to injectors
- Injector nozzle stuck/clogging
- Injector pump defective
- Fuel overflow pipe clogged (I think this is fuel return from the injectors)
- Governor defective

I would make sure all filters are good including the air filter and then look for leaks. If no leaks and you are sure fuel delivery is good up to the injectors, you might remove your injectors for inspection.

 

[grsthegreat]

does this happen AFTER blades are engaged, or while blades are not moving????

 

[RayK]

It shakes all the time,under power or not, it will run smooth for a couple of seconds then begin to shake badly then smoth out again, All the filters are good, guess injectors will be the next thing. thanks Ray

 

[jinman]

It shakes all the time,under power or not, it will run smooth for a couple of seconds then begin to shake badly then smoth out again, All the filters are good, guess injectors will be the next thing. thanks Ray

Ray, my G1800 does the same thing unless I keep the tank almost full of fuel. I think there may be intermittent power to the fuel pump. When I turn on the ignition, I can hear the fuel pump running, but when the engine is running and there is vibration from mowing, the fuel pump could be cutting out and I'd never know it. I just think what you are describing is a common problem with several models of Kubota Lawn Tractors that share similar designs. When the engine shakes and shudders, does it also lose rpm and power? Making sure both fuel filters are new and maybe checking to see the fuel pump is working by opening the outlet side and powering it up would be a good troubleshooting method. If you do that, you must hook up the pump again and bleed off all air at the outlet of the 2nd filter by the engine so that you don't send a slug of air to your injector pump. If that happens, you'll have to bleed air at the injectors to get the engine going again.

 

[RayK]

I blew the fuel injector return lines out back to the tank, now it seems to be running smother but it's low on power, also I noticed after starting it was puffing black smoke and I had very slow throttle response initially then it picked up rpm. Also should the electric pump run continually with ignition on and engine stopped, mine does now, seems before it would run until pressure built up and then stop, but I can't be sure of this.

 

[jinman]

Also should the electric pump run continually with ignition on and engine stopped, mine does now, seems before it would run until pressure built up and then stop, but I can't be sure of this.

I believe it runs continually. I stop my G1800 with a kill knob instead of using the kill solenoid. The last time I used the mower, I killed the engine and sat listening to the fuel pump running for awhile. I'm sure fuel pressure was up, but the pump was just ticking away. I know many old gasoline electric fuel pumps would pump up pressure and quit, but I believe our little solenoid actuated pump runs continuosly with the key on. The manual says it is powered anytime the key switch is ON, but doesn't say anything about stopping when pressure builds.

 

[RayK]

Update, found the problem, the engine to transmision drive shaft front U joint seized causing the splined adapter to wear to the point where it was jammed on the drive shaft at an angle. I had greased the splines regularly, so if you have a vibration problem check this drive shaft. Thanks for all the advice, Ray

 

[jinman]

Glad you found the problem Ray.:thumbsup: I believe that the u-joints on that shaft don't have grease zerks. It has been the subject of several posts on these tractors on this and other websites. I think most of the posts I've read say you have to replace the whole shaft and it's not an easy job because of the amount of disassembly required and tight spaces.

 

[J_J]

I had a similar problem, and found the fuel line from the tank to the fuel filter was clogging up. Tried to blow out the line a couple of times, but suspect that the crud is filling/settling in the fuel line and decreasing fuel flow to the filter and pump. I now have a temporary hose in the top of the tank to the fuel filter, and the tractor runs good.

 

[Kubota3710]

I second RayK checking the u-joints on the PTO shaft.

I have been chasing a vibration problem on my G1800 with 900 hours for a while. I was chasing it on the engine, and couldn't make it get better. It was slowly degrading. I finally found the issue on the front u-joint on the HST PTO shaft. You can reach up under the tractor from the right side and shake the PTO shaft with the mower deck on. Comes out back of engine and goes back to HST which is at rear axle.


Had to pull the fender and steering column off to get easy access, but really only takes about 45 minutes. And allows a lot of clean up around the fuel tank and wire harness. That an a new belt on the mower deck, and my G1800 is smooth as new again.

I have included a picture of the convertible. PTO is readily available in this condition. And I also changed the fan belt when I was in there, as the PTO has to be unhooked to do that. And it was in bad shape after 900 hours.

I have read others do it without removing the fender and steering shaft. I could barely clear it to get it off from above and wouldn't want to tackle it from below. Anyway, well worth the time to get rid of that vibration.