View Full Version : 28 hp kubota inboard rough vibration

marsh trapper
05-26-2015, 10:34 PM
Hey guys I have a small deadrise workboat with a 4 cylinder kubota diesel that vibrates rough n really bad when throttle is all the way down..if I bump it up it smooths right out and stops vibrating ....what could be causeof this?

David G
05-27-2015, 12:01 AM
I'd say this probably belongs in the Building/Repair section. Might garner more of a response.

05-27-2015, 01:35 AM
Yeah, not here. Here they'll tell you it's running rough because Obama fouled the spark-plugs.

05-27-2015, 05:02 AM
Sounds to me merely too low an idle speed, especially if in gear. Bump your low speed setting while in gear till vibration stops.

Cheers, Dumah

Paul Pless
05-27-2015, 05:50 AM
Obama sucks

05-27-2015, 12:16 PM
Without knowing the specific RPM, engine model, fuel pump type, this is an impossible question to answer.
The short answer is "Don't let it do that". It is hard on the engine. A simple correction with the throttle setting is good short term advice.

It could be timing, fuel quality, a weak governor spring or sticking governor, a bad injector, the engine operating temperature, a failing bearing in the transmision, any combination of these, or just an incorrect low idle setting.

( It sounds like at your low idle speeds the engine is trying to stop, for whatever reason, and the governor is "correcting" that condition, the result being "hunting" between the low idle setting and the "stop" setting.
The correct method for adjusting the low idle speed can be elusive, a professional familiar with the specific engine/pump should be consulted and after a timing check, and if there are no obvious broken parts, he will probably just re-set the low idle speed on the governor. It is often a fractional adjustment between the "stop" setting and the low idle setting, and any of the above mentioned variables can change it.
The terms low "idle", and high "idle" only indicate a "no-load" condition, minimum and maximum allowed rpm.
On a little Kubota, the "high idle" might be as high as 3200 rpm!)

05-27-2015, 01:14 PM
What's it idling at?

05-27-2015, 01:34 PM
Use tax free diesel.

marsh trapper
05-31-2015, 06:45 PM
Its a kubota 28 or otherwise known as a beta28 marine motor idle gauge of course isnt workin right half time ..I feel its idled too low but dont know how to adjust on thi motor ..I read it should be at 900rpm at idle...so next question d I get a kubota rpm gauge or a standard one..max rpm is 3600 for her...oh and it shakes in gear as well until I up the throttle then smooths right out

wizbang 13
05-31-2015, 07:21 PM
Obama may have caused your cutlass bearing to wear a bit.

CK 17
05-31-2015, 07:31 PM
Is there an idle stop? How do the mounts look?

CK 17
05-31-2015, 07:38 PM
Here's a beta 20 manual. I couldn't find a 28 manual but I'm sure there's one online somewhere. The 20 addresses the issue.


CK 17
05-31-2015, 07:48 PM

this one says its for a beta 28, page 15, increase engine tick over speed, whatever that means. . .

Good luck

i found the manual here.


05-31-2015, 08:15 PM
Tickover, Brit for idle.

marsh trapper
06-02-2015, 02:04 PM
Well some closer look at my motor and fou d its a phasor ..does it make any difference