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Kubota Tractor Won’t Rev Up: Top Causes and How to Fix Them

Kubota Tractor Won’t Rev Up: Top Causes and How to Fix Them

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Paul Brown

Kubota tractors are some of the most reliable compact tractors on the market. But as with any piece of machinery, eventually, something will break which can impact performance.

If your Kubota tractor won’t rev up, it’s most likely due to a fuel consumption issue. Whether it’s water in the fuel tank, the fuel filter, or just bad fuel, the reason your tractor won’t rev is because it’s not able to produce the power it needs to run efficiently.

Kubota tractors have been in production since the late 1800s. In fact, the company revolutionized farming culture and has been developing oil-based motors for agricultural equipment since the early 1900s. They are almost rock-solid. Almost.

Let’s dig into the most common issues that cause a Kubota tractor to not rev up and how you can fix them. 

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Check for Water in the Fuel Tank

Because subcompact Kubota model tractors (B and BX Series) don’t have water separators within their fuel system, water can get into the fuel tank and mix with the diesel fuel inside of it

This can happen for several reasons, but the most common is that the fuel tank was left without enough fuel in the tank at the end of the season, and condensation formed over the winter.

It’s also possible that the head gasket was loose or water could have seeped in through a vertical exhaust pipe that was left uncovered.

Your tractor needs a steady source of fuel to run properly and when water mixes in with diesel it can cause your engine to sputter, lose power and even stall out completely.

This is because water prevents the fuel in an internal combustion engine from doing just that – combusting! This is the chemical reaction that occurs inside an engine that turns fuel into a power source

If left unchecked, water inside a fuel tank can cause bacteria to grow, resulting in a sludge that can severely impact your engine. This sludge will pump through your engine and gunk up your fuel pump, causing a much more costly issue. 

How to Remove Water From Your Fuel Tank

Follow these steps to check and remove water from your fuel tank.

  1. Extract a bit of fuel from the tank. Place the fuel in a clean, clear glass. Set the glass in a cool, dark place for approximately 12-24 hours. If you return to the glass and you can see a clear separation of fuel floating at the top, that means there is water in your tank. 
  1. If there is water in the fuel, bleed it out. You can do this by releasing the valve next to the fuel injector. This is a very helpful video tutorial from YouTube.
  1. Treat the fuel with a cleansing additive. Refill your fuel tank and add a diesel engine cleaner, such as Clear-Diesel, which will remove any microbes and bacteria that may have been built up as a result of the water.
    A small amount of this additive will do the trick, approximately 1/4 ounce per gallon. 

Maybe it’s Just Bad Fuel

If you checked your fuel and there was no presence of water, you could just have a bad batch of diesel in the tractor that needs to be replaced. “Bad” diesel fuel means that there are sediments or other materials present in the fuel that impact the efficiency in which the engine burns it. 

tractor won't rev up? Check the fuel!

The presence of sediment in diesel fuel can happen for several reasons. Maybe the fuel was left out during the off-season and dirt got into the container. Or, maybe the cap was not tight enough and air mixed in with the fuel, causing it to gum up over time. 

How to Check for Dirty Fuel

Whatever the case, there are ways you can check your Fuel for things besides just water. 

  1. Pull a Sample. Much like when checking for water in your fuel, you’ll want to pull a sample and set it in a clear container. 
  2. Check the consistency and color. If the fuel seems thick or is very dark in color, you likely have some unsavory stuff inside. 
  3. Check the fuel filter. If the filter looks dirty, or if upon removal of the filter you find sludge or dirt residue, the fuel is likely dirty. 
  4. Add a fuel cleaner. Much like when treating your fuel for water, you’ll want to add an engine and fuel cleaner to help remove any unsavory materials. 

Check the Fuel Filter

Once you’ve checked your fuel – whether it had water or sludge in it or not, you’ll want to check the fuel filter as well. If there was something unsavory in the tank, there could be sediment and slime stuck in the fuel filter as a result, which will likely require replacement.

Alternatively, if you checked your fuel and there was no water, you’re likely still having the same issues you were having before. 

If the fuel filter is not clear, the diesel fuel will have a harder time getting to the engine, making the tractor work harder than it needs to. This should be a part of your normal maintenance routine anyway.

According to the Kubota Maintenance Schedule, you should replace the fuel filter every 200 hours. 

How to Replace the Fuel Filter

The fuel filter is a plastic cylinder that can be found on the underside of your Kubota tractor, next to the metal fuel pump. Follow these instructions to replace it: 

  1. Restrict air and fuel supply to the filter. Lightly pinch the line with vice grips between the fuel pump and the fuel filter, as well as the line on the other side of the fuel filter. 
  1. Move the metal clamps on either side of the filter. This will allow you to slide the lines away from it. 
  1. Remove the hose from one end of the filter. Pro Tip!: Use a drain pan to catch any fluid that may come out as you do this. 
  1. Loosen the bolt on the filter bracket. You don’t need to loosen this all the way, just enough to allow the filter to slide out. 
  1. Remove the hose from the other end of the filter. You should now be able to remove the filter completely. 
  1. Replace the filter. Be sure to put it in the same way it came out. There are arrows that indicate the fuel flow, follow those. 
  1. Reattach the lines to the new filter. Attach the lines onto the new filter, replace and tighten the clamp, and the bolt on the filter bracket. 
  1. Remove the vice grips from either side of the filter. Be sure to check the lines to verify you didn’t crimp them in the process. 
  1. Test the engine! You may have air in the line as a result of the replacement, so try starting the tractor and revving the engine a few times until it starts up cleanly. 

If you’re unsure about the directions above, you can watch this very helpful video. This guy does an excellent job of walking you through it.

Kubota Fuel Filter Change - EASY JOB - Cheap


To summarize, the most common culprit when you’re dealing with a tractor that won’t rev up is fuel issues. 

Most commonly, the fuel either has water or dirt in it, which can cause the engine and fuel system to become unstable, rendering it unable to turn the fuel into power efficiently.

This can cause issues with the fuel filter, which has to work harder to filter out more impurities than it would with clean fuel. 

To determine if you have a fuel issue, follow these steps: 

  • Check the fuel for water or impurities by pulling a small sample and observing how it changes over time. If it’s off in color or the fuel has risen to the top of the sample, you have an issue. 
  • Check and replace the fuel filter if there is the presence of unsavory fuel, or if you find that there is dirt or sludge present. 

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