Kubota RTV400Ci Throttle body


A load of gas from 2 old gas cans was placed into the RTV400Ci.  My brother in law, his brother and my brother tried to get it running and the best they could do is to get it to idle.  The RTV400Ci would only idle and when you tried to accelerate it would stall out and the engine would quit. 

When I arrived at the farm the Kubota had been placed into the garage and the seat and rear bed had been removed.  I tired to start the 4 wheel and it would not start.  I connected a battery charger and removed the spark plug to check the gap since it was replaced and part of the previous trouble shooting.  The Sparkplug's gap was correct per the service manual (0.024 to 0.028 in. ).  The spark was good nice and blue hot. 

The fuel tank had been emptied, flushed out and the only fuel filter a screen at the bottom of the hose in the tank was clear from obstruction.  Yes I said that right the only fuel filter.  The RTV400Ci fuel system only uses a simple screen to stop debris from traveling up the line and then being introduced to the fuel injector rail, actually the input to the one and only fuel injector more on that later.

Since the engine would run at low idle allot of things could have been ruled out.  Using the RTV400Ci WORKSHOP MANUAL (WSM) the following are possible causes:

  1. Improper Sparkplug - Check

  2. Damaged Ignition Coil - Replace

  3. Damage Throttle body - Replace

  4. Fixing Governor link - Fix

The governor adjustments were checked per RTV400CI WSM and looked good, the coil was a low probability since fuel was added then the failure,  I removed the throttle body from the Kubota it required the use of a 10mm wrench and needle nose pliers to work off the 2 connectors.  Note:  the throttle body has two places that hold on to wiring harnesses take care and be delicate.  See the photo's below:

I took the throttle body apart and removed the fuel injector the only problem is I had to drill out the screw holding in the fuel injector which was straight forward the I had to use PB Blaster Penetrating oil to get the screw out. I checked the fuel pressure and it was in specification.  I connected up the fuel injector to the wiring an cranked the engine using my breath for pressure and only a drop of fuel came out.

Since time was critical and I had been told the throttle body was expensive 500 bucks I looked on the internet and could not locate the fuel injector by the part number marking on it.   I then made a call the nearest  Kubota dealer asked for the fuel injector and they did not carry it and told me the throttle body and ECU (computer came in a pair at either $1300.00 or $1600.00 dollars) depending on the RTV400Ci VIN number.  Well time ceased to be as critical for the repair (Since it was 1/4 of the cost for a new Kubota of the same class) and the remaining time was spent readying the Kawasaki Mule for backup.  The only problem was the Kubota has homemade equipment to put up and stretch fencing. The unit needs to be running. 

I did check the Kubota RTV400Ci Fuel Pressure it was in specification 34.8 psi. 

You can go on to youtube and search for " Kubota rtv400ci will not start " this should lead you to a video that covers what I did to get it running sometimes it's easier to watch things. 

Since I could not get a new fuel injector (this is still in work) as a last ditch effort I tired to clean out the fuel injector I had since I could physically feel the injector actuating. My first step was to measure the resistance across the relay 2 conductors and they read about 14.6 ohms using my fluke 88 meter.  So the relay that is part of the fuel injector was not burn open or shorted.  This was a good sign.  Using throttle body cleaner I filled up the input side of the injector a few times and then shot a few burst into the injector input to flush out any debris that was free.  Flipping the injector over I sprayed the output nozzle 4 or 5 times till I could see the nozzle tiny holes.

The easy way to introduce cleaner into the injector is to connect the input of the fuel injector to the fuel injector cleaner and then  pressurize the cleaner (pushing of the spray nozzle)  to ensure it would pass through the injector nozzle. I used CRC Throttle body cleaner. You may want to see this on youtube.  Well it worked and i managed to get the injector cleaned out. Here are photos of the injector spraying, the injector and hypodermic test setup,  and throttle body.


I have some FBYCG50 Fuel Injector injectors on order.  My plans are to try and find a salvaged Kubota RTV400Ci throttle body and build up a test solution, or at least come up with a way to do periodic maintenance on my brother in-laws Kubota. More of the story here.FBYCG50 Fuel Injector

Last update 11/22/20.