Still not running correctly but have not done what CiscoRanger has suggested. Time is not allowing me to yet, but soon. Have to get through planting and beekeeping startup season first. It seems that the warmer it gets and worse it backfires. Sometimes it seems when I hit a hard bump it backfires but not always. What a pain.
Kubota 400 ci backfire issue
- Thread starter Rollo
- Start date
Hey Rolio. Before you go tearing into to try and clean the valves and such I’d still recommend compression checking it. Go get a loan-a-tool from compression tester from one of the auto parts stores. If it checks good there’s a lot of things you can cross off the list as possible issues And save you from disassembly. Rings, valves, etc.
also an easy check is spark plug tester. To see if you have good spark. Sometimes the connections in the boots or coils to the plug get vibrated loose so you aren’t making good connection to the plug. Spark plug testers are cheap.
Good luck.
QUESTION: Is there a fuel-injector for each cylinder? .... or ONE injector serving BOTH cylinders?
If there is only a single injector for BOTH sides.... then it is NOT a fuel-injection problem....and likely an ignition issue
Black sparkplug suggests running rich on that side (or that plug not firing every time)
Try swapping the ignition-coils between sides, install fresh plugs... and see if the "black plug" stays on same cylinder or moves to other side.
If there is only a single injector for BOTH sides.... then it is NOT a fuel-injection problem....and likely an ignition issue
Black sparkplug suggests running rich on that side (or that plug not firing every time)
Try swapping the ignition-coils between sides, install fresh plugs... and see if the "black plug" stays on same cylinder or moves to other side.
- Stays on same side = NOT ignition coil issue
- Moves to other side = Ignition coil problem.
- replace bad coil
Bruce it is a single cylinder. What fuel pressure and cylinder pressure numbers should I be getting?
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a compression test is inconclusive as the engine has an auto decompressor built into it. This reduces cranking compression by holding a valve open at cranking RPM which eases the load on the starter and such. So a worn out engine might have 90 psi, but a perfectly running engine will also have, 90 psi.
There were some issues with the decompressor on those engines though.
There were some issues with the decompressor on those engines though.
I really thought we were working with fuel-injected Kawasaki Vtwin. (I have worked on these in the past)
Now I realize we are looking at a KUBOTA single-cilinder gasoline engine... To be honest, out of the 100s of engines I have worked on ... never have I seen a KUBOTA brand gasoline engine.
UPDATE: I have looked up the engine-specs here https://www.atv.com/specs/kubota/ut...i/realtree--hardwoods--camouflage/detail.html
This says it is a 2-stroke with OverHead Valves... THIS DOES NOT COMPUTE!!! (a 2-stroke engine does not have OverHead Valves)
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I can tell you that fuel-injection on a small engine can work very well.... until it fails.
It is not always easy to troubleshoot and diagnose.
A rich-running, carbureted engine is trivial to isolate the problem. I have seen many a fuel-injected engine converted to carbburetor due to problems.
Basic diagnosis steps:
- Inspect for vacuum-leaks in the intake plenum.
- Measure voltage at O2 sensor.
- they all work on the same principals so voltage-readings are nothing special
- Without the 'closed loop' feedback, the computer cannot inject proper fuel-mixture
- Make sure all the power/ground connections to the 'computer' are present and accounted for.
- Do not forget that weak-spark can cause black spark plug too.
What octane gas are using? I know that Can-am (Rotex) motors will run the same way if a Hi-octane gas is used. Go figure.
I thought it was an off shoot of the EX40 short stroke, 89mm bore x 65mm stroke, engine.
Information is hard to come by with this model. I have tried, 87, 90 recreational gas and also both with stp and also with sea foam. I am going to check for vacuum issue and gas pressure, just bought the tools. Below is a list of the parts for the model. I surely hope it is not an fuel pump. Might cost a million dollars if one can even be found. lol I found a couple and they are expensive. But I am going to do a thorough test on the one I have tomorrow.
Kubota RTV400CI-A/H (Orange model ATV/HDWS) Parts Diagrams (messicks.com)
Kubota RTV400CI-A/H (Orange model ATV/HDWS) Parts Diagrams (messicks.com)
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This is fuel pressure running video. With another gauge I was getting about 30-35 psi. Had the same reading with both fuel pressure and out of the OHV.
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This one is vacuum running full blast. This is hooked to the vaccum line from the OHC to the airbox
Or the breather line.
Or the breather line.
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none of the video links seem to be working for me, but from the picture 35 psi should be fine based on the video that said 34.8 was factory spec. I can’t find a service manual for this thing. Did you pull the injector yet to see if it was spraying in a nice pattern or gummed up (as in the video)
also I didn’t quite understand your pressure test at the ohc breather line (broken vid link) . You’re running constant 35 psi between the cover and the air box?
Yes, but I did notice that is kind of pulsated also after getting it to operational temp.
No on taking the injector apart.
My videos are on facebook so if not subscribed or opened maybe that is why.
youtube.com
No on taking the injector apart.
My videos are on facebook so if not subscribed or opened maybe that is why.
Kubota 400ci backfiring
Having an issue with backfiring. Hooked up tester to the vaccum from the OHV.
youtube.com
just to clarify, is your gauge tee’d in between the the cover and air box and just measuring as it goes by, or is a straight connection to the cover, dead headed with no outlet to the air box?Yes, but I did notice that is kind of pulsated also after getting it to operational temp.
No on taking the injector apart.
My videos are on facebook so if not subscribed or opened maybe that is why.
Kubota 400ci backfiring
Having an issue with backfiring. Hooked up tester to the vaccum from the OHV.
Also, what did the pulsing measurement look like? Like between 10 35psi, or between vacuum and pressure, or what?
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The boss is making me run some honey-do's here in a bit so here's a few thoughts.
1) your OHC pressure - From the parts diagram, I dont see a pcv valve, so youre crackcase is supposed to have an open connection to the airbox. Make sure you have an outlet during your test. Tee it in to the airbox, dont deadhead it to the gauge. Normally youd test that by connecting the gauge to the dipstick tube, but looks like you have a push in dipstick. 35 psi of constant blowby even deadheaded seems excessive to me, and I'm surprised your airbox neck isnt full of oil or blowing the dipstick out.
2) When it warmed up and started pulsing, what was the needle on the gauge pulsing between?
3) from your video it sounds like rpms get up, then boggs, then up, then boggs. Did you tee in your pressure gauge to your fuel pump and run it under load (like your OHC pressure test)to see if when it is bogging, the fuel pressure is dropping or stays constant?
1) your OHC pressure - From the parts diagram, I dont see a pcv valve, so youre crackcase is supposed to have an open connection to the airbox. Make sure you have an outlet during your test. Tee it in to the airbox, dont deadhead it to the gauge. Normally youd test that by connecting the gauge to the dipstick tube, but looks like you have a push in dipstick. 35 psi of constant blowby even deadheaded seems excessive to me, and I'm surprised your airbox neck isnt full of oil or blowing the dipstick out.
2) When it warmed up and started pulsing, what was the needle on the gauge pulsing between?
3) from your video it sounds like rpms get up, then boggs, then up, then boggs. Did you tee in your pressure gauge to your fuel pump and run it under load (like your OHC pressure test)to see if when it is bogging, the fuel pressure is dropping or stays constant?