Kubota B7800 rolls over but won't start

[AdrianD]

Hello,

My Kubota has a brand new battery. Ran the tractor this spring for a few hours doing tilling mostly. When I went to start again, it rolls over but won't start. Pulled out the battery and found it at 80% which I thought strange. I charged it to 100% but this made no difference. Still won't start. I measured voltage across the alternator wire harness (b terminal to e terminal) and measurement was exactly the same across it as compared to the batter (12.53V). So I guess that means the alternator is ok?

I watched this video:

which helped but on my tractor there isn't three terminals on the white plug on the alternator. Just two terminals so I was unsure how I was supposed to measure voltage across that plug?

I checked to see if there was fuel free flowing across my fuel filter and there is. There seems to be a little pump after the filter which I suppose injects the fuel into the engine but I do not know how to check that or if it would be the problem.

I checked the two fuses on the starter (a 50a and a 30a) and both visually looked fine.

Any suggestions? Thanks for the help.

 

[North Idaho Wolfman]

It's not a voltage to starter issue.
It's cranking just not starting.
There are smaller fuses and other fuses that control the OPC and Stop solenoid.
Check all the fuses, and check for corrosion on the blades.

Other common issue in summer is algae in the tank/ lines/ and filters.
If you have that then you will need to treat your fuel.

Then looking at the fuel filter is a poor way to determine if you have good fuel flow.
Pull the filer and clean the housing removing any water.
Reassemble, then pull the line off the side of the filter housing (RED) you should have good flow.
if you do then reassemble and move up to the side of the injection pump and remove the line there (yellow) with the line off crank the tractor, do you have pulses of fuel out of the line?
If you do, reassemble and move on as it's not a fuel delivery issue to the injection pump.

 

[Edke6bnl]

I do not believe you can check the alternator till you get this running for now you may want to do a Load test of the wires going to the starter to check on bad connections. this video will help you

. This is not your issue if I read correctly if it is turning over at normal speed. Then the problem is a fuel issue flow or possibly the fuel shutoff valve. after you get it running start checking the dynamo,

I copied this off the internet
the books are jinglish, and IMO hard to follow.thus I have my own teststhe regulator/rectifier has 6 wires. 2 are the same color, they end up at the dynamo. AC. One is ablack ground wire. You will also have a +12v from the slow-blow fuse, and a +12v ignition (keyon) and then a wire that runs to a charge lamp (if applicable, but it'll still have that wire).Typically loss of charging performance is fairly easy to diagnose if you have the know-how, anda digital volt-ohm meter that has any quality whatsoever. A $10 one isn't that, just somethingelse to throw into file 13 when it reads wrong.The two dynamo wires (usually sky blue) are AC voltage, as said. Start engine, disconnectregulator and test ac output at the regulator connector, between the two dynamo wires. Should be24V+ and I like to see more than 45 or so at full throttle. If it charges anything it's probably ok,they are a foolproof and extremely simple design that rarely fails outside of seized bearings. OK?Move on. Check your ground at the reg connector. One probe of the DVOM (set to ohms) on theground pin in the connector and the other pin on a good ground, frame, transmission, etc. Mustbe clean. If you have more than a few ohms of resistance, your ground or harness is suspectonward. Find your wire that comes from the battery. Backprobe the regulator connector. Nowput your DVOM on DC volts. One probe goes to your connector, the other goes to the battery +.Should be under 500mv, or 0.500v. Ok? Move on. More than 0.5v? You have either a harnessproblem or a bad connection at the fuse, or whatever.Last wire that will affect charging is what I call the "trigger" wire...it turns the reguator "on" soto speak, via the key switch. That one gets 12v when the key is on. Same as the last test,backprobe the connector with the key on. One probe of the DVOM in the connector and the otherto the + battery terminal (use the post not the cable). You want to see less than 0.5v on the meter.If you see more than that, harness, fuse block, keyswitch, etc. Follow your wiring diagram. Ifyou do see less than 0.5v, that circuit is not suspect, and there's a possibity you have a badregulator.Ideally you want to test everything AROUND the regulator because testing the reg itself isn'talways conclusive. Thus, once you know you have AC voltage from the dynamo, you have goodground, you have +12v from the batt and ignition switch, the only component left is the reg.Process of elimination.Electrical diag is not all that hard or it can be. It's all what you make of it. Don't put too muchthought into it because it'll bite you. It's simple for the most partspeaking of being bit, be careful around the dynamo wires when testing. There's a little bit of

 

[AdrianD]

Thanks North Idaho and Ed for the ideas! I will give them a go and report back. Much appreciated!

 

[Edke6bnl]

Let us know what you come up, I also have a B7800.