BX25 stops running at high RPMs

[yawning dog]

Hello folks, I'm really hoping someone can point me in the right direction as I'm pretty new to diesel engines. I bought a "fixer" BX25 thinking, "how bad could it be". Idiot me. It has several problems, but the biggest seems to be that at high RPMs the tractor seems to start missing, rapidly lose RPMs, shudders like hell and then dies. I've only had the tractor a couple weeks and it seems to do this also under load too, which I'm guessing is coincident with needing to run the engine faster.

My first thought was to change both fuel filters, which I did. Then I changed the fuel pump. There was no apparent effect from the new filters but the fuel pump might have helped. I'm not sure what else to try other than to see if there's a good flow of diesel from the tank. The other consideration is old/bad diesel but I'm not sure if that's as much a concern as with a two-cycle or regular gas engine?

Anyone experienced this?

 

[85Hokie]

Have you checked the air filter?

Run the machine with the fuel tank top off and see if that makes any difference.

IF filter is clean - then the fun part comes into play, a restriction in the fuel line via the tank.

The BX's have known to have rust problems OF the sending unit that is INSIDE the fuel tank - the rust falls and swims around until it gets near the bib to exit - thus clogging up the works. Usually this will choke the engine out at low RPM too.


Easy way to check for restriction - aint fun at all however - pull the fuel line off near before the filter at the tank and with a large glass jar, allow it to flow into jar........ should be a steady rate - if it slows down, you found your problem.

 

[yawning dog]

Hi 85Hokie, thanks for your response! Yes, I changed the air filter too.

Good suggestions, I've thought about the fuel cap thing (I guess possibly a clogged vent creating a vacuum and restricting flow?) but I forgot to see if that makes a difference. I'll also check the fuel flow from the tank like you suggest. Thanks again!

 

[yawning dog]

Hello again! Success, I think! First, let me again thank you, 85Hokie, for your quick response. This issue had me kind of worked up.

The first thing I found was that the gas cap was not on tight so it couldn't have been that as the issue. It still might have a venting problem but that didn't seem to be the cause of the engine stopping.

So next I disconnected the fuel line from the filter coming directly from the tank. I expected to see a stream of fuel, a dribble, or a combination of both as you suggested. Nothing. Not even a drop came out. So next I took the gas cap off and blew compressed air through the fuel line back toward the tank. That gave me a whole stream of fuel when I removed the air. So after getting thoroughly drenched in diesel, I hooked it all back up and ran it around the yard for several minutes without a problem. I'm kind of surprised it ran at all prior to doing this.

It sounds like this might be a common issue? Are there suggestions to permanently correct it or do I have to replace the whole fuel tank? I'm assuming that the rust/gunk that was clogging the tank outlet will eventually clog it again if I don't do something. I guess my question now is whether this indicates something is damaged in the fuel tank.

 

[whitetiger]

If you do not address the restriction, it will happen again.

You need to remove the fuel tank to flush/wash it out into a clean white bucket to see what is in it. It may be rust from the fuel level sender but that is only a small percentage of the early BX series.
I usually find grass or insects in the tank, sometimes plastic pieces. You can get a tea strainer that fits snuggly in the fill neck to keep debris out.

Drain the fuel out, remove the tank, wash it out with soap and water, flush it, and dump it several times. Blow out the outlet filling, set the tank aside to dry, then reinstall it.

You will want to inspect the sender while the tank is out and replace it if it is rusting. The replacement sender is coated differently so they will not rust.

 

[yawning dog]

Thank you, whitetiger, it sounds like a good idea. I haven't looked at how difficult it might be to get to the fuel tank but it seems like it might not be too bad.

On a related topic, it seems that it idles a little rough below about 1600 RPMs. Is there anything that can be serviced or cleaned that would smooth out the idle?

 

[85Hokie]

The idle IS ROUGH at that RPM ......... aint no nice idle about it. Place milk and chocolate in a bottle and it will shake it for you.

At ABOUT 1800 it is a nice smooth machine.

As it idles now - does it seem rough or rather it wants to cut off?

 

[yawning dog]

Chocolate milk... delicious. Yea, I would say "rough". The engine is a little shaky on its rubber mounts and that rattles the hell out of the metal hood which makes all sorts of racket That said, I don't have the plastic wrap around side on or the vertical battery cover thing so maybe by putting all that the orange parts won't shake too much. Any idea what the lowest idle RPM should be when you throttle all the way down?

 

[Henro]

When you turn off the engine, you probably get the “death rattle” too. Just the way it is with a BX.

Does your tractor have a mid mounted mower? If so, one thing I learned after about 15 or 17 years of ownership, is that it’s better to increase engine rpm a bit before you engage the PTO for the mower deck. If engaged at very low engine rpm, engagement is sudden and disturbing, at least in my mind. Much smoother engagement if you pick up the engine rpm a bit.

 

[yawning dog]

Yea, that's a pretty good description. I have a B21 that turns off a with a little more finesse. The BX25 definitely shudders to a halt. No on the mid-mounted mower, but thanks for the tip in case I ever run across one. On the topic of stopping the tractor, I have another bizaare issue that is probaly a consequence of the previous owner's poor wiring choices. There's lots of creative re-wiring on it. But I've found that when the stop solenoid is hooked up, the tractor shuts off as soon as the PTO is engaged or it's being moved as though someone's not in the seat. But if the stop solenoid is unhooked, then all works fine (other than being able to stop the tractor without bending down and manually pushing that little stop solenoid lever). It's really bizaare. I'll probably make another thread about this in case someone might have run across it. I really need an electrical schematic but haven't gotten around to buying a WSM yet.

 

[whitetiger]

. I really need an electrical schematic but haven't gotten around to buying a WSM yet.

Attached is the electrical schematic for a BX25.

 

[yawning dog]

Awesome, thanks for the schematic! I went ahead and bought the WSM but haven't received it yet.

 

[yawning dog]

Hi whitetiger, the schematic was really helpful. I finally found out what was going on with the bizaare tractor wiring. The rear facing operator presence switch was entirely disconnected and two yellow wires were connected to each side of the front facing operator presence switch. So all indications were that the front seat switch was intended to work but it actually didn't. It turned out that while two wires were hooked to each switch terminal, they were the incoming and outgoing wires. So the switch was completely bypassed too. And there were 2 to 3 splices in each wire leading to each switch terminal that were totally corroded and making dubious if any contact. Long story short, I cleaned up all the wiring and just took it all off the switch. So now my seat switch is bypassed but I've already found that I needed to move the tractor a little when I wasn't in the seat so this is a desirable "modification" for me. Thanks again!