Different PT 425 problem

[larrydman]

Been reading you guys problems with your 425's and was wondering if any of you has a line on mine. I've got 70 hours on mine and ever since I got it, it will choke out and die if I'm running anything other than the mower. With the mower it will run fine for hours on end, but with the bush hog or loader or anything else, it will run fine for a while and then choke out and die. After it sets a while it will restart and run a while longer. I'm no mechanic, but I've talked to a few and they are stumped (none of them have PT experience). I'm like Chris from PA, I love the machine when it runs, but I get aggravated at the stoppages. I can't trust the thing to do anything but mow grass. I don't know if it's something with the Robin engine or caused by hydraulics or what. I've cleaned and changed air and fuel filters religiusly but it makes no difference. Any help appreciated.

 

[Marks481]

Are you running it with Wide Open Throttle (WOT) with the mower, and with the engine idling otherwise? The air cooled engine isn't really designed to operate at idle speeds for extended periods of time (it will overheat).

Usually the choking and dieing problem is associated with vapor lock, when the gasoline boils in the fuel line or fuel pump (which is unfortunately mounted right next to the exhaust muffler). Several people have insulated their fuel line or relocated their fuel pump. Usually, however, this sort of failure is independant is more likely to occur after a long mowing session.

Maybe the blower fan on the top is helping keep your engine cooler while mowing (since the hydraulic temps get hot enough to trigger the fan), and your engien is overheating the rest of the time. Try jumpering out the temp switch (located on the cooler on the top inside of the motor cover) so the fan runs all teh time and see if you get different results.

Note this last isn't a permanent solution, since you would rather not purposely cool down your hydraulic temperatures as ambient temperatures drop below 60F, as it can make your tractor a bit sluggish.

Have you tried calling PT and talking to Terry, their mechanical genius?

 

[SnowRidge]

Welcome to TBN.

A couple of questions: By choke out, do you literally mean get too rich and die, or do you just mean sputter and stop from some unknown cause? A lot of folks have been having problems with their machines' vapor locking (the gas boils in the fuel line and the engine starves). You can search here and find a number of threads on the subject, with possible solutions.

If it was just the brush mower you were having problems with, I would wonder if you were just trying to cut too much material too fast, getting it too hot, and vapor locking. Since you are having the same problem with the loader, which doesn't use the PTO, I am stumped. Normally, running the loader doesn't stress the engine nearly as much as mowing, so I wouldn't expect you to get a vapor lock doing that kind of work if you don't get them when mowing.

Just to be sure, you do understand that the treadle is a kind of transmission control, not just a speed control like a car, and that when the engine bogs down because the load is too great, you let up on the treadle, not push down on it? A few folks new to PTs have not understood this point initially.

Lastly, are you operating the machine with the throttle wide open? You should. That is how they are designed to operate. The "throttle" is really an RPM control. The real throttle is controlled by the governor. Running with less than full throttle reduces engine cooling and lubrication.

 

[catsco]

Welcome to TBN.

Lastly, are you operating the machine with the throttle wide open? You should. That is how they are designed to operate. The "throttle" is really an RPM control. The real throttle is controlled by the governor. Running with less than full throttle reduces engine cooling and lubrication.

I'm concerned about several people saying that the machine is designed to be run w/the throttle wide open.

I did that for a short time, made a lot of noise, used a lot of fuel, and the engine compartment was VERY hot, boiling the fuel in the tank (steel tank in cover).

Since then, from 20 to 650 hours, I've used 1/2 or slightly more throttle at most, with no overheating issues, and am using a lot less fuel.

However, I am NOT mowing, which probably requires WOT, but am using the mini-hoe and front end loader for excavating, backfilling, and using the plow for snow plowing.

Mark H.

 

[SnowRidge]

I'm concerned about several people saying that the machine is designed to be run w/the throttle wide open.

I did that for a short time, made a lot of noise, used a lot of fuel, and the engine compartment was VERY hot, boiling the fuel in the tank (steel tank in cover).

Since then, from 20 to 650 hours, I've used 1/2 or slightly more throttle at most, with no overheating issues, and am using a lot less fuel.

However, I am NOT mowing, which probably requires WOT, but am using the mini-hoe and front end loader for excavating, backfilling, and using the plow for snow plowing.

Mark H.

That suggests that there is a design problem with your layout and/or muffler. It can't dissipate heat properly. By running the engine at less than full "throttle," you limit the amount of work it can do, since you are hard limiting the power that the engine can put out, but you are also limiting the engine's ability to cool itself. At a lower RPM, the fan will not move as much air, and the oil pump will not pump as much oil.

The best way to limit engine output is to back off of the treadle. The engine will do less work and use less fuel, but will still have full cooling available.

 

[Bob999]

If you are having a problem when using the loader I am wondering if the PTO circuit is "on". This could put excessive load on the engine. It would be consistent with your statement "I did that for a short time, made a lot of noise, used a lot of fuel, and the engine compartment was VERY hot, boiling the fuel in the tank (steel tank in cover)."

When you remove the mower and use the loader--do you turn off the PTO? When you turn the PTO off does it appear that the load is actually removed from the engine?

 

[J_J]

If you are having a problem when using the loader I am wondering if the PTO circuit is "on". This could put excessive load on the engine. It would be consistent with your statement "I did that for a short time, made a lot of noise, used a lot of fuel, and the engine compartment was VERY hot, boiling the fuel in the tank (steel tank in cover)."

When you remove the mower and use the loader--do you turn off the PTO? When you turn the PTO off does it appear that the load is actually removed from the engine?

Bob,

If engine is running, I don't think he could disconnect the hydraulic lines if the PTO switch was on. If the PTO switch switch is on when starting, will it even start or start and kill the engine since you are only pushing fluid against the relief valve. If the PTO switch is off, there is no pressure, PTO pump is just pumping fluid back to tank.

 

[Bob999]

Bob,

If engine is running, I don't think he could disconnect the hydraulic lines if the PTO switch was on. If the PTO switch switch is on when starting, will it even start or start and kill the engine since you are only pushing fluid against the relief valve. If the PTO switch is off, there is no pressure, PTO pump is just pumping fluid back to tank.

JJ, I generally agree with your observations. I don't ever connect or disconnect the PTO lines with the engine running and I guess I just assumed that everyone does it that way. Maybe I should have said that perhaps the PTO valve is sticking in a partly open position--just enought to put excess load on the engine but not enough to prevent engine starting.

 

[larrydman]

Hey Guys,
Thanks for all the input. The vapor lock theory seems reasonable. I do run the loader and tree shear at reduced RPM and maybe the bush hog but I think I run the boom mower at high RPM and it has happened with it, but it's possible I didn't have it that fast when it happened. I'll try it out when the weather breaks and see if it makes a difference. Like I said, I'm no mechanic and can't tell whether it's a flooding or starvation problem.

 

[SnowRidge]

Also, you may have a little bit of more than one problem, which all come together under the right circumstances.

One of them may be a clogged fuel line. The angled hose barbs under the tanks have a habit of clogging with trash, especially on new machines. Check your clear fuel filter. It will have what appears to be an air pocket in it. It's actually fuel vapor, and is normal. If it grows as you operate until there is no fuel in the filter, it is an indication that your angled hose barb may be partially clogged.

Run a wire up into that fitting, if you think it is clogged. Needless to say, don't do it with a hot engine or any ignition source around, as you will inevitably spill some gas in the process.