engaging the pto kills the engine

[JCD 80]

This might be a tough read as I don't know what the parts are called and didn't have my camera with me, I hope someone can follow along and give me some assistance.

 

There is a rod that goes from the carb to the right when looking from the seat, when I push the part the rod is connected to the engine revs higher,  when I let it go it returns to idle,  

 

I had the hood up and engaged the pto and I watched the rod move all the way to the right and kills the engine.

 

I know this is the problem what I don't know is why would engaging the pto cause this to happen and what should I do to fix it?

 

I tried pushing it back and the last time I tried the pto the rod didn't move and my engine stayed running with the pto fully engaged.

 

Thanks,  Jim

[squonk 43,811]

If the seat switch is still working the PTO will kill the engine unless you are sitting in the seat. 

[953 nut 59,984]

The small rod you are talking about is connected to the governor. When engine RPMs go down the governor will move to open the throttle further. This is not what is making the engine stop running. As @squonk said the seat switch has to detect weight (you) in the seat when the PTO is engaged or the ignition will be cut off, this is a normal function of the safety switching. 

[JCD 80]

I thought the seat switch had been removed, there is no button, it's flush with the bracket under the seat and I don't see anything under the seat to depress it.

 

If it were the pto safety switch why did my engine die when I was mowing or sitting still but in the seat?

 

I did notice when the governor rod moves to the right that is when the engine dies,  when it stays in place to the left side the pto can be fully engaged and the engine doesn't die and I can cut the grass.

 

I'm not discounting what you guys are saying I'm just trying to make sense of what I'm experiencing.

 

Thanks,  Jim

[953 nut 59,984]

2 minutes ago, JCD said:

there is no button,

Flip the se3at up and see if there is a pair of wires running to the seat. Many newer garden tractors have a seat switch built into the seat.

[JCD 80]

I'll take a look when I get back up to VA

 

Thanks,  Jim

[Handy Don 14,062]

The goal of the seat+PTO interlock is to lessen the damage when doing things like standing next to a running tractor not realizing your toes are under the mower deck and deciding to engage the PTO. 

[gwest_ca-(File Mod) 11,482]

The throttle cable is connected to a spring that is connected to the governor linkage. When you go to high rpm with the throttle you are increasing the tension on the spring and the governor linkage responds.

The governor is driven by the engine camshaft and the faster it turns the more pressure it applies to the same governor linkage trying to slow the rpm down.

When the spring pressure on the governor linkage equals the pressure developed by the governor on the linage is equal that is the resulting rpm.

If the throttle position does not change but the engine slows down the governor pressure is reduced allowing the throttle linkage to increase the speed. 

If the throttle position does not change but the engine speeds up the governor pressure increases reducing the spring tension on the cable so the engine slows down.

If the engine quits or slows down with no change in throttle position the governor pressure is reduced allowing the spring to take the carb to wide open throttle.

 

Post your model number and serial number so we can look at how your seat switch was wired. That will explain why and how the pto kills the ignition. 

[JCD 80]

312-8  year 1990

3112k 801

11289

 

Thanks,  Jim

[kpinnc 14,641]

I would just pop the pins and remove the PTO bell and see if engaging the lever still affects the engine. 

 

If it doesn't, the bell had a stuck bearing (assuming you have no deck on the machine) or your deck has a stuck bearing. This would also cause the governor to respond before choking down.

 

If the engine does still shut off with no PTO in place, you have an interlock issue. 

Edited July 25 by kpinnc

[gwest_ca-(File Mod) 11,482]

You have magneto ignition so the seat switch grounds the ignition wire with no operator present which shuts the engine off. This is done through half of the pto switch.

Magneto ignitions are self-powered and grounding the ignition wire shuts it off. Never allow any battery power into the ignition wire as that will burn up the coil.

If you can find the seat switch wire connector make sure it can not get in a position where the orange wire can not be grounded.

The black wire in the connector is chassis ground and the green wire goes to the row of indicator lights.

 

[JCD 80]

I checked the bell with the belt off and had no problems I engaged the pto several times and it never shut off but I didn't try it without the bell.

 

I cleaned then checked the spindles, pulleys, idlers on the mule and no sticking or difficulties everything moves smoothly on the deck now.

 

The only thing I notice is sometimes when I engage the pto the governor moves to the right fully and the engine doesn't rev up at all it just sputters and dies unless I pull the pto lever back then it comes back to life even if the belt is just still barely moving.

 

I thought if it were a safety switch it would just cut out and I'd have to restart but if the belt is moving even barely it will roar back to life if I disengage the pto.

 

Jim

[953 nut 59,984]

Sounds like the mechanical portion (PTO, Mule Drive and mower deck) are not the problem. Also, electrical and safety switches seem to be working fine which brings us down to the engine's ability to respond to a load. Could be the carburetor needs a good cleaning and air filter or something is restricting the exhaust.

[Gasaholic 294]

Governor rod thing is a red herring. It is a symptom so to speak, not a cause - Engine is shutting down or not getting enough fuel, if you have it at full throttle, it is gonna move to the right (it'll do that too if you turn off engine with key switch while watching it)  So ignore that.  Your problem is either the Seat switch (safety switch system) or the engine is cutting out or starving for fuel. Since it is intermittent and cannot be duplicated 100% of the time, it is probably NOT a fuel issue.  Most likely your seat switch is intermittent. When you sit in the seat, the actuator is opening the switch so that when PTO is engaged (PTO switch for ground path closing) the ground path travels through the seat switch , which if that is open properly, engine will stay running. If the seat switch intermittently is not opening, it will ground the engine's magneto and shut off the engine (which results in your observed governor rod movement)  What you need to do is verify your switches work 100% . In the PAST it was possible to just unhook the wires from the seat switch which disables that safety feature (Making it dangerous to operate in that condition. Even I, with over 40 years experience professionally repairing and operating do not like to operate a mower without that seat switch working properly!)   

 

HOWEVER you also point out that operation with the mower drive belt disconnected seems to operate properly?  In that case, I'd be thinking that you may have a wiring or connector issue (something's touching ground when you engage PTO and it is loaded) so I'd carefully examine wiring harness to see if it is rubbing anywhere all along where the PTO rod, linkage and lever are operating.  Either that, or something is shifting when you get out of the seat to unhook drive belt from mower - If you can "prove" it works with belt disconnected, try again and get up out of the seat while you have PTO engaged and mower belt is off - engine should start to die, and then recover when you sit back down in the seat. If you can get that to happen 100% of the time, your seat switch should be working properly. However, chances are if your switch is intermittent, you can trigger the shut down by standing up out of the seat and then sit back down and the engine still dies, then your seat switch is bad. 

 

Beyond that, if everything else proves out, then your engine cannot handle the load (Generally that'd mean carburetion's high speed circuit, or possibly a valve, weak compression or intermittent spark problem) 

Edited July 25 by Gasaholic