4020 does not shut off

[brians in sd]

I have a 1970 JD 4020 diesel that will not shut off especially in summer or when the engine is warmed up for a while. But it also would not start either sometimes until you "bumped the switch" several times, so I replaced the ignition switch thinking that it could be causing both problems. Well, it solved the starting, and it starts fine, but sometimes in the worst case situation I have to kill it in road gear and pop the clutch. But in most cases if you turn it to off position, it will run maybe less than a minute and shut off. I have checked the lead going to the Roosa Master pump with a test light, and with the tractor NOT running keyed the switch back and forth and it tests out like it is supposed to. Any thoughts what I need to check out next?
 

[gregger]

sounds like u neeed to buy a book -- 4020s dont shut off with a switch ' the throtle shuts um down -- pull the nobb and left up , same with starting pull down
 

[9630]

THE later models shut off with the key the early models shut off with throttle lever check the electric wire going to the pump i had that trouble on my 2520 i just cleaned the connector as it has some oily residual in it worked fine after that.
 

[DONMYEIL]

Replace the o-ring on the shut-off solenoid plunger in the pump. Should fix it .
 

[MisterT]

[MikeinKy]

69 and newer shut off with the switch.
 

[LJD]

Which pump? Stanadyne Roosamaster C pump or the DB pump? Big difference.

C pump has a wire that plugs to the side of the pump with a push-pull connector. These are known to stick and not work. Little metal plunger in a cylinder bore with a spring. The spring pushed it into "off." Electromagnet pulls it into "on." Little o-ring at the end. If it sticks - or - if the o-ring is bad it won't shut off.

DB pump has a wire that fastens to a stud with a nut on it. Solenoid is inside and has no direct mechanical connection to shut the pump "off." A spring turns the pump "off" and a weaker spring turns it "on." Solenoid electromagnet assists the "on" spring so it can overtake the "off" spring. Again - the solenoid had a plunger inside a cylinder and can get debris and get stuck.
 

[wilamayb]

Don't you just hate when you have to remove your foot from your mouth? :)

Btw... It's knob not nobb.
 

[johndeerefan]

My 69 4000 diesel had the same problem. I replaced the shut off solenoid switch on the side of the Roosamaster pump (hard to find part!). Problem solved.
 

[brians in sd]

Thanks for all your suggestions. I think several of you have nailed it with the o-ring/plunger on the pump. That sounds very much like the trouble. Thanks again.