switch key purpose late model A

[Mark Pengelly]

Can anyone help clarify how my key switch on my late styled 1950 A is supposed to work please?

I think I have a mag system:
a WICO model X, type XH-1042
and a generator with number 99 70 GD 1755
on it.
It"s setup up with positive ground 12v

To kill this tractor I have to ground the post on the side of the WICO unit right? (I know I can do the petrol turn off thing also and that that"s recommended by some).

The thing that puzzles me is that when I got the tractor (I think) the kill post from the WICO was wired through the key switch on the dash to ground. That means that to switch the tractor "off", I have to turn the key "on", ie circuit to ground is completed then, (and vice versa).

I"m struggling to believe that this is how things are supposed to be? It means for one thing that when the key is removed the tractor is startable (circuit open and mag sparking). So whats the point of a "key" switch in that case?!

Haven"t figured out an alternative way of wiring that switch so it"s the other way round. Is there one?

Perhaps my tractor has had the magneto retro fitted and the key switch belongs to a previous distributor/coil setup? I always thought that a late styled A like mine might not have a mag.

Thanks for help or comments

 

[Anonymous-0]

You are right your tractor came with a delco dist

 

[John T]

If the key switch (assuming its a simple On/Off SPST) was made for a Distributor its NOT the same as if for a Mag but sounds like you already figured that out...... A Mag switch (could be an On/Off Push/Pull switch) does as you suspect when ON it ungrounds/open but when OFF it (closes) provides a ground via a wire from it down to the kill terminal on the Mag. One sees all sorts of farmer modifications on those over the years as the switches often go bad and arent replaced with a correct unit ESPECIALLY if the tractor gets switched to or from a Mag versus a distributor. I HAVE NO WAY TELLING WHAT YOU HAVE THERE if its a SPST or SPDT or what, if it were a 3 terminal SPDT one could rig it up but its probably just a 2 terminal SPST which can still work if you wire it to ground the mag butttttttt it may then be in the ON positiion grrrrrrrrrrr

Jim up at Agri Services in New York www.wiringharnesses.com can probably fix you up

If theres kids around I prefer a key switch although an On/Off push pull is easy and handy, you already understand what it has to do with that mag so its a quick n easy job.

I STILL LIKE TO TURN THE GAS OFF N LET THEM STARVE but thats not so critical in an elec start tractor versus a hand cranker but still a good safety measure in case the carbs needle n seat or float dont work. You can still use the switch n then turn the gas valve off of course.

Nuff said

John T

 

[d. coleman]

check to see if you have a terminal on ign. switch that is "grounded" with ign. switch in off position and "open" with key in on position. if you do run a wire from that terminal to wico mag terminal or get a "momentary contact" push button switch from Radio Shack or auto parts store. this will ground mag. out only when pushed in and held. one treminal to tractor body the other to mag. terminal. good luck, d. coleman (48M&51B w/wico mag.)

 

[1944bgardner]

My B had a toggle switch to magneto, I could never remember which position was to run. Makes for alot of unnecessary hand cranking. I just used a feeler gauge at the magneto post.

 

[almrm]

John,

I agree that starving them dead is the best and storing them with the gas off is best.

The operators manual for a late A with a gasoline engine and magneto ignition states that to stop the engine simply pull the throttle all the way back.

My A would always stop like that for the 40 years that I can remember and the 20 years before that according to my father, who bought it new.

I gave it the Roberts Carb drill bit treatment and cleared all 5 idle passages in a 2005 rebuild and now it does not stop at zero throttle. It just drops to a perfect very slow idle. Actually, I kind of like it better this way.

My Point - Clearly the carb is designed to run the engine with the throttle closed. Why did the engine stop at zero throttle when the tractors were new? Did it had a little cap plug or restricter somewhere in the idle circuit? Just curious.


Mark

 

[John T]

Good question BUT I CANT ANSWER IT..... On many I owned the vertical spring would serve as a throttle stop which could, if forced, naturally bend/spring enough so the throttle plate would close so tight it would kill the engine....but an otherwise pull the throttle all the way back still allowed for a good slow idle.

When rebuilding a carb I recall for a good slowwwwwwwwww idle its critical the throttle plate be perfectly concentric to fit the bore evenly but JUST DO NOT KNOW about any bleed circuit or by pass whereby if the plate is full closed she would still run????????

Hopefully a carb expert will enlighten all of us.

John T

 

[alabamafrog]

Below is a pic from my SM2024 carb manual, it shows that there is an idle circuit that comes into play when the throttle plates are fully closed.

Apparently if everything is set right then she will continue to run on the fuel and air that comes through this orifice.
Both of my A’s are All Fuel magnetos and the mags do not have a grounding screw so I have no choice but to either turn of the fuel selector valve and wait for her to starve or in an emergency I can pull the throttle back and choke her down, but I wouldn’t recommend that because it can cause too much fuel to be in the cylinders after she dies.
I just went back and read through my operator’s manual and was surprised to see that apparently the gas tractor is supposed to stop by pulling back the throttle and nothing else. I always shut off the fuel and starve them then also turn of the mini ball valve I added at the carb for double insurance. I do this even on my 60 that has an ignition switch, my problem is remembering to turn the ignition switch off after it dies so the coil don’t fry.
I think the gas burners and all fuel models had different carbs, I wonder if there was something different in the idle circuit to explain this?

 

[Roy Crane]

If you go to an aircraft supply site, such as Aircrft Spruce Inc, they will have ignition switches for magnetos. They stay grounded in the off position.

 

[Mike Aylward]

John, that spring is not used to allow the engine to die. That small spring on the carburetor is to take out slack so the carburetor butterfly won't "hunt" at a slow idle due to the intake pulses of the engine. The peg is what controls how closed the butterfly goes. If the peg is straight (many are bent so the tractor WON'T die) the tractor will die IF the throttle shaft and butterfly are in good condition and the stop screw is adjusted properly. If any of these conditions are not met the tractor will not die. We always bent the peg a little bit so when the throttle was pulled back the tractor wouldn't die. Not a good thing at the end of the field. But they can be set to kill the engine without too much trouble. Mike

 

[John T]

Thanks Mike, I was hoping to get an answer on that. I sure hate to miss GOG I just called Tony yesterday n told him to take me off the Seminar list for next year at least, maybe in 2012? We are in Florida then and its just sooooooooooo long to drive n then go back South. Its always been fun to catch up with you n others at that great show.

John T

 

[Mark Pengelly]

THANKS everyone for your comments and replies.

I think it"s John T"s and Kent P"s replies that are really getting to the heart of my question.

Perhaps I should have said that I"ve just about finished restoring this tractor (just lights and decals to do) and I"m trying to be as original as possible.

With regard to what type of switch I"ve got John, it"s simple 2 terminal SPST, it looks so good on the dash that I"m fairly sure it"s a genuine part of the original tractor. It"s looks just like the ignition switch found on pg 26 & 27 of my parts manual, part No. AB4087R

So Kent, how are you so sure I should have the Delco distributor? My tractor serial No is 649004. According to my parts book the Delco Coil/Dizzy rig seems to belong to tractors 662874 and above. On the other hand the Wico Distributor/Ignition Lock setup (is that a kind of distributor with built in coil??) belongs on machines 659290-662873.

They"re the only two setups I can see that use the AB4087R key switch, but they don"t seem to go with my serial No.

So that makes me feel the Wico X Mag might be right on the machine after all, perhaps the key switch is the red herring?

 

[Mike Aylward]

We'll sure miss you there, John. The new place sounds like it will be really nice. We are already making plans to go and are looking forward to it. I know warm weather would be hard to beat at that time of year. Mike