Ford 640 - How should the coil be wired

I was recently gifted a Ford 640 tractor. Pulled it off the trailer and the battery was dead. I purchased a new 6v battery and connected it to the tractor, positive going to the right side (passenger) and negative to the left (driver). The tractor cranked right up and was driveable but obviously wasn't reaching it's full potential as backfiring occurred at higher RPM's. I pulled the tractor into the barn and backed off the throttle to Idle whereupon it died. The weather turned colder and I wanted to go plow the driveway but could not get the 640 started no matter what I tried, plenty of fuel was flowing through both the filter and the carb (checked the drain plug on the carb).

I assumed it was a coil or spark issue so I purchased a new coil from Tractor supply. I wired the coil with the positive going towards the rear of the tractor (ground?) and the negative going to the distributor. This seems correct to me in a positive ground situation as the negative is the hot lead. When hooking up the coil the darn ground (rear) wire broke apart due to age so I stripped the end of the lead off for testing, I was able to get short bursts of spark but tapping the positive lead on the coil with the stripped wire and the tractor fired! My issue is that now I get no spark when touching the coil and the tractor refuses to start again. I have no idea if the coil is wired properly because every post I read says something different in regards to positive or negative ground situations.

Any help on this would be greatly appreciated.

Thanks

Here is John in la"s 6V Positive Ground wiring diagram for your 640.
6V wiring

Sounds like you not good with basic wiring in general. Saying left and right means little or nothing to us since we can not see the tractor. That said it should be a + ground tractor meaning the + battery cable should be bolted to the frame some place and the - to the solenoid. The coil should have the + side of it going to the distributor since the points are what ground the coil and the - to the ignition switch. Next pull the distributor cap and rotor and dust cover. Get the points closed and carefully open and close the points by hand. You should with the ignition on both see and hear spark and if you do not then clean the points or replace them good chance the points are dirty or corroded. By the way if you not careful you may find the spark the hard way by ground the point by way of your body

Should the coil still be okay if it started with the negative connected to the distributor?

Sure should, as a matter of fact it works just fine either way!

ditto what jmor said.

the coil backwards thing is something you could see on an oscope or other specialized equipment.. etc..

Thanks guys I appreciate all the good info. I'm going to check the points this weekend.

It's running like garbage currently but I attribute that to it being a south Texas tractor that was transplanted to northern Kansas in sub zero temps.

Yes coils are pretty much bullet proof and the only reason it should be hooked up the right way is so the spark jumps the correct way

some tractors need a lil more main needle in the cold. you can test this with a tug of choke...

Also check the air cleaner. Those are one thing few people service and can cause many problems if filled with water which if cold will freeze and then you get a non-running engine

(quoted from post at 19:01:33 03/28/13) Also check the air cleaner. Those are one thing few people service and can cause many problems if filled with water which if cold will freeze and then you get a non-running engine

Click to expand...

Once again I appreciate the info.

I have the tractor running at idle but it seems to be missing. When I advance the throttle to high RPM it runs decent for a bit but when warm I can't bring the throttle back down or it will rev from high to low and eventually die.

On a possibly related note, quite a bit of fuel (a puddle) is leaking from the carb when the tractor is off from what appears to be the throttle linkage. I'm assuming it needs a carb rebuild but I didn't know if the missing and inability to go to low rpm is mostly spark related.

Thanks

(quoted from post at 22:16:13 03/28/13)

(quoted from post at 19:01:33 03/28/13) Also check the air cleaner. Those are one thing few people service and can cause many problems if filled with water which if cold will freeze and then you get a non-running engine

Click to expand...

Once again I appreciate the info.

I have the tractor running at idle but it seems to be missing. When I advance the throttle to high RPM it runs decent for a bit but when warm I can't bring the throttle back down or it will rev from high to low and eventually die.

On a possibly related note, quite a bit of fuel (a puddle) is leaking from the carb when the tractor is off from what appears to be the throttle linkage. I'm assuming it needs a carb rebuild but I didn't know if the missing and inability to go to low rpm is mostly spark related.

Thanks

Click to expand...

Its always a good idea to shut the fuel off when the tractor is off.
The fact that its leaking is, as you said, is an indication of it needing carb work.
At the least the needle valve is not seating correctly.
That's a pretty common thing on tractors that have set for a while though.
A decent carb rebuild may solve the majority of the problems.
Still a good idea to service the air filter and any other items that have been neglected.

As Royce said good to shut the gas off when not running or you can get gas in the oil and that can mean an engine rebuild. If in fact the leak is at the throttle shaft that is a vacuum leak and that will cause odd problems and needs fixed

When the points open we have an alternating voltage so polarity doesnt matter.