Sorry Folks......Another 8N 12v Conversion question

tinytanic1 · Jul 8, 2013

Thanks for viewing! 1948 8n, front mount distributor, new 12v coil(3.5ohms), new 12v battery, new alternator, new wiring harness. Reason....It had a 6v system, but old wiring was a rats nest with splices everywhere, so decided to replace with all new wiring and convert at same time. Starter circuit works great! Ignition circuit has no spark at plugs. With .3ohm original resistor, and 3.5ohm new resistor (both inline to coil), I am getting 5.5volts at wire at top of the coil, is this too weak? Wondering if this is too much resistance, maybe take the new resistor out? CAN ANYONE TELL ME WHAT THE VOLTAGE VALUE SHOULD BE GOING INTO MY 12V COIL without burning it up? My points and plugs are new and set correctly, and all my plug wires have continuity. I seem to be losing spark between top of coil (5.5v) and top of plug.

GManBart · Jul 8, 2013

You're confusing voltage with current....current is what cooks points.

What you need, is something under 4 amps to keep from cooking the points. Your 12V system puts out a max of about 14.6V. Use Ohm's law, divide voltage by current (in this case 4amps) and it gives you 3.65ohms. That means you need a total of at least 3.65ohms resistance to keep the current low enough to avoid damage, and a little more would be good.

Go measure the new coil, and see what the resistance is. I'd guess you're going to get about 3.5ohms. You added an additional 3.5ohm resistor, and that's cut the current down way too low.

You likely have 3.5ohms for the coil, 3.5ohms for the extra resistor, and .3ohms for the factory ballast resistor, for a total of 7.3ohms. 14.6v divided by 7.3ohms leaves you with 2amps, which is likely too low to work properly.

Take out the extra 3.5ohm resistor, and see what happens. R,

tinytanic1 · Jul 8, 2013

Your absolutely correct on these values, as stated in my thread, these are exactly the resistance values i have in my coil circuit. I just had no idea what my current or voltage values should be.. I will take out the new (3.5ohm) resistor when I get home today and let you know what happens. Thank you GMan !!!!!!!!!!

tinytanic1 · Jul 9, 2013

Got home last night, removed the new 3.5ohm resistor, tractor started right up. I wonder why they incl. it the conversion kit? Thanks GmanBart for the help! Two more problems tho. Tractor only stays running if choke is held out even at operating temp. Started with both carb. adj. at one full turn open, and tried playing with both from there to no avail. Idles and runs great as long as choke is out, dies if choke is pushed in. Also, the lift only raises at full throttle and bleeds down if not at full throttle or when trans. is in neutral. Is this normal???? Never had an 8N before.

tessiers · Jul 9, 2013

tinytanic1 said:
Got home last night, removed the new 3.5ohm resistor, tractor started right up. I wonder why they incl. it the conversion kit? Thanks GmanBart for the help! Two more problems tho. Tractor only stays running if choke is held out even at operating temp. Started with both carb. adj. at one full turn open, and tried playing with both from there to no avail. Idles and runs great as long as choke is out, dies if choke is pushed in. Also, the lift only raises at full throttle and bleeds down if not at full throttle or when trans. is in neutral. Is this normal???? Never had an 8N before.

resistor is if you run the original 6v coil, if you have a 12v coil you should not need it.

Sounds like you need a carb kit, simple and cheap. If you need the choke probably not getting enough gas somewhere along the line.

8n's had a weak hydraulic system, if the PTO is not running neither are the hydraulics. Sounds like you have a leaky lift cylinder, and possibly a weak pump.

GManBart · Jul 10, 2013

tinytanic1 said:
Got home last night, removed the new 3.5ohm resistor, tractor started right up. I wonder why they incl. it the conversion kit? Thanks GmanBart for the help! Two more problems tho. Tractor only stays running if choke is held out even at operating temp. Started with both carb. adj. at one full turn open, and tried playing with both from there to no avail. Idles and runs great as long as choke is out, dies if choke is pushed in. Also, the lift only raises at full throttle and bleeds down if not at full throttle or when trans. is in neutral. Is this normal???? Never had an 8N before.

Glad to hear it worked! As Tessiers stated, the 3.5ohm resistor is in case you keep the 6V coil, which has a lot less resistance than the 12V coil.

Sounds like a carb rebuild (worst case is a new carb at $110-150) is in order, and some seals for the hydraulic pump. Most 8Ns won't hold the implement up indefinitely without the engine running (the rate they leak down shows how good/bad the seals are), but it shouldn't take more than idle to lift the implement.