IH 454 electrical question

Hi everyone. I bought an IH 454 4 cyl gas about 2 years ago and here's some background on issues I've had with it. If you want to just read my question, feel free to skip to the bottom haha.

When the tractor is cold it will run fine until it gets up to normal running temperature and then it slowly starts to miss gradually getting worse until it won't run at all. I fought this for almost 2 years trying to insulate fuel lines to prevent vaporization, test the intake manifold, had the carb off cleaned and adjusted dozens of times, lead substitute to help prevent sticky valves, other fuel treatments, cleaned and adjusted points several times...

I realized back in the spring (by dumb luck) that if I clip a jumper wire from the positive terminal of the battery directly to the coil terminal, the symptoms are drastically reduced and while the tractor will still miss and not run perfect when hot, its still mostly usable. I went to use it over the weekend and the battery was dead so I jumped it and used it for 10 minutes until it shut off due to a fuel issue which ended up being a chunk of permatex that clogged the fuel line at the filter bowl and stopped the fuel.

With all that said, when I tried to restart the tractor after it shut off, the starter solenoid wouldn't even click and after some cleaning of the clutch permissive switch and checking connections I realized the battery is no good. It reads ~10V as it sets in the tractor right now.

My question is, with the ignition switch off, I get ~10V across the battery. When I turn the ignition on, it drops to ~8V. Is a 2V drop reasonable? Or is that too much? Its a 12V coil on the tractor (not a 12V start 6V run kind of deal) and I'm starting to wonder if I don't have a bad wire/connection that when the ambient temp of the engine compartment gets hot, that there's a big resistance somewhere which is drastically dropping my voltage to the coil and causing the tractor to run poorly. Since a jumper wire directly to the coil makes it run better, that makes sense in my head but I'm looking for some guidance of where I can start troubleshooting for a bad connection causing that kind of voltage drop. Would a shop manual have a wiring schematic for this tractor? I apologize for the lengthy post. Just wanted to make sure all the information was there.

Thanks

Battery should be at 12.6 Volts and drop VERY little when key is switched on, it's obviously DEAD.

The ignition circuit only draws 3 or 4 Amps, and so it doesn't take a very large gauge wire to get power to the coil without much of a voltage drop.

I've attached a link to the wiring diagram so you can follow the ignition wiring and find your voltage drop.

Also, if the coil is "weak", even a small voltage drop will weaken an already weak spark enough to cause misfire.

Also, check the coil-distributor cap wire for continuity. If higher resistance than normal, it will weaken spark. I'm assuming it's a carbon-core suppression wire, typically 7000 Ohms per foot resistance, give or take a bit.

Check out the cap and rotor, as well, make sure the carbon is not missing where the center of the rotor touches the cap.
Wiring diagram

(quoted from post at 07:05:32 07/10/18) Battery should be at 12.6 Volts and drop VERY little when key is switched on, it's obviously DEAD.

The ignition circuit only draws 3 or 4 Amps, and so it doesn't take a very large gauge wire to get power to the coil without much of a voltage drop.

I've attached a link to the wiring diagram so you can follow the ignition wiring and find your voltage drop.

Also, if the coil is "weak", even a small voltage drop will weaken an already weak spark enough to cause misfire.

Also, check the coil-distributor cap wire for continuity. If higher resistance than normal, it will weaken spark. I'm assuming it's a carbon-core suppression wire, typically 7000 Ohms per foot resistance, give or take a bit.

Check out the cap and rotor, as well, make sure the carbon is not missing where the center of the rotor touches the cap.
Wiring diagram

Click to expand...

Thanks Bob. I'm buying a battery now. I'll check on the other items when I get home.