1984 XT 600 ignition coil
 

My bike has been running, but it's very difficult to start, especially after it's warmed up. I'm trying to isolate issues, and my ignition coil seems to be bad. I'm reading way more resistance than spec. Does anyone have a good recommendation as to where I could find a replacement? The Yamaha part is running about $100 for the coil and plug boot, and that's a bit steep for my dirt-cheap budget bike, unless it's absolutely necessary.

I saw this on Ebay: Yamaha XT600 Ignition Coil 1984-1985 | eBay, but I'm a little suspicious, and it doesn't come with a spark plug boot. Any thoughts?

The high tension wire just gets screwed on/of so you can used the one from your old coil , otherwise buy any NGK plug boot and wire , look up the resistor value in the XT manual and get a cap in that general range .

Also check the spark plug boot resistance. They should be replaced regularly.

Okey thats new to me, please inform where you got this info from?

They have a resistor in the cap and sometimes this fails. I know this from personal experience trying to track down faults in old motorcycles over the years. Not sure if XT600's came from the factory with resistor caps but a PO could also have installed them. While I'm on it, best to replace the lead as well. the copper wires oxidize and corrode over time which also leads to poor spark. Make sure to use copper cable, not silicone. If it's difficult to find, try a marine store.

hope this helps!