retro

Yeah good reading, so the green/yellow is not shorted to ground which likely means that the ECM is bad. However, there is no way to test the ECM so the decision whether to replace it or not is all yours.

Me too! Glad ya had the cojones to make the call on the ECM 'cause I wasn't gonna.

Measurements look more trustworthy now. On your green to plug wire boot and black to plug wire boot, does your autoranging meter display 18.50K ohms? The range indication may appear in the corner of the screen where you may not notice it...... Also FYI just in case, the stack of metal plates sticking out of the end of the coil is ground for measurement purposes. With the 33p ECM connector unplugged and the green/yellow unplugged from the coil, check continuity or resistance again between the green/yellow coil harness wire terminal and ground. The result should be an open circuit.

I'm not saying your guides are bad... your 450 is low miles and if you've replaced valves before you won't need a machine shop. Likely just replace the valve seals and lap the valves in and run it.

@AKATV will be along shortly. Welcome to ATVHonda!

No point in riding it, just tear it down and fix it. Who knows, it might have been sunk... just gonna do more damage running it.

Well, epoxy melts at 450-550 degrees F, depending on the resin type so whenever those desperado days come around I'll be firing my WWII (mfg 1945) Tappan Deluxe!

I worked on a 450 once that had a loose valve guide (they're pressed into the aluminum head) that had risen up out of the head far enough that the underside of the valve spring retainer was hitting the top of the valve guide each time the intake valve opened, but the noise was intermittent and seemed to hammer more often when the motor was revved up. I fixed it by pulling the valve guide out of the head, cleaned up the guide and it's bore with 91% alcohol, then coated the guide and it's bore with Red Loctite and pushed the guide back in place. After cleaning up the excess Loctite I let it harden overnight then lapped that valve in to the seat with lapping compound and it's still running strong. You'll never know what you'll find wrong until ya open it up! Do you know how many hours/miles are on your 450?

I haven't opened one yet. I haven't even worked on any of the 420s or 500s that had a bad ECM yet. I'm just guessing but, those ECMs are probably potted in resin (like the old CDIs, Fan Control and Shift ECM modules are) which could mean they could be a bugger for desperados to repair.

Wow very nice machines! I envy you!

The experts have got your back! The only thing I can add is: do not EVER replace ANY part with a china knockoff. Buy genuine OEM Honda parts only, or else! I like Vince at Mr Crankshaft too, the Vesrah rods and his work are top notch.

I need a few days (very busy right now) to build a Peak Voltage Adapter for you. I'll PM you when I get one ready to ship.

We don't know enough about how the ECM controls the coil so we must assume that a good coil may possibly get hot over time without blowing a fuse. Just don't plug the next new coil in until we learn more about it. Order your next coil from RockyMountainATV beginning at this link to insure that you get a genuine Honda coil (part number 30510-HP5-601) : https://www.rockymountainatvmc.com/oem-parts/Honda

That sounds reasonable to me! DO NOT PLUG THE NEW COIL IN THOUGH! Just measure it when you get it and let us know those readings so we can analyze them. Mark the new coil that you have now and mark the new coil when it arrives so you won't get them mixed up while we test them. In the meantime I am going to try to build a Peak Voltage Adapter for you.

That's better, it looks like you have a secondary winding now. However, I don't know what the secondary should measure since the service manual doesn't publish that spec. But I expected to see the secondary measuring between 6.5k ohms to 9.8k ohms, within a similar range to the older model coils whose specs were published by Honda. So I don't know.... it looks wrong to me. Your primary winding measurement is higher than I expected as well, but it looks reasonable, so I can't shoot it down. My conclusion....? It's possible that your coil is bad but I can't prove my analysis without having a known good working coil in hand to test. I need to understand more about how the ECM loads and unloads the primary winding as well, with the only clue that I have to analyse those functions being that the Black/Red terminal receives battery voltage at all times while the ignition switch is on. I need a functional Rancher to test and learn from... so basically what I'm saying is that I'm not knowledgeable enough to help you decide whether the ECM (and/or coil) is bad or not.