Hi, I just joined your fine site due to taking ownership of a 73 RT360 Enduro. My brother gave it to me after sitting in his garage since 97. The oil had completely leaked out so it wouldn't go into gear and kick start was locked solid. I opened up the clutch cover and the clutch was dry and crusted so I hit it with a lot of PB and got it all apart and managed to get it all apart. Cleaned up all the plates and soaked them in oil and reassembled, clutch works now - it will need a new clutch if I get it going. Buttoned it up and filled it with oil. I also removed the plug and sprayed in some seafoam last night. So far still locked up, not sure if oil in the crankcase will do any good to loosen things up. I would appreciate any advice on next steps. He said the bike ran before putting it away so I don't think it seized before it sat. Thanks! -G

Congratulations on the cool bike
if it’s locked up with clutch pulled in then you might want to take the head and the magneto side cover off and see what’s going on, could have rusted up? 

The bike is currently stuck in neutral and will not go down into 1st or up into 2nd. Kick start shaft rotates slightly then comes to a dead stop. I suppose the  piston is rusted tight, I gave it another heavy shot of seafoam tonight and see what tomorrow brings

Regarding stuck in neutral, the detent plunger on the left underneath might be rusted up considering what's possibly been going on over its time in hibernation--no oil etc.
The piston has likely grown into the cylinder with alloy corrosion. Or the rings have rusted to the bore. Might get lucky by forcing the flywheel back & forth if it'll try & move. Best of luck & been there done that many times & got them going in the end. Great satisfaction 'that'.

 from Salisbury, UK.

Look up the VIN of your bike and then use the VIN tables in the Tech Library (see top toolbar) to id exactly which model you have - sounds like a RT3.

Once you're happy that you can get the bike running and mobile, change out front and rear brake shoes - they are still available from Yamaha.

If you plan on using the lights, then fit a voltage regulator - see link below.

Vintage Yamaha Enduro Fans - Service Bulletin #M5-084 re Voltage Regulators (yamaha-enduros.com)

You will need to apply some force to the flywheel using something like my holding tool. If you make one just don't make the pins too deep & catch the coils. I'm sure you'd be onto it but just saying. 

Welcome from the Space Coast of Florida.

Greetings from Tennessee  

Thanks for all the responses! I took off the Magneto cover and put a ratchet on the bolt - the piston broke loose and is now moving up and down nicely with no scraping noises! Kick start operates now. I have the plug out and plugged into the cable with the plug touching the head - no spark when kicking it. Do I need a battery to get spark? What should I check to get spark otherwise? Shifter is still stuck in neutral 

I'm sure there's going to be smarter peeps than me come along soon but I'd clean the points before doing anything, sitting that long I'm sure they are pretty corroded and no you don't need a battery to start it but I'd disconnect the lights or you will blow them, the battery acts as a buffer (I'm sure that's not the right terminology), to soak up the extra power the mag makes.