Spent many many hours on one of those.... we were lucky ours had electric start. Best tractor to cultivate, front mount of course, will run a silo blower all day on 5 gallons of fuel and will pull a 4 bottom plow. Until the 4020 came along this had to be one of the best JD ever built.
I can remember running a 720 and an ol R when I was a kid they were easy on fuel and worked hard that was Bach in the 70's they were ol back then good to see you guy fixing one.
My Grandfather had a 720, 520, B, an A and horses before that. We have them restored now (the tractors not the horses) and looking like new. I spent many hours on them growing up. The 720 was a good workhorse for sure. The B was kid friendly and the first tractor I learned on. Spent time wrenching on all of them, back when you could get parts. But at least they don't require computer chips and you can't get squeezed that way. LOL
Cool! Haven't heard one of these in a while. We used to have a 730 . The pups are indeed expensive to work on, we had to rebuild ours once and I don't even think it lasted a whole summer before it cratered again... That was like 40 some years ago though and our mechanical skills were a little sketchy, lol!
We are keeping the pony for old time sake I'd like to find another and make it electric start for a chore tractor it sure is nice to jump on the 620 hit the pedal and go!
What we've done to break gas motors loose is mix atf with diesel I think, but that was on my great grandpa's 1939 A, it had sit for I'd say 40 years in the one Quonset and then before that in a old shed, which that A after sitting so long was still free, you could spin the flywheel pretty good
When they are well worn, they can be quite a challenge. When they were 10 years old, you could turn the steering wheel with one finger if it had a 2 row picker on it or a loader bucket full of manure.