......I have a 1970 A65L... When I first take it out after sitting a day, it will start after a kick or two... and it runs great when it first starts. Comes off the stop light/sign strong and sounds awesome. I go a few miles on it though and it starts to get "tired" When I stop at a light or stop sign, I need to keep giving it some gas or it sounds like it will stall out...............Could someone share their opinion or offer me some guidance of what this might be? ....
This sounds like the idle may be way too rich. Does it idle nice when it is cold? .Lackluster mid range can be worn needle jets.
Easy starting combined with fading performance as it warms up and bad hot idle can be as simple as those two things. Idle usually speeds up when the engine is warm.
...... It will need a lil finesse to come off a light/stop sign by giving it more throttle than normal.... .... it will develop a knock for the first 10-20 yards when I'm first coming off a stop..........
But this knocking is more worrisome. A65 bottom ends are known to be a bit tender.
It could be pinging from low octane fuel, OR a loose con rod, or hopefully a loose primary chain.
I would first be making sure the ignition timing was not too advanced and that it had oil pressure. Run at least a 20-50 oil.
Keep in mind these bikes barely tolerate modern 91 octane fuel at 9 to 1 compression. Some of us run race gas to eliminate this problem and retarding the timing from the stock setting helps too.
Hopefully it isn't seizing up on you as mentioned by Quinten.
Best of luck with it. Let us know what you find.