1984 500 AE Wont Start

NEw top end, rebuilt ignition system by reputable Vintage Motoplat expert and still I can not get the bike to run. The longest it has run was about 30 seconds. Anyone have any suggestions?

I once broke a reed and could start the bike but it wouldn't do anything but idle or die. It probably wouldn't have run all that long without stalling if I gave it a chance. That is the closest to what you describe I have had happen. It was about 15 to 20 miles after getting it started from flooded by pulling with rope which I never did again and never broke a reed again. It was pretty much that cylinder and reed cage you have.

Pull the flywheel off to see if you have sheared off the woodriff key. You will still see spark and a wet plug, but it's not going to start because the fire and fuel are not dancing together.

Flywheel key is fine, gettting spark, but looks weak to me, but Im told these old Motoplats dont put out much. By chance I checked the compression.... only 65-75psi.... I think it's supposed to be 150psi. Now I am tjhinkingi need to have the head ground to get a good seat as I think this is where it is blowing by. Does any of this sound correct?

Try laping compound before doing any machining. Not sure what psi is supposed to be.

Are you sure your getting fuel? Did you try a few good squirts of starting fluid directly into the carb?
To get an accurate reading you will have to be giving a real good kick but 75psi seems to low, my 430s run about 130psi. Who put the top end together? Did you have it bored or honed? Did you check the ring end gap? Did you install the piston with the arrow pointing towards the exhaust port? Did you install the ring correctly on the piston with plenty of lube? Did the ring move freely on the piston?

You should be able to find more info in the Vintage Tech Ref and Parts section. If you can't find the exact shop manual, you should be able to find one for a air cooled 500 close to that year.