After I changed intake and exhaust valve guilds on a cylinder head, it doeson't start. It was running before the operation. The engine has compression and spark, and I cleaned a carburetor. I checked ignition timing is 3/8inch before top dead center. It has strong kick back and back fire but it doesn't start. Please tell me what can I think of why it doesn't start. Thank you!
Do you have manual or automatic advance/retard? I think the Super Rocket had manual advance as standard but who knows what might have been changed in 50+ years. You must have the advance/retard mechanism at full advance when timing it. If manual then the lever must be in the right position. If automatic then you must wedge the auto mechanism in the fully advanced position using small wooden wedges.\ HTH
Pushrods are in the correct place are they? If you’ve only done the head then the ignition and cam timing should not have changed... so why alter it?
If the pushrods are going the wrong way round then inlet valve will be open when exhaust is
Alternately, if you did change the timing... did you advance the magneto (assuming your still on manual advance being a Super rocket ( or wedge open the AAU mechanism if auto) when setting the timing to 3/8” btdc. From memory the crank angle is 37° or 38° BTDC for the super rocket. This will be more accurate way of timing.