Did you back off the all the adjusters until they just about fell off, before cover install? And hold them up off the valve stems with rubber bands or something?
Bent valves can take out the guide, but it's not guaranteed. A bent valve should at least be tight in the guide, I would think.
There is a way to find out without taking the head off and wasting a head gasket.
1st do a compression check, and then check with a couple drops of oil. Oil will seal leaky rings temporarily but won't seal a bent valve.
Probably a better check for this is a leak down test. You bring the piston to TDC hold it there and put air pressure in the chamber. If you can hear it leaking out the intake into the carbs, then you know there is a valve seat seal issue.
Another way, after removing the cylinder cover, is to use curtain draw cord. Move the piston down in the #2 bore about 1/2 to 3/4 inch. Then feed in about 10 inches of the curtain draw cord. Next bring the piston back up to mash the cord between piston and valves. Don't force it, we are just trying to hold the valves up in the seated position. Lock the crank in this position. You can now remove the valve spring from the suspect valve, and check for side play in the stem. Move the crank a few degrees if necessary to push the valve down no more than 1/8 inch. The valve should not be sticking and move freely this amount. If tight and difficult to move with bare fingers, you got a bent valve.
If some or all of the above tests indicate a bent valve or leaking intake valve, you will have to at least replace the valve. And, if the new valve does not work in the guide properly or the guide is cracked, then the guide must be replaced, too.
After you have verified that the engine mechanicals are where they should be, then you should revisit the carb sync. and spark timing.
Hope this helps,
