Motorcycle Repair: 1978 CB400 Hawk valve stem seals, nylon rope, rubber glue

Question
I just bought this 1978 CB400 Hawk. It did not run because the carbs were full of varnish.
I took them apart and cleaned everything but the "AIR CUT OFF VALVES" I thought they were fuel pumps.
It ran great.
Then I thought I should have cleaned those valves.
I took off the cover of one carb (while still on the bike) It was all gummed up also, I think I damaged the diaphragm while trying to remove it, cracking the rubber fabric.
I put it back on, and it ran extremely WHITE lean on that side and would not fire with higher RPM. I ordered new "air cut off valves" they should be here this week. I also noticed some smoke at start up.
I would guess it is valve stem seals.
Are the valve stem seals just under the Head cover (valve cover)?
I really don't want to get into anything more then that on this bike, (like head removal)

Answer
It sounds like the diaphragm got damaged or is not sealing properly. I'm afraid you will need to replace it. You might be able to repair it will some rubber glue but I've never heard of anyone getting to work right that way.

The smoke on startup is likely due to the valve stem seals.

See item #2 in this diagram:

http://www.bikebandit.com/houseofmotorcycles/showschematic/m9439sch406476

Replacing the seals is not a simple task. It involves removing the cam and followers and compressing the spring (held on with a split cotter #19).

It's possible to do this without removing the head by carefully positioning the piston, feeding some nylon rope (via the spark plug hole) into the cylinder and compressing the rope into the combustion chamber. The rope will keep the valves from dropping into the chamber. When you are done, you uncompress the rope by dropping the piston and remove the rope.

You will still need a tool to compress the valve springs, though. Normally this is done via a large C-clamp but with the head off. If you leave the head on you may need to make a tool. Possible something that will bolt onto the head via the camshaft guide bolt holes. Motorcycle mechanics usually have a large collection of specialized tools for these jobs.

With the valve cover off it will look like this:

http://www.bikebandit.com/houseofmotorcycles/showschematic/m9439sch404216

The eight holes are visible once the camshaft is removed. These are threaded.