Do my valves need adjusting and if so how?

[Coca Kohler]

I have a 1985 MTD with a 14hp opposed twin Briggs and Stratton. Engine codes are model 400707 type 0114 code 85082312

 

[Coca Kohler]

There is a ticking/clicking sound which is coming from the engine which I think is the valves. It appears to run ok except the choke has to be mostly out and has to be adjusted depending on how much throttle is used and sometimes it makes a popping sound. Also as its not a OHV I don't know how I would go about adjusting them and what should the gaps be in mm's. Any help would be much appreciated

 

[ILENGINE]

the valves are not readily adjustable. Without removing them from the engine, and grinding the stems shorter to obtain clearance. Valve seats coming out of the block are farily common, and could cause a backfire, clicking noise.