My STX 340 only runs on one cylinder - Why?

Hello!

I have new pistons and a new ignition coil at my STX 340 from 1977. But still, the left spark plug is always wet but all spark plugs got sparks. There is only the right cylinder who runs.

So to summarize this:

• The spark plugs got sparks
• New ignition coil
• The STX has a CDI box
• New pistons + rings
• New spark plugs
• The spark plug on the left cylinder is wet
• The right cylinder is the only cylinder who works
• The spark plugs got the spark exactly the same time
• No matter how I switch the spark plugs caps - still the left cylinder won't run

So what do you think the problem is?

The picture of the ignition coil is attached below.

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My STX 340 only runs on one cylinder - Why?