What are the chances he can modify it and improve it if he can't get it running well stock?
Sure , 4 valve heads and fuel injection and oversize pistons, new connecting rods and complete overhaul with new bearings will make it fast.
Did the op mention he wanted to empty his wallet and bank account?
He probably will balk at the price of a good head rework and cam and better valves.
The truth is a fast anything costs money.
Show me anywhere on this site someone with a genuinely high performance, rideable 350 that spent under $2000 to get there. Count labor, because the op is not likely a machinist.
You can make a fast 350, but you need a bit of resources.
The question of how do I make a 350 fast implies he does not have the knowledge, resources, or experience to do it, never mind cheaply.
I am not busting his bubble. He has no bubble. I doubt he even has soapy water.
A realistic answer to his question is what I said. Get it running well first. Then contemplate improvements. If you can't get it running well stock, you don't have the skill to hop it up.
I don't know the op, but if he knew how to increase performance his questions would be more about specifics, like cam grinds and duration.
My 69 cb350 stock would do the ton with a slight downhill run and a favorable wind. These bikes run well stock when well tuned. Carbs, timing, valve adjustment spot on.
Get there first.
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