Sounds like you have something completely wrong with the carb. Take it apart and make sure you put it back together correctly or just buy a replacement.
MCP brake kit I found in eBay brand new for real cheap. Has some blemishes but I could care less. Welded some brackets, hooked it up and bled the system. Works like a champ. Now I can stop fast!
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contact the mfg and ask them why they are cracking. Maybe they have a better idea on why and how to stop it. It looks like the engines are just not meant to handle what you're using them for.
I had the same problem with my axle where the bolts were going down making the bearings bind. I just bent the bracket and it's good as new. It won't look the best and might have a bump but it will be straight.
Take a big pair of vise grips and put it right where you want to bend it. Pull the vise grips enough to bend it slightly. Don't get too crazy or you will bend it too much. Move the vise grip to any other part of the bracket that needs to be bent back.
Looks like you can put the vise grip...
Show pictures of both ends of the brake cable. There has to be a way to tighten it, if not then you can add a cable end that is adjustable.
The clutch needs a key on the shaft and a bolt to go into the end of it to secure the clutch.