I think you will find its your speedo that is running hot.
I have seen this before with other speed passion causing the complete setup to become hot.
I was running my 7.5t motor on 25/87 so your gearing isn't to far off.
A friend swapped his speed passion speedo to another brand and has never had heat issues again leaving everything the same.
You have mentioned that the speedo is what you have changed recently.
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