The switch to unleaded gasoline might have had something to do with this.
I bought an old(1977) Simplicity Snowblower because it could throw snow farther than anything else ever made.
However, it had an old Briggs & Stratton engine with a downdraft carb.
It did not run well on unleaded, even super. So, I started buying 110 octane leaded racing fuel at Haffner’s here in NH.
It ran great on that, BUT every time I used it my clothes STANK so much from the exhaust from burning that fuel. Not to mention it probably was not good for me to breath!