In a motorcycle qould 20 psi make a big mpf diffence?

It is a honda nighthawk 450 1982. I have been getting 44 mpg at 20 psi and is now at 40

Tires should be at 30 or 32 psi

20 PSI WHERE?

Double the air pressure double the millage. That's why I run 200 psi in my tires.

The truth is for best millage run the max of the range that your owner's manual
recommends. Or go to Dunlop motorcycle tires, look up tire by bike and use what Dunlop recommends.

The optimum pressure should be somewhere on the side of the tyre. Most tyres usually run at between 30 and 32 psi, but a motorcycle tyre could be different. If you look under the seat, you might find a sticker that gives you the tyre specs.

Do a web search and find an owners manual for a 1982 Honda Nighthawk 450. It will list the tire size you need and the ideal air pressure of front and rear tire, it may also list a higher rear tire pressure needed for an additional passenger

Your motorcycle tires on that bike should be around 32 to 36psi. Yes, the tire pressures will make a fair difference in mileage. Perhaps up to 5mpg everything else being equal. Correct tire pressures do a lot to extend tire life too. Check your pressures once every day you ride the bike.

Speed and weight are the biggest part of mileage. Slow down and shed unnecessary weight for better mileage.