Tightening would give a longer throw. Whenever I check the belts, I make sure there is sufficient slack with the belt disengaged. When pulling the lever to engage, I want the belt to loose its slack about 70% of the way through the pull. The extra 30% of tightness of the belt gives a little added pressure of the pulley.

thanks for the advice. one more question, the manual suggests that the augur cable be readjusted after changing the belt. how important is that? It doesn't feel all that much different to me after the replacement.

It is one of those times to set the book down and adjust the belt somewhat tighter than the instructions call for. It isn't the first time manufactures put too cautious tension adjustments on these. If it makes you feel better, re-tension the new belt after it's first use. Baymee's advise will get the job done.

Help - my about 10 year old MTD quit, impeller and rotor won't go around but can be truened by hand. Do I need to separatethe parts of the blower and find where they are hooked togther?

thanks again for the advice. my question though wasn't about the belt, but there's also this issue about resetting the augur cable up by where you squeeze it down on the handle. As I said, it feels fine to me, but what do I know?

My guess is they recommend resetting the cable due to slight manufacturing (length) tolerances in replacement belts. Sometimes 1/4" can seem like a foot!
I'd also not be surprised if the belt lengthened slightly after use, depending on belt quality.
Chances are, that if it "feels right", it probably is.

For screechy, you might have a shear bolt that broke. Look for a 1/4" hole where a shear bolt might go thru.