Have bryant 90 plus furnace model #398aaz036080 20 years old breaks once a year
New problem vent motor turns on pilot lights burner doesn't light turns off in 5 minutes
Cleaned fresh air and exhaust vent known concerns

Check gas supply
Check gas valve voltage during cycle

I'm not real familiar with that unit but,it sounds like it has an intermitent pilot. Does it have a spark ignitor on the pilot? If so it may just be a dirty flame sensor, not allowing the pilot to be sensed there for not bringing the burners on.

Gas supply is OK pilot light found problem with furnace had failed fame sensor install new senosrfurnace works fine thanks for the help

Yep those flame sensors can be a problem. Sometimes you can clean them.

I'd save the old one as I'm sure it just needs cleaned, about 90% of the time cleaning does the trick.

Another thing, make sure you have a good strong pilot when it lights, a furnace this old may have some build up in the pilot orfice,pretty common problem.