no exhaust/wet-dry vac?

Sears Craftsman wet-dry vac model 113.179151/Air draws thru vac at about 75%/does no blow out exhaust at all/if you separate motor from cannister then turn on the power the air flows normally thru the vac then out the exhaust/as soon as you reattach the motor to the cannister the exhaust stops blowing/cleaned vac/changed filter/checked float/no change. Please help, Thanks pb