i posted some picture on a snowmobile forum got some answear. Indeed it is a 70's engine, some guy said it look like his 75 ski doo snowmobile. Now if only i can find a manual for it.
yea it is a rotax i find the carb serial number and look it up and its from either 71-72 ski doo Olympique 399. Its definitely not a 340,but thats even better!