yes, its a 1976 rotax 340cc engine. and yes i am running a 18 jackshaft sprocket and a 54 final drive axle sprocket. that would give me a 3 to 1 gear ratio. but what gets me is when i took it out and it ran strong for like 6-7 laps then i shut down to wait for the friend to come , unloaded him and we started up took off and then thats when it started to slip and did not stop. is their something that ether got hot or cooled that changed things. today i took the drive and driven to a snowmobile shop, i wanted to get some new parts for the driven and just took the drive with. the tech said that the drive looked good, wheels looked good bushings looked good and weights the same. but the driven? well that was another story, the plastic runners were shot, and were the runners fit into, it looked like someone had at one time ran it without the runners but with the new runners it should be ok. and that peace that ride on the runner was not looking good. he said it should have a flat surface were it would ride on the runners but they were a bit rounded. and the bushings were ok. SO i don't know if any of that would cause slipping but. all i did was put new runners on it. so what he recommended was to put the spring in the 6th hole turn it 1/4 and see what that would do for me. he thought i should get a replacement driven clutch but right now i need to spend the money on other things, you know what i mean? so i just helped it a bit and see what happens saturday. i don't know what else to do. i guess if i still get slipping i will have to go with the gear reduction. thanks.