I have had my D6 9U up and running for a few weeks now and all has been good. I went to start up the Pony yesterday and and I couldn't get it going. It is an electric start Pony with the battery removed. I have been jumping it off of my pickup. I know its 12V to 6V but I have been doing it anyhow. Anyway, last night I had the Pony running but it slowed and then quit. The motor sounded like it was laboring before it quit. When I tried to jump it again it wouldn't roll over. I wrapped a rope around the pulley and it was like it was seized. I checked the oil and, although low, it did have some in it. I pulled the spark plugs and tried to roll it over and it was the same. Then I noticed that the large nut (2 1/4" socket) that holds the large pulley/ counter weight that I wrapped the pull rope around was loose. I loosened it a little more and the motor started rolling over again. There is also a pretty good oil leak that appears to be coming from behind it. Is the problem that this pulley/weight is loose, or do you think a seal back there is gone and causing things to tighten up? Thanks.

Yes there is a lip seal behind the pulley so if it,s leaking in that area that,s where it,s coming from.I can,t see a reason by loosening the nut on the pulley would free it up unless there is some internal reason with the front main bearing that controls the thrust. I,d drain and catch the oil and examine it for aluminum chips or grains of it and if so you have a rebuild job on your hands.See if you have any back and forth movement of the crank by pulling out and pushing in of the pulley.

A loose pony flywheel will often knock out the locating dowel for the thrust bearing which then allows the crankshaft to migrate to where it will rub on the housing or cause binding.

Thanks for the input guys. Old Magnet, that sounds a lot like what is happening. What is involved in fixing that?

After first checking the crankshaft thrust....0.025 max. and in proper location, (no binding) you will need to pull the front cover to access the bearing and locating dowel. Also a good time to replace seal and check crankshaft for sealing surface.
If you find that the locating dowel is not holding the bearing in the correct location or has popped out, come on back with your findings.

Will try and get into it this weekend. Thanks.

If that is the trouble then a tear down by removing the crank will need to be done. I have seen lots of them dowels get loose and it wallowes the dowel hole out usually in the bearing so the bearing will have to be replaced if that,s what happened.Also have seen the bearing get loose (worn) in the block from it moving around but usually it doesn,t hurt the block, at least the ones I worked on which was dozens & dozens of them.