I've been away from here for awhile. I had a 175 monoshock and a 250 monoshock and didn't really bond with either of them, so I sold them.  I managed to "stay clean" for about five years, but recently got the bug again and ended up with a pretty nice '73 about 3 weeks ago.  She shows some age and has some rust in places, but the paint is amazing and I like her just the way she is.
Anyway, it starts great, second kick this morning (getting colder here in MN), idles nice and pulls good, up until around 4000 rpm.  Then, it starts sputtering.  I think if I roll the throttle very gently, she will keep accelerating, but I'd obviously like it to run normally.  To me, this would seem to be carburetion?  I've seen a few threads where symptons like this have turned out to be the points, but I'd appreciate your thoughts.

Thanks!

Main jet O ring?

Thanks for your reply/suggestion, I will give that a try.

As stated by AirborneSilva #2. Oring seals the needle jet into thbowl for the side mounted main jet. No7 in the link. First i'd be tempted to try giving it a good hard rev--like hold it hard open--to see if it's limited & stays rich or will clear & rev out. In saying that an Oring is always a good idea. Other thought if that fails is exhaust partly blocked.

www.partzilla.com/catalog/yamaha/motorcycle/1973/dt3/carburetor

Thanks RT!