If you order a UNI filter like the one shown in the attached link it comes with a plastic cage. I have them on a couple of my bikes and they work fine. They don’t show the cage in the photo, but it is noted in the description.

imgur.com/a/m12upXa

thank you!

Well the 73 at3 is running but has issues.
I did replace tires and brakes, cleaned carb and oil tank and changed oil in the forks and transmission.

1. it is not charging the battery, ohmed out the dynamo and got the following readings
white(A) to green(F) 4.8 ohms
white to light green(M?) .4 ohms
not sure what they are supposed to be.
2. key in position 1 it runs well revs up to 7000 but in position 2 it starts cutting out at 6000 and turns off at 6500 and will fire back up when rpm's drop below 5000.

brushes have lots of life left in them and they ohm out as not shorted.

any ideas what I need to check next or what may be going on?

Connections in the ignition switch need checked. High revs = more vibration and it could be that the contacts in the problem switch position may lose connection at higher levels of vibration. Hope it's something simple like that.

thank you I will check it out.

There should be a Service Manual in the Tech Library (see top toolbar), and in there it should walk you through the tests and readings needed to address your issue.

The CS5 and RD200 use a similar starting/charging set up, and often on those the regulator needs cleaning out - again, details should be in the Service Manual.

The Service Manual might be a combined one.

GR8UNCLEAL, thank you so I looked further down in the service manual that I am using and did find what ohm readings that I was looking for. Then I found another wiring diagram in tech library and it actually put wire colors to the letter designations so that I now know which wires to test.

I've always had great results following the troubleshooting menu in the manuals rather than "winging it" with ohm readings.

The early AT (1969) manual has the better explanations if I remember correctly. Or it might be the later 74-76 DT125 manual. The 12v starter-generator wiring and operation was the same on the 125 Enduros from 69-76 so looking at the system in all the manuals can often be helpful.

Also, in the Tech Library there is a "Full Yamaha Shop Guide" also from 1969 that has a lot of general theory and can sometimes answer questions the other manuals don't.

MarkT you are correct the 69 manual does a better job of explaining it.
So what I have determined is that one of the field coils is not ohming out correctly and is showing only .4 ohms . The other field coil ohm's out at 4.8 which is where both should be.
It would be great if someone could verify the 4.8 ohms on the one I believe to be good. the field coils are the 2 greens connected to the dynamo. I disconnected the white wire and both greens then took my readings from white to each green.
My question now is does anyone rebuild these field coils or can they be swapped out from a used one that is on ebay? I hate to spend $80 plus on a part that one of the field coils may be shorted or open.

How do you know both should be the same ohm reading?  

The starter-generator isn't what it seems at first glance.  It has two separate sets of field windings.  One set for the starter and the other for the generator.  One set of field coils has heavy wire windings for the starter, the other set is finer wiring for the generator.   Could you be measuring the different windings?  It makes sense the starter windings would have a lot lower ohm reading.

Again, I've had success following the troubleshooting procedure in the manuals.  I don't recall any mention of "ohm readings".