Not sure why i thought we're talking DT400 "or are we"--so here's the first thing that came up googling but for RD350 which would have to be similar DT400.
If we're talking DT175, i'll keep looking.
RD350 below.
yambits.co.uk/rd350-clutch-basket-gear-o-ring-p-46514.html

yamaha-enduros.com/index.php/forum/gener...asket-cushion-repair

Think this is the 175 type. Not to be confused with the 5 or so between the plates.

www.cmsnl.com/products/o-ring-353_9321098202/

Hmmm.
The repair manual shows that o-ring for the 100 and the 125, but not for the 175.
Plus the manual shows only the 125 having the steel ball, but not for the 100 and the 175.  But I have the steel ball in my 175.
imgur.com/a/mq3TEW6
And to think this all started with a question about an o-ring on the idle speed screw. Ugh!

im out for the day. very confusing isnt it. whatever fits will do the job so ;ong as ts a tight stretch ober the gear and down into the V gap tight.

I found an appropriate o-ring that fits perfectly into that groove.
It makes quite a difference.
Many thanks for your input on this Morley.

Ok. I got the clutch sorted out and it appears to function properly on the lift. It does require the ball bearing even though the exploded diagrams say that it doesn’t need one. Not sure what to make of that. Im guessing that someone has been in here before and did a little mix and match of clutch parts.

I haven’t been able to test ride it yet because I HAVE NOW LOST SPARK!!!
I had to walk away for a while because I’m getting pissed off. So instead I’m watching the Lions tromp all over the Titans.

Yamaha did away with the ball and brought it back after pushrods without ball would get friction welded together.  I don't recall on the DT175, but I know there was a service bulletin on the ~76 YZ125 to replace the non-ball set with alternate pushrod(s) that went back to the ball... 

I do see the ball on the Partzilla DT175C list...  and some alternate "Item 0" pushrod parts that probably were the original "non ball" pushrod and the "assembly" to replace a "welded" two piece set with the revised 3 piece set that used the ball?

Well that probably explains why the Yamaha service manual doesn’t show a ball. It was added later as a service bulletin. Ugh!

Now I am stumped with my loss of spark issue. I’m thinking it’s my ignition switch. I had noticed a while back that it would not run on the first key position. It had to be switched to second furthest position. 

I had to recruit my wife for this test. I put my Dewalt drill motor on the flywheel nut to give it a good spin with plug out and grounded. While spinning with no spark I had her move the key from one position to the next and it would get spark for short periods of time, but mostly it would be no spark.
 
I’ll say it again…. This all started with a question about an o-ring on an idle speed screw. 
 

Schu,

If it weren't for bad luck you have no luck at all with that 76 DT175. One of my favorite year 175's but I have never owned one. Your's sure looks nice.

One thing i always did when i was buying bikes like that running or not. Take the gas tanks off, clean and rinse anything bad out of them, remove the petcocks and clean and install all new seals and gaskets, remove the carburetors, clean and rebuild with new oem jets and needle valve assemblies and replace the fuel line, check air filters and replace the sparkplug. Always pulled the flywheel cover off and flywheel and checked and cleaned points and checked the left crank seal and end play in the crank bearing. That was minimum on every bike i bought.

Yes it get's costly doing this but saves me alot of headaches down the road. If a bike was in running condition this would get it started everytime, then i would see how things go from there. Of coarse it would have to turn over and have some sort of compression.

Should be a nice 76 DT175 when you get it all sorted out.