Hi Fellas, i have been looking on here for a parts list for the CT3 but cant see one. specifically i want to know the part number for the throttle valve can anyone help with this please. thanks..

Do you mean the reed valve? Have you looked at partzilla, you can find part numbers for every part on your bike.

CMSNL as well as Partzilla, and this is in the Tech Library.

Vintage Yamaha Enduro Fans - 71-73 100cc-175cc combined factory service manual and parts catalogue

The carb will probably be a mikuni VM24 so look.on the bottom of your slide. It will have a number like 2.5.

Order a VM24 slide with the same number and ensure it has the guide slot on the same side when the cutaway is facing you.

The same bike manufactured the same year often has different jets and slides fitted for different markets.  Looking at a generic CT3 parts list can get you in a right old pickle.  Much better if you have the old part in hand and buy like for like.  You need the right parts list for your specific bike.

Don't ask me how I know this...

The part number for the 2.0 cutaway CT2/CT3 throttle slide is 314-14112-20-00

Hi Fellas ,thanks for all your replies. i thought the carb i was using was from the ct3 it looks identical but i couldn't get the slide to go in ,it felt tight i tried a couple of others that i had but no good . the bike came to me in a few boxes and i just assumed the carb was the correct one, (lesson to be learned here !) . when i checked the ID mark it wasn't the correct one . the number on this one is 415 600 it is a mikuni v 24 i'm pretty sure .how would i find out what this carb will fit ?is there a mikuni chart somewhere with the numbers on ? the correct ID number for the ct3 is 314 et i think. any advice would be helpful thanks.

The model lists I have show 415 as being for a 1973 DT175, Europe or Canada. I wasn't aware that there was a DT175 in 1973, and I don't have any parts lists to progress this any further.

Mikuni slides are not a bunch of different sizes...  the diameter is consistent among the carb body size...  though details like guide pin slot and idle screw notch location vary depending on if the carb has a right side or left side idle speed screw.  

The flange mount carbs like you have can get "warped".  If the carb is on the engine, try loosening the mounting nuts and the slide might free up.  If carb is off the engine, check the mounting flange with a straightedge to make sure it's flat.  

Slide is a tight fit so even slight corrosion in the slide bore can cause issues.