Hey Everyone
   I am fairly new here although I have been reading and learning from all the knowlege. I am a recovering tech of over 30 years and just started to rescue some vintage bikes. I am resealing the pump on my 175B. The previous owner/s must have been exploring/tinkering and so I find the return spring broken for the pulley. I sourced another pump I could use as is after resealing it or take the spring from it and use it on my original pump. The sourced pump has a pulley with 363. My pump has 364. What is the differece here? 
 
Thx   

The pulley might have a different ramp or something...  363 should be the correct one.

364 looks like it was used on DT360 and MX360 and who knows what else.  Best I can say is it's not likely that pump is from a 175 and is likely not compatible with your engine.

Use caution if you don't know what donor pump is from.  Might "look" the same but the internal worm gear ratios differed over the years/models.  If you install the wrong pump...  if gears mesh at all...  you'll eventually strip/break/jam the gears and be looking for more parts and maybe an engine rebuild if you don't catch it in time.

DEET HERE REFURBISHES OIL PUMPS

Yes, DEET would be a good person to contact.  The pulley data I can find is limited but clearly says the 363 came on the DT175A/B...  but Yamaha data is not always correct.

75 should have had a red dot of paint on it if I remember correctly.

The worm gear is important....  pumps all look the same externally and sometimes people swap them and the gears don't mesh correctly.

DEET is a real expert on the pumps.