Need help on project

[RDnuTZ]

Do you have a manual? I never start into a new project without 1 for easy reference on stuff like this.

[RDryan]

I know the numbers can be hard to read on jets and I would suggest if you haven't got one already, get a magnifying glass. I used to try to wing it without and I finally gave up last year, what a difference it makes to have one. Mine is just a cheap hand held with two optics lens and a led lamp that really helps

[1976RD400C]

https://www.nichecycle.com/categories/carburetor/mikuni-parts-by-category.html

175 is the series type of the nozzle. There should also be a size of P-2 stamped on it too. That is the stock size for a 400 carb. Main jets should have a number on them too, if not, get some that do. About a 120 for a completely stock bike.

[Tropic-al]

Thanks to all that pitched in to help. Just to clarify your concerns and advice.
I bought a nice manual that includes 76 to 79 RD400 models. Unfortunately the only spec list I looked for at the end of the manual, only had RD400 F specs. After your reply I tried harder and found an Appendices list that included all models. So, now I have the jet sizes I need, able to read it with a well used magnifying glass. LOL!!! Still, my big problem is I need 1 of the P-2 needle jets as the threads for the main jet are messed up. I'll check Niche and Yambits as they seem to be the only ones that might have one.
If a member here would have one for sale, I would definitely buy it.
Thanks for the usual concern and advice to a new member. 

[Andrew S]

Niche Cycle on eBay has the 175 series P2 needle jets.  And they're located in Florida.

https://www.ebay.com/itm/162266775249

Look over the jet needles closely as well, if they're high mileage, the anodizing wears away and fueling profile changes drastically.  Niche has stock 5L1 jet needles too.

https://www.ebay.com/itm/161063800187

[Tropic-al]

Thanks for the reply Andrew. Niche did not have it when I contacted them but Economy Cycles got me both things. They just arrived yesterday.

[NYSingh]

I bought a nice manual that includes 76 to 79 RD400 models. Unfortunately the only spec list I looked for at the end of the manual, only had RD400 F specs. 

Sharing a few resources from my Google Drive that might be useful:

• Yamaha RD400 Workshop Manual
• Yamaha RD400 Parts Catalog
• Mikuni Tuning Manual