So I'm getting ready to start working on my 2003 non CA bike again. It's been sitting awhile now. Anyway, I purchased a used complete throttle body assembly part# 16400-mcz-672 that I do not have in hand yet. I am now realizing that that part number lists only the 2005-2007 bikes and the correct part number for the earlier years was 16400-mcz-671. Is there any reason the assembly for the "newer" bikes won't work?

Interesting. I'm sure the wheels are turning, round here..

Yikes!
That's a complication I have no idea about.
Could you tell if both versions were complete with a pre mounted Throttle Positioner?
That question being a WAG.
What would be helpful is understanding what Honda deems as being a trigger to change a P/N.
Maybe there are circumstances where a part fits, has the same function, but some non fit non function detail is different and triggers a P/N change as the part is no longer 100% identical in every respect.
My gut feel is there is no issue here, but maybe there is, and it'd really nice to know one way or the other.
Thanks for putting it on the table!

I've been watching this thread all day, suspecting you would be the first to respond with any meaningful input, but I'm somewhat disappointed in your failure to list all the known differences... C'mon man...lmao

Happy Thanksgiving to all

Thanks for the input. I thought the only things that changed from 04-05 were paint choice and caliper color. I guess I will wait for it to come and compare them.

I suspect Honda assigns a new part number when an earlier identical part becomes unavailable.

Yes indeed, a very Happy Thanksgiving to all those in the USA.

Thanksgiving is the one thing we Canadians know we'll beat you to every year without failure, ours being mid October.

As for differences, please cut me at least some slack.
If it ends that a visually comparative examination is the only means available to us, I'd start with the following:
Vacuum taps positioning and function.
(IF the TBs as a P/N come with the vacuum hose network, look for changes to the execution, especially the manifolding details.)
Starter valve details and actuation.
Throttle drum re any changes through entire range of travel.
Hopefully this will reduce your level of disappointment at least enough, so as not to mess with your appetite for lots of turkey.
Otherwise, I'll be feeling awful about it all.

THERE. Meaningful input. Finally.

I'm chuckling....................
AND I feel validated.
LoLs!

Save those chuckles, if you will. I much prefer expounding from your corner, sir.. lmao

https://en.wikipedia.org/wiki/Honda_NSR500
Someone had to blaze the trails

What a machine!
What an era !!!!!!!

I loved the 500 two strokes.
Fun at 90%.
Mean at 90+ %.
Vicious at 99+ %.
Let alone the tires of the day.

Powersportsdiscount shows that

16401-MCZ-671 is common from 2002 thru 2007.

https://www.powersportsdiscount.com/...=16401-mcz-671

The 672 is used from 2005 thru 2007 and must include the 671.

IF the website is correct, then it would translate that:
'671 is valid for use for all years of the 919 model run.
'672 reflects some change that does not affect fit, spacial requirements, functioning, or connections.

Thanks for scrounging about for the info!

Thank you. It was pulled from a low mileage 2005 and the seller stated it was the 672....Regardless, I guess it's going on a 2003 and I'll see what happens.

That will be the ultimate litmus test!

Could the manufacturer have changed between the model numbers?

My guess is that is another possibility.
Hopefully there's someone around that knows.