I've recently purchased a 1990 Sirrus and I'm waiting to replace the threaded headset with a threadless one, so I can add a stem.
What's the size of headset do I need? 1 Inch or 1 1/8 Inch?

Cheers,

Definitely 1". Ritchey makes a decent one that won't break the bank, Cane Creek may as well.

Stupid question, but do you have a threadless fork?

I should have mentioned it's easier to get a new threaded 1" stem than a 1" threadless stem these days. 1" threadless was really only used a few years until 1 1/8th became standard. You can get a shim, but I don't like shimming things if I can avoid it.

Ok, I was confused as to what the difference between a threaded and treadless headset is. I have the old style stem at the moment and want to get a better fit with a longer stem. Below is a picture of what mine looks like.

What should I be looking for?

Thank you for the help. I'm a newbie when it comes to bikes, but I'm willing to learn.

You're looking for the same type, but with the neck portion longer/shorter, angled up/down as the case may be.

I seem to be limited on size options with the all-in-one quill. Would something like this product suit my needs? https://www.universalcycles.com/shopp...&category=1728
I want the ability to use modern bike stems as the selection is much larger.

That would do it as well..

You can do the conversion but you are not limited in size options when it comes to quill stems. There are plenty of quill stems out there. https://www.universalcycles.com/search.php?q=quill+stem and https://www.universalcycles.com/shopp...?category=1734

What are you trying to do?

I'm looking for a better fit. I feel the bar is currently too small.

Changing the stem won't help you with the handlebar. Just get a wider handlebar or a deeper handlebar or something that conforms to what you are trying to do.

I'm wanting greater distance from the bike. I'm roughly 5'10 and it feels a little off. Below is a picture of the setup.



What do you think?

That stem is probably too short. But you should start a different post in a forum on bike fitting. That way you'll have some idea of what length stem to buy. Also you need to buy the right diameter quill stem for that bar. But first figure out what length stem you need.

Thanks for the advice. I'll do just that.