Hi folks, I have a barrel that I think is off a CT. It's 66mm (could be a bored out 125) the inlet is NOT a boost port, it's too small to fit my DT175 reed cage and has N.S stamped on the bottom left of the barrel. Does anyone know what this is?

Either we need a better description or pictures.  125 cylinders do not have a thick enough sleeve to bore to 175.

What do you mean the intake is "too small" for your reed cage?  Does it have a square-ish opening for a reed cage with 4 bolt holes?   Or is intake completely different with a carb-sized round hole and two bolt hole flange?

All factory Yamaha reed valve cylinders had the square-ish opening for a reed valve and a boost port transfer port above the intake port. 

Earlier models without the reed valve (piston port) could not have a boost port above the intake and don't.

There is at least one (rare) aftermarket cylinder I've seen that was reed valve and no boost port.  

Hi Mark, So it is a 175. It has the square reed cage opening with 4 holes but the cage wont go all the way in. The nose touches the (booster less) intake port in the barrel. Trying to send a picture but it wont let me.

Plus the barrel has only 6 fins

Right after more research I think I have a piston port barrel, but no idea what its off.

CT1 was the piston port 175 but piston port ended in "72 with CT2.
Just to confuse they still used CT1 prefix right through to CT3--i think.
Mark can correct me if i'm off the planet lol. 66mm anyway for all 175's.
Be good to have a pic please--hastle as it can be as can't go direct & need to use "Imgur" or similar.
I see ya ex Aus so talking Ag175 they had a smaller reed block & 'strangled porting' but hole spacing was same as rd350 & lots of others but 'that' RD block wont fit in width wise as the housing is cast narrower so can't quite fit without a lot of machining. Sorry that aint helping as yours fits in but bottoms out?. Sounds like it needs spacing back with something like RD200 used as original on their reed assembly.
Link here to mine--just easier for me to show this way. May look gasket but it's a very thick fiber spacer.
www.trademe.co.nz/a/motors/motorbikes/pa...2117106?bof=Dzc6eHvV
Re-reading, No Boost port, so i dunno anymore. Back in the box for me haha.

I thought we may be onto something with the AG175 barrel.  But the AG still has 2 more fins than mine. And what does N.S stamped on the lower left mean? Still trying to find a way of sending a photo.
Heres my email. murphtv@'ll attach a couple of photos. Justin

Cant send my email number. So bit stuck now.

I just use Google photos & post a link as I've no mastered it right but gets the job done easily. Looks like Imgur is the main one others here use. I really really want to see pic now haha. Keep trying but someone here will help you through it I'm sure.

The later ag175 has 6 fins but it's held down by a different method with studs on top for the head. Boost port wouldn't be easily visible looking from the inlet but look back from the other side can see it. That model started in 1980, grasshopper 175. But the bad news is that won't fit on the early cases as has studs further out. I guess it's not one of those after all that. I can't add a photo easily on my phone as I can't multi task haha without loosing it all. Just google image AG175G should find one.

Just thinking. I have a TY175 cylinder on my early AT1 but can't remember the number of fins. Is held on the old way holding the head & all on with 4 deep nuts down through the fins.

img.vdoerig.com
  Murph hears a quick way to post a link for your pictures  on Imgur