Morning guys, appreciate any advice on the following. The forum has been absolutely fantastic and is an amazing resource. I am 31 and living in the UK.

I recently got hold of a 1971 CT1C - matching numbers and have checked against the very handy VIN register here on the site. I ordered a rebuild kit before the bike arrived, and when I was getting stuck into it, I realised the float bowl gasket was different and the pilot jet was too big from the CT1 kit. I have researched and checked on CMSNL and it looks like a I have a carb from a CT2 - it has the horizontal choke style rather than the vertical.

The bike came with the following jetting -

Main - 140
Pilot - 25
Needle valve seat - 2.5
Nozzle/needle jet - N-8
Needle - 4D-3

It idled fine but no real road tests as i'm doing the mechanical work on her as she is leaking horsepower like a sieve!

My question is:

Do I have a CT2 carb?
How will I jet this, my CT1 is piston port and the CT2 is reed valve I believe?
 

 from Salisbury!

Looking from above, what are the series of numbers stamped on where the carb bolts to the cylinder? These will identify the carb.

Best not to use brassware from a rebuild kit - original parts are still available from Mikuni and Yamaha.

Spent most of the 90's at Bulford camp wearing Batman pyjamas and eating sandwiches!

The first number/letter is ineligible but perhaps was a 4, then a B.

Sorry I can't be clearer on it - most things on the bike have been so simple and enjoyable just to clear this puzzle!

Given your age, I'm relieved that you were a nipper, as opposed to those being the army's uniform and diet! 

My only, vaguely disconcerting, experience of Bulford Camp was of going there in the 80s to look at a DT400 that an officer was selling. We stopped at the entrance for the car to be searched, but I got a little bit of a shock when I glanced up and saw rifles trained on us!!   Maybe it was because we had an old Austin Allegro! 

EDIT - Apparently my mother in law worked there as a civvie.

I played footy and cricket against and at some of the camps, though, although their teams were always changing, as the soldiers postings were changed.  

Anyway, back to the matter in hand, would you be able to post a photo or two of the stamped characters? Modern, digital cameras often provide more clarity than the human eye - certainly the case when I take photos of Gr8auntiepat's RD200DX and get great detail of the spiders' webs that I'd barely noticed otherwise!

Here we go - attached

Any ideas appreciated.
 

No, got me stumped for the moment.

Initial thought is that it might not be a carb for a Yamaha. However, MarkT or one of the other US chaps should be along soon to offer more helpful advice!

Yes, that does not look like the original carb.  Should have a three digit model number and possibly a two digit jetting revision on the edge of the mounting flange where yours says "B".

That said, it does look like someone has gone through the trouble of jetting to (mostly) correct specs.  Your Slide should have a 2.0 underneath.

Just make sure your slide needle is stamped 4D3...  not 4D-3.  And all jets and needles need to have the Mikuni "square in a corner of a square" trademark symbol stamped in them.  This is critical because companies like Shyster...  umm... I mean Keyster...  often include jets and a slide needle that may be stamped with the same numbers as original but are not the same calibration.  I've seen a lot of poorly running Yamaha's fixed by installing the correct original jets. 

Mikuni square symbol that will be stamped on all jets...  yes, even the tiny pilot jet and slide needle.
 

Here is a Yamaha jetting quick reference chart:
 

P.S.  The "-2" or "-3"  after the jet needle (aka slide needle) numbers is not stamped in the part.  The dash number indicates which groove the clip goes in counting down from the top.

I just edited my post because your jets are not exactly correct... the pilot is smaller...   If your needle jet and needle are the correct Mikuni parts, those are the most critical and possibly difficult to find as the needle jet is a different design than the CT1 type...  early model is "two piece" where the CT2/3 is a one piece needle jet that threads into the carb.

If you want an original carb, I have a few but shipping to the UK might be cost prohibitive.  Tip:  The AT1 and CT1 piston port models used an identical carb and jetting.  No difference between the 125 and 175 so you can use an AT1 carb on your CT1.

Thanks Mark! 

I guess it bears to mention that the #1 most common carb problem for a really poor running engine is the little o-ring on the needle jet...  if that o-ring doesn't seal into the float bowl well the engine might idle okay but will be very rich everywhere else.