I welcome both to offer some wisdom along side their laughter.

I received the nos needle jet but it unlike the other two jets it says "213 0-6". The older ones say "215 0-6".

Perhaps I ordered the wrong one. The parts lists 301-14141-36 and that the one for the AT is 314-14141-36. I was concerned since the 314 prefix is usually associated with the CTs. But other than the model inscription the only difference was in the number of holes in the jet's neck. two on either side instead of the 2 on one side and three on the other.

I installed it and took a spin. The throttle response was much crisper and the bike accelerated more quickly and easily.

I still have the wah-wah lurching/surging during zero throttle deceleration but I will wait until the new jet needle arrives to worry about it.

The 213 or 215 is the "series number".  Sometimes the stamping of the number is hard to read?  There could have been an update too.  Anyway, the actual size is the "O-6" part of the number.  The AT and CT used the same carb body and same needle jet in 72-73.  The needle was different. 

The closed throttle decel surge you described sounds pretty normal and the pilot jet/air screw would have most effect with throttle closed.  Might be a little lean on pilot. 

 

Thank you Mark. You have tremendously helpful. With this issue and the last half a dozen.

I have a resolution to the surging on deceleration. The secondary outlet from the pilot jet hole that comes out at a diagonal towards the reed valve was clogged. A couple of days soaking in chem-dip and a reaming with a single brass bristle pulled from a wire-wheel seems to have fixed it. It is not 100% but very close.

Very very good point & it's a hole that's overlooked more often than not.
Progression hole.
Very good point. & i believe pilot jet can be increased or decreased to alter how that works then air screw reset/altered for idle.

As you all know - I follow these threads. The diagonal hole that spits fuel from the pilot jet should not be overlooked. Air alone should be enough to clear it, except with ethanol gas. Having a loop 10 power magnifier is crucial at ages above 35. 

With this determination, that particular orifice does not have anything to do with letting off the throttle in my opinion. That orifice helps start the bike. After that it’s idle only. 

Deceleration is not as important as acceleration on a two stroke. You don’t tune by deceleration. Only acceleration..

Therefore and furthermore, it becomes moot after making certain that is 100% obstruction free.

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