Any idea why yamaha wouldn't have shown the spec in those manuals I mentioned?  For those particular years? Is the book you got the information from made by yamaha?

Yamaha specs are often missing and sometimes the same manuals has different specs for the same thing like float level. Seems like sloppy editing more than anything.

As far as not listing the specs it makes sense to me. It's not a replaceable jet and not showing anything stops people from bugging the dealer about a part that doesn't exist. It's not a calibration that is normally changed.

Specs came from Clymer manual who got a lot if not all of their information from Yamaha and the bikes themselves. I haven't found many errors in their specs.

I'd take manufacturer service manual over Clymer. I've personally seen Clymers manuals get specs wrong, pertaining to odd variances in years. Arctic cat 90's snowmobiles, they had numerous things listed wrong, specifically pertaining to jetting.

The 71 years are listed that way in 2 manuals each.

Doesn't make sense to me. Why decide for 1 or 2 years your not gonna tell the customer what spec something is, then go back to showing them? I honestly believe there is more to this, but the only way would be to actually inspect known rt1 carbs, or 1971 only dt1 carbs.

Sometimes I regret even trying to answer.  I had a feeling this question was one to stay away from. 



 

yep, i am that guy...
I wish I still had my rt1b carb, then I'd not be asking this question!

Here is an ebay listing, rt1mx carb.  A couple of pictures glance into the air jet passage

Ebay item number: 185809175751
ebay link to carb

I swear it's blocked off, like they never drilled it out from the factory..

sorry, I couldn't directly attach a link.  Anyone that is bearing with me, THANK YOU!

Ebay prevents "hot linking"...  the forum software tries to post a preview of the ebay item which ebay no longer allows, I added the link into your post.

The center port is the one in question.  The port on the right is definitely blanked.  As it should be.  The center port looks open to me.

The left port has a brass ball inserted.  That means the idle circuit is pulling air from the center port.  I think it effects the amount of air/fuel delivered from the pilot circuit at higher speeds.  (Pilot circuit never stops delivering some fuel) They connected the main (center) and pilot (port on the side with the air screw) on some carbs, not all.  If the center port was disabled, why would they go through the trouble and expense of the extra drilling and the brass plug? 

 

It must still be getting air to the pilot circuit, but beyond that it looks undrilled to me.  Yes the passage in the center.  Hard to say in a picture, and I doubt I'll spend 250 on it to find out, lol.  Angle seems to line up with the passage in first picture.  I can't see any orifice or brass.  If anyone has a genuine rt1 carb and would be willing to look, I would be very grateful!

Center air passage is air to Needle Jet.

cliff

Yes. That is where the air jet goes.