Took the carb apart and there IS an O-ring on the LSN. Good news is it could not be any easier to replace. Don't even have to remove the carb to access.
The O-ring resides behind the throttle arm and is seen surrounding the LSN once it has been removed. My 65 is GEN 1 so has the metal arm, but suspect all versions are identical. You loosen the metric set screw and pop the arm off. If the O-ring is missing or hardened from age then you may have to fully screw out the LSN to get it out. It sits in a cup shaped indent in the end of the throttle barrel so the sides prevent you from easily getting under it from the outside
You simply remove that O-ring and replace it with new. Ensure there is no grit or other contamination and the sides of the LSN are smooth with no marks. Lube the O-ring and LSN before assembly to ensure smooth adjustment.
The throttle arm compresses that O-ring slightly so you will need to push on it to fully seat against the barrel while tightening the set screw. Unless you get it back exactly the same you may have to readjust your throttle servo travel or rod length to get it working the way it did before.
NOTE: If you decide to, loosen the throttle adjustment screw and remove the barrel to make it easier to see and access. BE CAREFUL to not lose the small spring that sits around the fuel inlet tube at the other end of the barrel. This prevents vibrations from wearing the groove on the barrel and helps ensure smoother throttle operation. Not all Saito carbs have this, but it seems the 65-91 shares the same carb kit. Cannot remember if my 82 does, as well.
On that point, carb identification shows the kit mentioned to fit the 65-91, (P/N 521914) does include that LSN O-ring and is very inexpensive at approx $3-4.
Bad news is I cannot find that O-ring in stock metric charts, (mind you, coffee is still working its way through my system as I type). Perhaps someone can help identify one with the following:
I.D 3mm. C/S 1.5mm
If some P/N can be supplied perhaps a local bearing or seal house can source it for you. Likely be a minimum order amount. May be easier, (and more useful) to get the carb gasket set.
Hope that helps.
Last edited by Cougar429; 07-31-2015 at 03:48 AM.