"The mainjet O-rings are size 3.9x1.2mm"
Thank you for the O-ring info.
"My best advice: look at the model numbers on your carbs"
"Your '77 version probably have carbs that have a model number like x46 or PD46"
069A is the only marking I can find on the carbs.
That much info is a wonderful thing!
Those carbs are the 'normal' type, so you have a good chance of sorting it out (not without some tinkering, though). The PD-style carbs are a straight-up vertical learning curve for the uninitiated.
With aftermarket brass, the parts are usually too lean. They seem to be patterned after the more popular Mikuni carbs: just for the record (to help understand 'why') their jets use both different numbering and different tapers in the flow paths - even different screw threads!
With some of the [popular for some reason] Keyster branded kits, the jet numbers are not the same as the Keihin numbers: they average around 7% to 10% lean for the numbers on them.
For example, your carbs likely came with Keihin's #78 (Euro) or #90 (North America) mainjets, which would be #83 or #97 (respectively) in Keyster parts.
If you have K&L parts, they are calibrated similar to the Keyster parts.
So, after you've [patiently] reinstalled your original jets, run (if your weather allows?) the engine 10 miles or so and then pull the plugs and show us the color: they will be either very dark or very white, depending on the numbers of your jets. You're aiming for something on the light side of tan (or grey, depending on the kind of gasolines you have).
If they are very white, you need jets with bigger numbers, and vice-versa with the dark plugs. And, a 5% change is quite a bit: this is a small-bore, small-displacement engine, so a little makes a lot of difference.
