Plastic cap on air mix screw ???? BS-38's

A friend brought what appear to be 78-79 BS-38 carbs over to try them on my XS as a test. He had spent some time cleaning them and adjusting the floats etc. The bike fired up pretty quick with a couple of backfires when going from high idle to half throttle. I went to adjust the air mix screw and found that it was covered with a white plastic cap. there was a slot that you could adjust perhaps a half a turn. I have never seen these caps before on 78-79 BS-38's . Have you ????

tim

Yeah that's how they came, easily, and near universally removed. They got serious about it when the BS34's came out, the EPA death march had started.

Gary---Thanks for the reply. I have had perhaps six sets of 78-79 carbs and the caps must have all been removed before they fell into my hands. So they can just be pulled or snapped off ??

tim

Yep if you are careful you can remove, adjust, replace. I got one I removed from a Honda Reflex wandering around on my bench right now.

Yes, you can just pry them off. I wouldn't replace them, they'll just hamper adjustments in the future. Since they have never been off, that means the mix screws have never been removed. They've never had their sealing o-rings inspected and replaced if need be. The '78-'79 BS38s are the only BS38 carb set used on the 650 that had an o-ring on the mix screw. Through some trial and error, we've figured out the original size used to be 1.3mm x 2.5mm .....