TOPIC:

Hello everyone. I got my 305 back together and it works as well as before - which is not very. The idle holds okay at 2000, but if i back off the screw to lower it, it immediately drops to ~1000, then dies a second later. If I blip the throttle, it shoots up, then after a moment drops to 1000 and then dies. 

I had thought that part of this was butterfly adjustment - one being so open that when the other opens the RPM rockets - but I set them to be perfectly equal (off the bike) and it made it a bit worse. Balancing them with my carbtune made it MUCH worse. 

I don't have a perfect intake setup behind the carbs, so that may be part of it. The boots on the head are new.

While riding it's fine, pulls hard (for a 305) and doesn't stall if I brake down to 1k in gear. So, I'm at a bit of a loss. Hoping this sounds familiar to someone.

I can’t help because I’m not familiar with your style carbs. I’m sure you’ve covered everything that I will mention. What do the plugs look like. Have you checked the timing advancer? Battery voltage? And to be a real captain obvious, I’d concentrate on the idle pilot circuit.

Carbs are out of sync.

Yep

i had a Honda CB250 a long time ago with the 2 carbs so far out of sync it would stall if the idle was brought down to where it should be.

so whats making yours out of synch?
you mentioned the intakes. For sure fix that.
perhaps a blocked jet, idle/ pilot or air jet in one carb?

In my experience the intake has to be almost perfect or there's trouble on my 305. And its never perfect.

I've been keeping my old intake boots in a zip-loc bag and spraying them now and then with Rubber Rejuvenator regularly while I slog through my rebuild.  They are usually the source of my carb troubles but they are pretty well softened up now. Of course they won't stay that way long if I get it running again.

I'll spring for some stuff to make my setup less janky, and in the meantime look into the carbs. Seller told me he cleaned them then forgot how to put them together, but I probably should have gone over them first. He seemed nice!