I've had pretty good luck soaking them in carb/parts cleaner using an ultrasonic parts cleaner. I found a good used one through craigslist and use the heck out of it for neglected carb cleaning: everything from cars to motorcycle and small engine carbs.

Then spray all the passages with aerosol carb cleaner. I'll sometimes carefully use a welding tip cleaner to run through suspect passages. I know that's not recommended. The pipe cleaner approach mentioned is a safer one.

Ditto on the previously mentioned accelerator pump plunger.

Generally I've been able to get them running ok again. I've never cared for the step up rod design, but it's sure used in a lot of different carburetors.

That said, I did have one of that style that never would cooperate no matter what I tried. That one went down the road at a swap meet, with a tag saying it had been gone through but would not run right. Guy took it for $25 and was happy to get it. He said he could fix it.

Being simple minded I've always preferred the Holley jet number scheme for tuning. The combination of jet, step up rod and springs always drove me crazy.