the secondaries (no pun intended) are not closing fully after I romp on it and let up. RPM is sticking at about 2500 RPM due to the secondaries not closing fully. When I turn off the engine and re-crank it, it idles normally. The old secondary diaphragm was busted, and the secondaries have probably not been exercised in quite a while. Looks like I tear back down and extract the secondaries and clean up the action? How do I clean them up to remove this hysterisis? Or, do you suspect something else that I may have overlooked?

When the secondaries are hanging like this, it is only usually a couple of things.
First check out if the shafts and butterflies are binding, that is the death knell for those secondaries,
The other common thing you have already found, somthing in that diaghpram/spring build up is a problem.

The other things to check is something inmpeding it which is pretty common in that secondary area.

Good Luck,

Bill White
White Automotive

I took the carb off and removed the secondary butterflies and shaft and cleaned everything up thoroughly. I even took some 600 grit sandpaper and lightly removed materials the cleaner wouldn't get off the shaft and butterflies and body. After doing all this, here's what I have.

When cold and not running and when cold and running, it operates by hand and throttle smoothly and it doesn't stick at all.

When the engine gets up to operating temperature the secondaries stick slightly open right before where they should be totally shut. Stuck there, the engine runs at ~ 2500 RPM. With one finger I can push the secondary nylon lever and the butterflies snap closed and the engine idle returns to ~ 700 RPM.

So when hot and the components have expanded there is a bind right before the secondaries close. Should I go back in and look for score marks that indicate the bind and sand it down/out? This may take a few times, because I don't want to sand too much at a time. And, if the bind does not have score marks, it may be difficult to find. So, would this be a good time to invest in a new carb?

In the meantime, I put the old busted diaphragm back in so I can drive it without worrying about the throttle sticking. Better safe than sorry, right?