Took the carb apart. Found two issues, I think.
1) The main nozzle/checkvalve seems like it's plugged. With the the fuel pump diaphragm and cover removed, there is a small hole visible, which connect to the High needle.
With the High needle removed, carb spray comes out the High hole. But the Zama technical guide says that, with the High needle out 2 turns, you should be able to manually blow through the hole, but should not be able to suck air through it. I put a tube up against it, but I can't blow or suck any air through that hole, with the High needle out 2+ turns.
I think the nozzle is clogged somehow. Unfortunately, it's brass, and pressed-in. The manual says to "carefully" drive it out, only if needed. Not sure how you drive it out from the inside of the carb, you can't reach it very well
I have some Chemtool B12 (the most "effective" stuff I have, along with spray cleaner), I could soak that portion of the carb in that, and see if it helps at all.
It is strange that *sometimes* it runs fine. And other times it simply will not rev up at all, and just dies when you add throttle, acting like something is plugged. I don't really understand why it would be intermittent.
2) The primer is still having trouble. I think one of the checkvalves in it has a problem. You have to pump and pump and pump before some gas might finally make it through the carb & primer bulb. Once some gets to the bulb, when you pump it, you see the gas just go towards the tank, and then pulls back *from* the tank, through the same clear line. It's just moving back & forth, not pumping in a single direction. There's a welch plug covering the checkvalve that I think is messed up, but the old carb kit I have handy does not have one of those plugs, so I don't want to remove it.
Is there a way to clean these? The nozzle is the more essential one to get sorted out. And a new carb is fairly expensive, at least vs things like rebuild kits, at $40+. Thanks.