I am going to throw this in for what it is worth when trying to fix carb problems.
A good soaking in white gas or Coleman campstove fuel is a good solvent dip for carbs
Changing out the diaphrams and the fuel inlet needle that come in those kits do little to improve performance unless the gaskets are leaking air or the fuel inlet needle isn't seating. The only way to find this out is to have some kind of pressure tester.
If the carb especially those Zama carbs that have a Welsh plug in the metering chamber this is usually where the trouble is that causes running problems due to blockage under the plug. I think that circuit under the Welsh plug is the primary circuit for idle and low speed adjustment and acceleration. Anyway if this circuit is plugged you might as well buy a new carb because it is almost impossible to get it unplugged and get new Welsh plug to reseal properly. Sthil was and might still be having problems in this area of those Zama carbs due to ethanol eating up the sealant they were using. Last I heard they have solved the sealant problem.
When you tear down your carbs pull out the H and L screws and spray some carb cleaner with those little tubes they furnish into the empty needle holes. Open choke and throttle plate and see if carb juice is getting into the venturi of the carb. If those passages are clear you should easily be able to see the carb cleaner entering the venturi which is the big hole in the middle of the carb.
Reapeated squirts may be needed to open and clear the passage, a little air and I mean a little air from an aircompressor won't hurt either, never full force from the blow gun attachment.
Not done yet, if you can locate the low and high speed jets on the metering side of the carb do the same thing with carb cleaner and a light touch with the blow gun.
Just be careful with the carb spray you don't need for it to back spray and get an eyeful of the stuff. Been there and it burns like heck.
This is what I do when I have carb problems if this doesn't solve the problem and every thing else checks out then it is time for a new carb.