16H mixture (?) problem

Cleaning the carb  properly is not easy , there are fine passages you have not accessed. drive out the jet block after removing screw from side of carb.

It sounds like you are going beyond rich, try the opposite direction. 

...and do check the mag points and perhaps oil the wick
..
But symptoms do sound like pilot jet blocked

Hi Russ,        My every day car is 32 years old and has a carb as standard equipment. Just recently it's general low speed running has become erratic, so I've tried cleaning the jets, changing the fuel filter and ignition advance. These didn't make much improvement and I am thinking the E10 fuel may have a different formula to previously.

My now sold WD16H ran better with one step larger main jet than standard. But that was long before E10. Ethanol blended fuels always runs leaner than pure petrol. So larger jets often required. E10 has a best before date of less than two months. Lighter components evaporate and the ethanol draws water from air moisture.    
One thing you could try is empty the tank and refill with some alkylate fourstroke fuel like Aspen. Often available in farm shops for use in lawn movers.      After six years sleeping with Aspen in the tank my WD16H started second kick. Had forgotten to lower ignition first kick, kicked back. Now have the routine that last two fills in autumn is with Aspen. Too much work emptying tank and carbs on half a dozen bikes.

As Robert says, it's not possible to clean the pilot circuit on a 76 or 276 without removing the jet block. They are easily damaged and best done after dropping the mixing chamber into a bowl of boiling water (the mazac body will expand faster than the brass) then use a softwood dowel to gently press (unless you have access to a lathe, in which case make up a two-part drift). The tiny hole low down on the engine side will probably be blocked.

I think I managed to knock mine out with a 3/8 drive extension bar , but as said a bit tight coming out , replace the paper gasket found under . 

Sounds like a pilot jet issue, I'd pay particular attention to the jet and carb passage ways maybe get a new jet, they are not expensive like the carbs! 

There really is no option other than to tap out the jet  block from underneath. It's not that difficult . Just remove any adjustment or locating screws and tap it out . Expanding the body with a little hot water will give a bit more clearance as the body often goes out of round . Inspect minutely the tiny fuel ways .

My 99 has a similar issue with a monoblock .it will idle fine and starts well. but for years would on occasion spit and stop when pulling away or riding slowly. New slides,several alternative complete carbs . pilot and slide changes and even a fully recon carb by Mr bratby has not cured it. Am now looking into the Advance retard unit which may be advancing too early . I suppose it could be worn valve guides allowing air in or an intake air leak.As the motor has not been appart for 30 years . When I will get to the bottom of it who Knows!.