* First of all, if the bike was just in for a tune-up, then I'd take it back and ask them to look at it again. Once you mess with their settings, then all your "warranty" is gone.

* How did they set the ignition timing ? It should have been set with a strobe light at full advance (high RPM) using the flywheel mark for full advance ("F" on some). Some instruction manuals say do this statically (engine stopped), but that absolutely does NOT apply any longer with 50 years of mechanical wear AND the use of modern fuels.

* What fuel are you running ? You should have 93 or HIGHER octane fuel, either ethanol or non-ethanol. This fuel should meet the requirements of Top Tier gasoline. Read and understand about quality fuel... https://www.toptiergas.com/

* When was the last time you replaced the air filter ?

* When was the last time you replaced the spark plug wires (which MUST be metal core, NOT automotive "resistance" core), and the resistor plug caps ? Wires and caps "age out" and must be replaced. Those plugs look suspiciously like someone has installed plug wires from a car. Try a new set of Airhead approved wires from Motorrad Elektrik... http://motoelekt.com/ . 

* The NGK chart listings for older motorcycles are all messed up. I believe BP6ES is too "hot" of a plug for general running. When you get the problem sorted, you'll probably test better with BP7ES plugs. ("6" heat range might be advisable only if the top end was burning a lot of oil or was very low on compression.) 

Bottom Line: If you see that any of the above changes need to be made, then your tune-up specialist doesn't seem to have much experience with Airheads. You might be better off to learn about your own motorcycle and start doing your own maintenance. Arms and neck covered with tattoos does NOT automatically qualify someone for Airhead maintenance. 

In the case of my R75/5 dying when returning to idle, it was the valve clearance collapsing to near zero. This was due to erosion of the valve seats, particularly the exhaust valve seats. This seat erosion is the result of unleaded fuel being run in a motor designed when leaded fuel was standard.

Thanks Richard and James for your comments / suggestions and for responding!  The plug wires are old and suspect so I ordered a new set if wires and NGK caps.  The spark is good but still - don't like the looks of the SP wires.  

Checked the floats and they are in spec and I tested with a cups beneath to catch fuel and they're where they are supposed to be. The main jets are #135 which the book says is stock for the carbs - only other possibilities are the needle and enrichment circuit but the mechanic who worked on the bike is competent and did a lot of other things over the winter that the bike needed.

It's easy to get upset when things don't work out after coming from a shop but with these old machines, it's not unusual and most people I know want to make a profit and an old machine probably needs a lot more than most of us want to pay for but nonetheless, I'm not new to wrenching with Airheads and generally prefer to do most of the work myself but given the various things this bike needed, I just had the local person do the work who again is competent with Airheads.

He did suggest the EME electronic ignition as did my other friend, the local Air Marshall in MN so we're going to install that and see what happens between the plug wires and a more modern ignition.  I have the Red Center ignition on my R65LS (which is the bean can design and not the same for the bike) but I have to say an electronic ignition does make life easier just like fuel injection but no joy in FI on my airhead.

There is a solution - once we nail it, I'll post again.  

Thanks much

Ken

1. Not all electronic ignitions (EI) are created equal. Some brands continue to use the (OEM) mechanical Auto Advance Unit as an integral part of the device. This means that the ignition advance curve is still designed around fuel that you haven't been able to buy in 35 years. AND, your ignition timing will only be as stable as a worn out 50 year old auto advance will mechanically allow. 

I highly suggest you shop around before making this major purchase. Compare the EME unit to a Boyer.

2. Realize that any EI installation will create its own set of new issues. Think of installing EI as converting a Victrola (pure analog) to a MP4 Player (pure digital). What could possibly go wrong ? Whereas the old analog system worked over a wide range of voltages (14 down to 8V), which made up for (really "covered up") funky electrical harness connections, frayed wiring, mismatched ignition coils, low battery condition, poor charging output, corroded battery connections, etc, etc. The new digital system (due to the absolutely rigid  demands of solid state electronics) works only at 12.0000V .

For this reason, most people will wait until the bike is running perfectly where all issues have been solved before introducing a new, radical change to an already taxed system. 

Hope this helps.