R100S. Overhauled the carbs with identical initial adjustments. The right side works well. The left side has strong blue spark but does not fire. Where to start looking/adjusting?
1. You didn't say, but I suspect this is at start up, while the engine is still cold.
Bings and Airheads need their fuel/air mixtures enriched to start. An often overlooked issue is the clogged hole in the bottom of the float bowl. This hole allows fuel to enter the "choke" jetting. No fuel entry = very lean mixture. Check this hole...
2. If you renewed your needles (and you should due to 50 years of physical wear), then there is a chance that one got placed in the wrong clip/slot. Unlike Mikunis or Amals, the installer cannot directly see the needle slot... which is critical. Use a caliper to check that both needles are protruding the same from the slide. Like this...
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you!!
Addendum...
The hole in the bottom of the float bowl is not a "jet" per se so you can use any wire, straw, drill bit, etc to open it up without fear of damage. I wouldn't purposely enlarge this hole, but it is not a precision metering orifice.
Also note...
Within the Bing, there are several mirrored parts. That is to say parts that look identical but are actually Left Side Only or Right Side Only. One of the more infamous of these is the rotating choke disc, located under the small 4-screw cover. For this reason, we highly advise that only one carb be disassembled at a time. Placing the choke discs on the wrong side will definitely cause hard starting.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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