I have the carbs balanced. I am starting at 30 degree at 1000 feet. Spark plug looks a nice light brown at a few different rev ranges.Yes, it helped me, too. Still not the easiest to start when 40F or below, but a significant improvement. Also helps to be sure that the carbs are properly balanced.
I am somewhat puzzled by the cold start issues some report with Bonnevilles. I am on my second 2007 and not a problem with either. Choke, button, motor starts. Maybe I am just lucky?
It makes me think that it is not the nature of the model but some undiagnosed problem with the bikes that start with difficulty.
Even my old Triumph start fairly easily in the cold - as long as the points and plugs were good. I'd tickle the carbs till fuel poured out, a few key off kicks to get some fuel in the cylinders, a bit more tickle and away it'd go.
I think I'd be doing some close looking at a new Bonneville that won't start at 30 degrees.
I think that this is how I will spend my time. I like the look of the color of the spark plugs - telling me the mixture is right at the moment. The bike has never liked the cold (as cold as it gets in California!)It shouldn t matter how lean the bike is jetted as soon as you pull that enrichener (choke) lever the bike should start.
It doesn t work like a normal choke (reducing the amount of air available,thus richening the mixture) it actual opens a passage directly from your fuel bowl to a jet on the inlet side of the carb. so it squirts unmixed fuel directly into the manifold.
Remove your carbs and check that when you pull the "enrichener" both slides move with the lever and that the rubber boots on the carbs. dont move with the slides. These boots are only pushed into place and dislodge easily allowing air into the enrichening circuit.