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Starting a 1963 BMW R69S in cold weather
My 1963 BMW R69S starts OK but takes forever to warm up, even in the relatively temperate winter here in Miami. What I find so odd is that this motorcycle, designed and built in the chilly land where Mr. Fahrenheit was born, has no choke or other discernible accessory to enrich the mixture in cold weather. How can I get it to run on those 40 degree mornings and still be in tune when the temperature goes back up to tropical? - Glenn Patron/Miami, Fla.
A: Regarding your 1963 BMW, the shop manual I have shows you have Bing carburetors that look an awful lot like the one on my 1974 Jawa. There’s no choke, just an enrichment tickler like on an early Amal carb on a British bike. There are several possibilities, none of them all that promising. You don’t say if you are just having an idling problem or if the bike runs rough at larger throttle openings. If it is just an idling problem you could fit a larger idle jet to get you through the winter, but you will probably have too rich an idle once the bike warms up. If it runs rough in general until warmed up you could also up-jet the main, but again, it will likely be too rich when warm. You might be able to adjust the idle mixture screws on the carbs to provide a slightly richer mixture for your winter. Loosen the jam nut locking the idle screw first. I’d start with one-half to one turn counter-clockwise on each carb and see if that improves things. You’ll want to write down whatever adjustment you make so you can come back to the proper summer mix. I’d suggest a faster idle speed, too, but be aware that you’ll upset the balance between the two cylinders if you start twisting the idle speed screws without some way to synch the carbs. MC