When I go to the bike for its first start up of the day, its not an easy start . Its a 78 R100RS. Battery brand new also. Is this just part of its personality? or maybe something else? runs fine after initial priming, and a little choke then no choke.takes about 7 to 10 attempts before kicking over. then no issue. thoughts? the bike did sit for a while and carbs were cleaned. once warm, idles fine runs great.
thanks again for your time and I plan on bringing it to la canada on the 15th
hey Scott,
thanks so much that helps! im in Los Angeles so the cold factor?? its garaged but has been cooler than normal this year. ill take a look at what you saying. like I said once running its all good. just that first start of the day is the rough one. after that..all good
There is a small passage, not necessarily a jet, in the bottom of the float bowl. It is in the bottom of the little column that matches up with a brass tube that protrudes from the bottom of the carb body. That tube draws fuel from the float chamber and passes the fuel to the enricher. If the passage is obstructed, the enricher can not deliver adequate fuel for cold starting. If the fuel passage is obstructed on only 1 carb, the motor will be hard to start and run on the opposite cylinder. If there is an obstruction on both float bowls, well,.....
The enricher is a disc with a series of holes that get progressively larger. It is a variable jet the meters fuel thru what is essentially an extra fuel circuit in the carburetor.
I restored the cold start function of an R80G/S at a camp-out by filling the little column with brown whiskey and used the wire from a bread tie stripped of it's paper to poke the bottom of the column until a couple of pieces of dirt came pouring thru the "jet" and the brown whiskey poured out of the column and in to the bottom of the float bowl.
former Airmarshal, IL.
There is a small passage, not necessarily a jet, in the bottom of the float bowl. It is in the bottom of the little column that matches up with a brass tube that protrudes from the bottom of the carb body. That tube draws fuel from the float chamber and passes the fuel to the enricher. If the passage is obstructed, the enricher can not deliver adequate fuel for cold starting. If the fuel passage is obstructed on only 1 carb, the motor will be hard to start and run on the opposite cylinder. If there is an obstruction on both float bowls, well,.....
James said exactly what I was going to contribute. Look for a very small hole joining the 2 chambers of the float bowl. Since BMWs of this era typically take FULL "choke" to start when cold (even in summer with my 1979), if that hole is clogged then you're not going anywhere.
Further, if that orifice is filled then there is other crud circulating about. Start using only name brand High Test fuels that have cleaners. That stuff really works. You might also read about Top Tier Fuels.... https://toptiergas.com/
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you Sir Wobbly!
im on it tomorrow! keep you posted. gonna meet up with the Los Angeles chapter this coming Sunday out in La Canada for coffee! excited to get around true vintage BMW lovers
I like that whiskey and bread wire approach ! very Macgyver! lol
Hey Wobbly, I am happy to report that my R75/5 always starts easily without choke when the ambient air temperature is above 80F, if I have been running it regularly. I always search out the best High Test, non-alcohol, gasoline available in my locale. Maybe there is a difference between early 70's bikes and later 70's bikes when BMW started fiddling with the need to meet emission standards. As we both know, the advent of low octane, un-leaded gasoline created challenges for those of us in the U.S., at that time. The later introduction of ethanol in gasoline did not help. It actually created more troubles. I spent several hundreds of dollars to have my 750's heads re-built to compensate for the absence of lead in our gasoline. Your campaign to educate new owners about the trouble with ethanol fuel is much needed and helpful for new owners to understand how to care for our antique motorcycles. Keep up the good work.
former Airmarshal, IL.
I am happy to report that my R75/5 always starts easily without choke when the ambient air temperature is above 80F, if I have been running it regularly. I always search out the best High Test, non-alcohol, gasoline available in my locale. Maybe there is a difference between early 70's bikes and later 70's bikes when BMW started fiddling with the need to meet emission standards.
Likewise, I appreciate all your knowledge and input.
Yes, there were changes in the jetting between European and USA models (due to US EPA) starting in the mid-to-late-1970's. I have an older Hanes Manual that charts out the various jetting differences on all the models that was very helpful to me when I started down this road.
What you really need to be careful of is that too easy cold starting may indicate another issue. As was said, the needle jets get wallowed out just due to riding. Most owners with bikes over 60,000 miles can benefit from replacing the needle AND needle jet. The difference is so small that it typically takes a set of pin gauges to measure the increase in hole diameter, but it's there. That extra clearance may allow just enough additional fuel in, to allow you to forego the "choke".
Or, the same effect can be falsely generated by a "dirty" air filter. 😛
I don't think most people realize how incredibly precise these instruments are. Because the pieces are larger, they assume coarse adjustments and a "close is good enough" attitude, but they should actually be working with the care and reverence shown to any fine Swiss watch.
All the best !
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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