Tue, 08/24/2010 - 14:30
My '68 R60/2 has Bing 1/24/150 on the right with #120 main jet, 1/24/145 on the left with #105 main jet with 1308 Jet Needle, #35 idle jet. This mismatch needs correction.
My research has led me to the information that BMW has switched to 1/24/125 & 126 for models after serial # 1814032 (mine is 1814309) and for these models main jet is given as #110. But Bing Carburator tech info for 600cc engines recommends main jet #125 for R60/2.
Considering that 1/24/xxx carb bodies are the same, can I cure this mismatch by simply changing main both main jets by #110, or will be better of if change to #125 which as recommended in Bing Carburator tech info for 600cc engines?
Any recommendations pls.
Best Regars
Ahmet ORHUN
- 646 reads
Wed, 08/25/2010 - 06:52
#2
1968 R60/2 Correct Main Jet Size
Thanks for your reply.
As I can gather from different sources and your reply R60/2 carburetors has changed over years from 1/24/125-126 (type 118) to 1/24/133-134 (type 120) to 1/24/147-148 (type 120) and finally to 1/24/151-152 (type 120). When I compare spec. sheets of all models, except 1/24/125-126, everything (Type, Slide, Needle Jet, Idle Jet, Jet Needle, Clip Pos. Idle Mix Setting) looks the same with only main jet changes from 110 to 125 in 1/24/151-152.
Do you have any recommendations on which main jet to use 110, 125 (or 120 as some are recommending)
Thanks and Best Regards
Ahmet Orhun
Wed, 08/25/2010 - 08:19
#3
If it were me, and you have
If it were me, and you have the Type 120 carb bodies, I would use the latest jet sizes per the Bing manual. Remember that the main jet is only a major contributing factor to running the bike once you get to well past 50% throttle, maybe even has high as 75% throttle. The carbs have basically three circuits - idle, midrange, and wide open. The idle circuit is controled by the idle jets and other small ports. The midrange circuit is controled by the jet needle and it's taper relative to the needle jet. Finally, once the jet needle has been pulled nearly completely out of the needle jet, then the engine is running on the gas that can get through the size of the main jet.
All of these circuits are in play throughout the RPM band, but lesser so depending on throttle. I would opt for the bigger of main jets if you are choosing. Since gas cooles the engines and you don't really want to run lean, that would be better. If after choosing a set of jets you find that the plugs look very dark and full of carbon, you may consider changing jets or changing the position of the jet needle to run somewhat leaner.
It's all a process to find out what works best for the bike.
Thu, 08/26/2010 - 13:31
#4
I'd take a look at the
I'd take a look at the current spark plugs and make a decision based on that. You may not need the same size jet in both carbs, but yours are about as far apart as I can imagine. It's possible someone drilled out the 105, it should be noticeable by comparing the hole sizes.
My R51's seems to always want the 105. I'm running 110's in my R60 because they gave me good throttle response. Can't imagine needing a 125 on a unmodified engine.
Short answer, base your size on your plug readings.
Thu, 08/26/2010 - 14:20
#5
1968 R60/2 Correct Main Jet Size
Gentleman,
Thank you all for your practical solution contributions. Following your advice I will by
buy several pairs of main jets (110, 120, 125), try starting fom 110 and check plug condition for optimumu result. This will keep me busy for some time but nothing beats experimenting 
Best Regards
Ahmet Orhun
Thu, 08/26/2010 - 14:21
#6
1968 R60/2 Correct Main Jet Size
Gentleman,
Thank you all for your practical solution contributions. Following your advice I will buy several pairs of main jets (110, 120, 125), try starting fom 110 and check plug condition for optimumu result. This will keep me busy for some time but nothing beats experimenting
Best Regards
Ahmet Orhun
Fri, 08/27/2010 - 01:21
#7
Good luck with dialing it
Good luck with dialing it in.Before you attempt to tune the jetting,I would make sure the compression is good/valves adjusted/points/timing is good/igniton system plugs wires/all past muster,then focus on carb jetting.
When setting up carbs, a good idea is to start rich (biggest jet)THEN lean it out until the plugs look good and does not bog from too much fuel on the top. It is a aircooled motor,so you want to stay on the more mocha/dark tan spectrum on the porcelain IMO.
Have fun,and I would HIGHLY recommend getting the EMPI carb synchroniser tools,which another member here had posted about and they are a godsend.
Basically they help you really dial in the idle as well as helping the synch the 2 cables so when the throttle opens,there is no "stumble"........the cables open the slides exactly on time and it makes a world of difference in the way the bike takes off,to the way it behaves in all the rpm ranges. I "thought" I had it spot on after messing with the carbs numerous times,and when I put the synch tools on,it showed me my vacuum was slightly off,so I evened out the vacuum readings at idle,and played with the mixture to even it out some more,and now it has had a consistent,perfect idle every time I ride it. What would normally take years of experience,doing it regularly can be achieved with the carb synch tools in just minutes.
Fri, 08/27/2010 - 05:21
#8
main jetting ????
I would start with the 120 main jets
and depending on the outside temps - your climate,
the main jetting requirement also changes from hot summer,
to crisp autumn riding days - if your riding a lot and
your really in tune with the different manners of your motor.......
115 would be best for dead-hot summer, 125 may be ideal
for chilly late season runs. The needle clip GROOVE position
is also important! and should not be changed after setting.
Go with the BMW manual spec on this. Just change the main
jet and leave the needle clip alone.
AND your ignition timing should be set FIRST and also never
touched again while making main jetting changes
Roland Slabon's book says that beginning with 1814032, R60/2 bikes got the 151/152 carbs. Those other carb numbers you have appear to all be for R50/2 bikes.
Essentially, I believe you could swap all the internals on your carbs for the sizes that are meant for the R60/2 and you would probably do OK. You might consider contacting Bing at http://www.bingcarburetor.com/bmw/bmw.html and posing your question to them. They might give you the "company line" that you really must have the right carbs for the bike. But in most cases, the internals passages of the carbs were the same. And since you're dealing with 24mm carbs, I would think they would be very compatible.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2