The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: georgesgiralt on November 23, 2016, 09:56:49 AM
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Hello !
For my research on jeting the bings I've made a lot of research on the BMW shop to get the proper P/N.
I think this would be of some use to others, so here are my findings.
I had no need to adjust the idle jet nor the choke so they are not listed.
Diaphragms : 13 11 1 254 774
Springs : L=121mm two versions:
Up to 1982 soft (33 turn): 13 11 1 335 324
After 1982 hard (22 turn): 13 11 1 338 134
Floats (weight 12.5 g) : 13 11 1 254 766 (beware of quality issues !)
Needle jets :
2.64 - 13 11 1 335 744
2.66 - 13 11 1 261 702
2.68 - 13 11 1 260 971
2.70 - 13 11 1 257 810
2.73 - 13 11 1 254 729
Needle Before 1983 : 13 11 1 255 840
After 1983 : 13 11 1 337 692
Main jets
(P/N is made of a base# 13 11 1 and a 6 digit suffix)
98 - 337 618
102 -338 175
105 - 337 062
118 - 336 871
123 - 336 839
130 - 338 133
132 - 337 989
135 - 256 612
138 - 337 691
140 - 336 877
142 - 337 889
145 - 261 703
148 - 335 601
150 - 260 972
158 - 337 890
160 - 262 428
162 - 337891
170 - 335 300
Air filter cover :
After 1980 and before 1983 : 13 72 1 337 228 two equal noses
After 1983 : 13 72 1 337 675 one big, one small nose
Hope this helps !
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Floats (weight 7 g) : 13 11 1 254 766 (beware of quality issues !)
7 g seems very light. Is that a Bing figure or did you weigh them ?
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It is a mean weight on both new and old (dried for month) floats.
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I was just going through some old papers that I had in my R65 records and found a Bing part number for their molded black plastic floats, 35-310 .
Part is no longer available from Bing, may be some old stock available from parts suppliers .
I waited too long, when I made up my mind to get a set, all gone !!!!
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It is a mean weight on both new and old (dried for month) floats.
7 grams stills sounds too light. I weighed my last new floats very accurately on lab scales at 12.495 grams.
I weighed the old floats after drying them out for 12 months. They did reduce in weight some but only down to 14 grams. Snowbum did extensive tests on drying out old heavy floats and also found that they do not return to their original weight.
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Maybe it is a typo, then. I'll check my note book and weight a couple I have.
By the way, do you know the relation between the main jet marking and hole diameter or surface ?
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By the way, do you know the relation between the main jet marking and hole diameter or surface ?
I can tell you for certain that the Bing jet size is not the hole diam in mm. For example a 123 jet is not 1.23 mm but a little smaller at 1.075 mm. I've tried to derive a mathematical relationship between jet area and jet size increments. I didn't come up with anything precise except to observe that each nominal jet size increment increase the jet area by approximately 5%
I have plotted hole diameter vs nominal size for jets up to my own size which is a 123. If you tell me what size you want to go up to I could extend the graph.
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Well, it would be great to know the hole dia for the jets in my table above.
Is this calculation the same for the needle jets ? And is it good also for other makes ?
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Oddly enough needle jets are the exact size in mm so a 2.66 is 2.66 mm and a 2.68 is 2.68 mm
I've edited the post above and derived the hole size for a 140 jet at 1.21 mm. Here's the data if you want to try plotting the graph to derive other sizes. I should explain that the data is derived by a combination of someone else who measured 200 bing jets with pin gauges and a few jets I measured myself. I found that they plotted as a straight line which enables me to infer other sizes with reasonable accuracy.
45 0.435
46 0.4445
48 0.46228
50 0.47752
52 0.49276
54 0.508
56 0.52324
58 0.54102
60 0.56388
62 0.58166
64 0.59436
66 0.60706
68
70
72 0.65786
74
76
78
80
82 0.73406
105 0.93
123 1.075
140 1.21
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There is no common system for jet sizes between carb manufacturers. As far as I know most have a system based on flow because if for example you increase the hole diameter by 5 % the hole area and therefore the fuel flow goes up by more than 5 %
To add more complexity flow is not exactly proportional to the area of the hole because of fluid dynamics. Two different makes of jet with the exact same hole size will not necessarily flow the same amount of fuel if the hole length and conical lead in to the hole are different. I've seen this comparing genuine Bing jets and some other substitute jets.
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Hello Barry,
I've checked the float weight and it IS NOT 7gr but 12.5 gr ! It is even written on all the floats I've weighted ! So I wonder where this 7 comes from ...
Thank you very much for pointing this out ! (I've edited the first post to show the correct information)