The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: manxr65 on May 02, 2010, 02:45:20 AM
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can i fit springs to my carbs, they are 64/32/353 to help with the idle as it is still revving a little high when im slowing down , this may help a little .
also can i remove the carb cv slide , it moves freely but would this make any difference . ie make revs come down quicker
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can i remove the carb cv slide , it moves freely but would this make any difference
If the slide moves freely then that isn't the problem. Can you remove the slide and put it back - yes easy just take off the carb top cover. Make sure it goes back the right way around there is a tab on the diaphragm and another check is that the hole in the bottom of the slide goes towards the butterfly end of the carb. Can you leave it out - absolutely not the carb won't work.
Did you set the idle speed at 1000 - 1100 rpm on a hot engine ?
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My carbs have the springs. I think they are less to lower the slide than they are to control the rate at which the vacuum diaphragm raises the slide, but I don't know for sure.
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My carbs have the springs. I think they are less to lower the slide than they are to control the rate at which the vacuum diaphragm raises the slide, but I don't know for sure.
i read in the ABC Archives -at least that's where I think I read it, IIRC- that the springs were fitted as an aid to closing the slide; hence the reason many early model Beemer owners retrofitting their carbs.
I put new ones in the 81's Bings and it made a real difference. Hello, Motobins.
Monte
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My carbs have the springs.I think they are less to lower the slide than they are to control the rate at which the vacuum diaphragm raises the slide, but I don't know for sure
According to Snowbum:-
"Some carburetor models have a large round many-coil fine spring above the slide, the purpose of which is to ensure positive slide return."
Sounds logical.
I can't help feeling that adding a spring where it was not originally fitted would also have some other effects like richening the mixture a little (slide won't rise as high) and as Ed suggests a change in damping or speed of response although that's primarily controlled by the vacuum hole in the bottom of the slide which connects up to the top of the diaphragm. As a matter of interest (or not) Harley riders drill this hole bigger on their CV's to speed up response
I've read that some have used a different spring rate and changes were for the better but I don't know if that would apply to adding a spring where it was not fitted as stock.
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I think that the springs were a basically good idea - to help ensure that the gas would be cut off when letting loose of the throttle and there might be the slightest bit of friction in the slide returning (or for the vacuum to diminish). I would assume/expect that one would have to readjust the mixture screw on the carbs if fitting them with springs when they didn't already have them installed.
The vacuum pressure (suction?) that these airheads generate through these carbs is relatively low, compared to higher air velocity designs, so it makes some sense that a small leak or bit of stickiness here or there can make a big impact on how the carb performs as it must operate in a much smaller range than the carbs in some Japanese bikes do.