35303
12-30-2007, 09:08 PM
I made this change on a 84 r100 with 40 mm carbs and it brings an improvement to low rpm throttle responsiveness. It is simple to do. Has anyone else done this with success or problems?
Link here from Jörg Hau :
http://homepage.sunrise.ch/mysunrise/joerg.hau/mot/r100tic.htm#carb
Quote:
"Throughout the years, BMW has apparently used two different types of springs in the Bing carburetors.
Carburetor springs: old (bottom), new (top) The BMW spare parts catalogue tells that until end 1984, a spring with 115 mm length and about 30 turns has been throughout their model range, from the R45 through R65 up to the R80 and R100. The part number was 13 11 1 335 324. From 1985 on, the spring changed to 20 turns and an overall length of 120 mm (part number 13 11 1 338 134). Again, the same springs are used in all models, both the 40-mm Bings (Type 94) of the R100GS and R100R, and the 32-mm (Type 64) of the "late" R65, R80, and R100.
An interesting experiment is to put the "new" springs into the "old" carburetors.
Following a link detailed report from Rainer Restat who tried this on his R80G/S, I took the carburetor springs from my trusty R80GS and put them in the R100TIC. The result was ... a smoother idle and a better response to the throttle. In particular in the range between 2000 and 3000/min there was a noticeable difference, which is exactly the zone that I frequently use when strolling through the countryside. At higher rpm, there is no difference.
The "new" spring is harder than the "old" one, so a probable explanation is that the new spring reduces the pressure fluctuations that occur at low rpms inside the carburetor. A possible reason for the better "response" at low throttle is that the harder spring yields a reduced efficient cross-section when you open the throttle. This yields a higher air intake speed, which in turn leads to better filling and thus more "punch".
In conclusion, changing the "old" springs against the new ones is a very simple "tuning" which brings better idle and smoother acceleration at the low end. In addition, the new springs are far from expensive (about 10 CHF or 6.50 € a pair), so I really recommend this exchange.
Many thanks to Rainer Restat for this hint and his detailed report!"
Link here from Jörg Hau :
http://homepage.sunrise.ch/mysunrise/joerg.hau/mot/r100tic.htm#carb
Quote:
"Throughout the years, BMW has apparently used two different types of springs in the Bing carburetors.
Carburetor springs: old (bottom), new (top) The BMW spare parts catalogue tells that until end 1984, a spring with 115 mm length and about 30 turns has been throughout their model range, from the R45 through R65 up to the R80 and R100. The part number was 13 11 1 335 324. From 1985 on, the spring changed to 20 turns and an overall length of 120 mm (part number 13 11 1 338 134). Again, the same springs are used in all models, both the 40-mm Bings (Type 94) of the R100GS and R100R, and the 32-mm (Type 64) of the "late" R65, R80, and R100.
An interesting experiment is to put the "new" springs into the "old" carburetors.
Following a link detailed report from Rainer Restat who tried this on his R80G/S, I took the carburetor springs from my trusty R80GS and put them in the R100TIC. The result was ... a smoother idle and a better response to the throttle. In particular in the range between 2000 and 3000/min there was a noticeable difference, which is exactly the zone that I frequently use when strolling through the countryside. At higher rpm, there is no difference.
The "new" spring is harder than the "old" one, so a probable explanation is that the new spring reduces the pressure fluctuations that occur at low rpms inside the carburetor. A possible reason for the better "response" at low throttle is that the harder spring yields a reduced efficient cross-section when you open the throttle. This yields a higher air intake speed, which in turn leads to better filling and thus more "punch".
In conclusion, changing the "old" springs against the new ones is a very simple "tuning" which brings better idle and smoother acceleration at the low end. In addition, the new springs are far from expensive (about 10 CHF or 6.50 € a pair), so I really recommend this exchange.
Many thanks to Rainer Restat for this hint and his detailed report!"