BMW R100 GS ’88 by-pass vacuum operated petcock
 

Hello,

I have a BMW R100 GS ’88, and recently my mechanic installed a by-pass vacuum operated petcock (he called it PRI in my service manual) in my right CV Bing (the one that at some time was leaking).

I would kindly request to shed some light on the following matters:

1. My mechanic told me that ALWAYS I will have to allow ON the left petcock (i.e. the one in which he had installed the that by-pass vacuum operated petcock. As such, I will not be obliged onwards to remove the petcock to RESERVE Or OFF position.
2. Does this modification affect (worsen) my km/litre ratio?
3. Does this modification has an impact on the litres in my reserve or in the basic tank? Because I have noticed poor consumption..11,5km/litre.. and some decrease in the fuel mileage before reserve is switched
4. He also told me that when the bike start stumbling I will only have to switch only the RIGHT petcock to RESERVE position-since the left one is constantly switched to ON (even when is parked).

Please note that my petcock has three positions: ON/OFF/RESERVE


Thanks in advance for your time

This thread should be placed in the "Airheads" section ...

And I don't think consumption varies by the placement of petcock valve on / reserve or such !

By the way welcome to the HUBB ...

The fact that your mechanic has fitted this tap suggests he has not dealt with the problem of a leaking carburettor properly, this could be the cause of your increased petrol consumption. I am not familiar with this particular modification but it should not be needed if the carbs are properly serviced and set up, my R80GS usually does about 15km per litre.