If you are thinking of changing to Dell’Orto carbs, there are a few inspection items that you want to be aware of. These are:
Head Spigots and Connections to Carbs
1. Be aware that you must have the appropriate sized head spigots in order to mount the 38mm Dell’Ortos. Most R-bike heads either have 32mm or 40mm intake spigots threaded into the intake side of the cylinder head. In order to mount the 38mm Dell’Ortos you must replace these spigots with the appropriate sized 38mm spigots, which were used on the R90S bikes and are still available from BMW. Remove the existing spigots with a spanner wrench after soaking them with good penetrating oil and leaving them overnight.
2. Sometimes the airbox connections need to be modified in order to securely fasten the Dell’Orto carbs. For an inexpensive custom fit, go to your local Napa auto parts store or hydraulic hose supplier and purchase a 6″ section of reinforced rubber hose (2 or 2 1/4″ I think but measure yours to be sure). Cost is cheap and you can get several sections cut from 6″ of the rubber hose.
3. When you get the Dell’Ortos, remove the fuel connection on the outside of each carb and inspect/replace the fuel filter inside. Filters normally cost $1.20 each, which is cheap insurance. Also, don’t forget to check and clean the BOTTOM fuel filters on your straight BMW petcocks, if you have them. This can be done without removing the fuel tank by simply turning off both petcocks and unscrewing the lower connection. Inside you will find a fine mesh screen that captures most of the contaminants in the fuel tank feeding to the carbs.