Optimized Pinasco SI28 ER - 28 mm carburetor for powerful largeframe engines
The Pinasco SI28 ER has a passage of Ø=28 mm. This means that it has 36% more intake surface area than a conventional SI24, on which the design of the SI28 ER is based. The body is slightly larger, but with the exception of the air filter, the tuning parts can be taken from the original Dell'Orto/Spaco SI types. The float chamber is 5 mm higher, which is intended to counteract weight loss on powerful engines. The generally enlarged fuel holes in the carburetor serve the same purpose.
In typical SI fashion, the basic tuning is set via the air jet and mixing tube, and fine tuning is carried out via the secondary jet, main jet and air filter.
INSTALLATION INSTRUCTIONS
- Only suitable for PX Lusso carburetor sump
- Original air filter does not fit (diameter of air intake + idle screw in a different position)
- Mixture screw is not aligned with the hole in the sump (shorten and slot the screw)
- Note the length of the enclosed M7 stud bolts, these are too short depending on the thread depth in the engine housing (if possible, do not screw in fully and secure with Loctite)
- Outlet pipe of the float chamber overflow is not aligned with the carburetor sump (drill out/adjust, otherwise the carburetor may jam)
- Holes in the carburetor body for the M7 stud bolts have very tight tolerances, widen them slightly if necessary
The SI28 ER is not intended for vehicles with separate lubrication. On models with an oil pump, the mixture itself must be premixed in the fuel tank. The oil pump itself can be shut down by simply pulling the oil pump shaft out of the engine housing (under the carburetor sump). We recommend adapting the carburetor sump to the larger cross-section. Enclosed are extended M7 stud bolts with shank nuts. These replace the original stud bolts or the stud bolts with hexagon socket used from 1984 onwards.
CONDITION
- Air correction nozzle: 160
- Mixing tube: BE2
- Secondary nozzle: 55/160
- Throttle slide (asymmetrical and wider) with air pocket on the underside
CONCLUSION: Perfect for inconspicuous but powerful street tuning.
NOTE: Please note that the air nozzle should always be adjusted in conjunction with the air filter/air funnel. An air funnel, for example, requires a smaller air nozzle than a completely closed filter. The secondary nozzle has a wide operating range in the SI. Its flow rate must always be added to the main nozzle. This means that simply changing to a smaller secondary jet can also require a larger main jet in order to keep the mixture at the same level in the upper speed range.
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