In the SI carburettor, the main jet is located in the jet block under the mixer tube and main air correction jet. It is responsible for making a certain amount of petrol available for premixing. With all tuning measures, no matter how small, it is necessary for the main jets to be raised, as they mainly impact on the middle and upper rev range. Their effect is linked very closely with the other components of the middle SI jet block and for comprehensive tuning, it is necessary for all of the components involved to be adjusted accordingly.

In recent times DELLORTO have regrettably been unable to deliver some of the more important jet sizes for their carburettors. The quality of certain after-market reproduction jets is unacceptable for us at SIP. For these reasons we have teamed up with the people at KOSO to have our own jets produced, complete with the SIP logo!

While the sizes of the DELLORTO jets can vary up to +/- 0.05mm from the given value, the SIP jets are much more precisely produced with their sizes only varying by +/- 0.005mm.

Those who've tuned carburettors and found the actual jet size does not correspond to the number engraved on the side, know what we're talking about. If 105 is written on it, then there'd better be 105 in it! Anything else is a cheap trick.

The size of the jets increases on the basis of one, two and three stages. The jets get increasingly richer. Simply attach the corresponding size to part no 4026.

The SI 105-128 and 130-140 jetting kits each contain 5 and/or 10 jets and are an ideal basic programme for any tuner.

Unfortunately, DellOrto does not follow a consistent system when naming its jets. Actually, it can be assumed that the number by which the single nozzle is named indicates the diameter of the hole in 1 / 100mm. This means that e.g. a 107 jet has a bore of 1.07mm. On the DellOrto main jets for the SI carburetor that is only partially true. Up to a size of 120, the bore diameter corresponds to the jet designation. From 120, the actual diameter increases faster than the designation of the jets suggests. This increase is independent of fluctuations or manufacturing tolerances, which further complicates a clean gradation between the numbers. When manufacturing the SIP jets for the SI carburetor, we had to decide whether we would make it exactly like DellOrto or if we had all jets manufactured exactly according to the respective designation. We have decided for an exact production according to the given measure. This provides better transferable results and a slightly finer gradation. Unfortunately, this leads to the problem that a tool box equipped with a mixed jet set makes carburetor tuning very difficult. Of course, we recommend simply using the complete jet set from SIP because they are manufactured with the tightest tolerances available on the market. For the switch from DellOrto to SIP jets, we have created a table. With their help can be compared, which corresponds to SIP jet of the respective DellOrto jet: