4, 5, or 6 millimeter
Thread Size: Dellorto jets in mopeds come in three thread sizes 4, 5, and 6 millimeter. Each thread size has maybe a hundred different jet sizes. They all fit and look the same but have different size pin holes.
Left, genuine (with “diamond INC” logo)
Right generic (with different or no logo)
Jet Number: Jets have a number stamped on them indicating the hole size. The number can have different meanings for different jet makers.
For generic Dellorto jets the jet number is the mm size.
A generic Dellorto 60 is 0.600 mm.
For genuine Dellorto jets the jet number is less than the mm.
A genuine Dellorto 60 is 0.627 mm.
So a genuine 60 is in-between a generic 62 and 63.
This sounds wrong but is true!
Dellorto Jet Sizes Graph, drawn in 2002
How this was determined: Here is a graph of 17 genuine Dellorto 5mm jets actual sizes. The direct measurement was done with a set of machinists wire gauges, in increments of 0.001″. You can see how the measured sizes fall nicely on two lines. The line for over-56 has less slope than the line for under-56. You can also see what drill sizes correspond to what jet sizes. This study was done in 2002 before there were generic jets. It was surprising to learn that the stamped number did not mean the millimeter size.
Dellorto Jet Sizes Graph, improved in 2019
Genuine 6413 (6 mm) Jets (M6-0.75 thread)
genuine closest generic
## inch size mm ## price applications
51 0.0215″=0.550 55 $4.00 generic 55 (= Dellorto 51)
52 0.0219″=0.556 56 $6.00 A55 smaller for high altitude
54 0.0228″=0.580 58 $4.00 generic 58 (= Dellorto 54)
55 0.0231″=0.587 59 $8.00 Tomos A55 243160 original
56 0.0236″=0.600 60 $4.00 generic 60 (= Dellorto 56)
58 0.0242″=0.615 61 $5.00 generic 61 (= Dellorto 58)
59 0.0244″=0.620 62 none generic 62 (= Dellorto 59)
60 0.0247″=0.627 63 $5.00 generic 63 (= Dellorto 60)
Genuine 1486 (5 mm) Jets (M5-0.75 thread)
genuine closest generic
## inch size mm ## price applications
42 0.0178″=0.451 45 $5.00
43 0.0182″=0.462 46 none pre-78 Ciao & Bravo
00 0.0182″=0.462 46 $5.00 generic 46 = Dellorto 43
44 0.0186″=0.472 47 $5.00
45 0.0190″=0.483 48 none 78-on Ciao & Bravo
46 0.0194″=0.493 49 $5.00
47 0.0198″=0.503 50 $7.00
48 0.0202″=0.513 51 $5.00 most 20mph mopeds
49 0.0207″=0.525 52 $7.00 78-83 Vespa Grande
50 0.0210″=0.533 53 $5.00 76-80 Garelli (some)
51 0.0215″=0.546 55 $7.00 85-91 Tomos A3
52 0.0219″=0.556 56 $5.00 almost all 30mph mopeds
53 0.0223″=0.566 57 $7.00 92-06 Tomos A35
54 0.0227″=0.577 58 $5.00 86-90 Derbi (flat reed)
54 0.0227″=0.577 58 $3.00 generic jet, no INC logo
55 0.0231″=0.587 59 none
56 0.0235″=0.597 60 $5.00
57 0.0239″=0.607 61 $7.00
58 0.0242″=0.615 62 $5.00
60 0.0247″=0.627 63 $5.00
62 0.0255″=0.648 65 none
64 0.0262″=0.665 66 none
66 0.0268″=0.681 68 none
68 0.0274″=0.696 70 none
70 0.0280″=0.711 71 none
Genuine 11600 (4 mm) Jets (M4-0.70 thread)
genuine closest generic
## inch size mm ## price applications
25 0.0107″=0.272 27 $8.00 Tomos A55 pilot jet
29 0.0124″=0.314 31 $8.00
30 0.0128″=0.325 33 $8.00 good for A55 pilot jet
32 0.0140″=0.355 35 $8.00 same as #80 drill
35 0.0149″=0.378 38 N/A
40 0.0170″=0.431 43 $8.00
42 0.0178″=0.451 45 N/A
44 0.0187″=0.475 47 N/A
45 0.0190″=0.483 48 $8.00
48 0.0202″=0.513 51 $8.00 Sachs 504/1A and 505/1A
50 0.0210″=0.533 53 N/A
55 0.0230″=0.580 58 $8.00
60 0.0250″=0.635 63 $8.00
Clone Carbs: Some Dellorto SHA clone carburetors have a different jet thread, M5-0.8. But the Runtong (China) SHA clone has the same thread M6-0.75.